The JI
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     
 

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Murray, S. E.
Right arrow Articles by Stenzel-Poore, M. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Murray, S. E.
Right arrow Articles by Stenzel-Poore, M. P.
The Journal of Immunology, 2001, 167: 691-698.
Copyright © 2001 by The American Association of Immunologists

A Genetic Model of Stress Displays Decreased Lymphocytes and Impaired Antibody Responses Without Altered Susceptibility to Streptococcus pneumoniae1

Susan E. Murray, Holly R. Lallman, Amanda D. Heard2, Marvin B. Rittenberg and Mary P. Stenzel-Poore3

Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, OR 97201


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Stress pathways affect immune function, the most notable of these pathways being activation of the hypothalamic-pituitary-adrenal (HPA) axis. Although HPA activation has generally been relegated to an immunosuppressive role, recent evidence suggests that stress and HPA activation can be immunoenhancing in certain situations. To investigate specific effects of stress on immune function, we used a genetic model of chronic stress wherein transgenic mice overexpress corticotropin-releasing hormone (CRH), a primary mediator of the stress response. In these mice, CRH is overproduced in the brain, leading to chronic activation of the HPA axis. We found that CRH-transgenic mice have decreased leukocyte numbers in lymphoid compartments, with preferential loss of B lymphocytes. They also exhibit decreased Ab production and impaired isotype switching in response to immunization with a thymus-dependent Ag, phosphocholine-keyhole limpet hemocyanin. Despite these deficits, immunization protected CRH-transgenic and wild-type mice equally well against lethal challenge with Streptococcus pneumoniae, an encapsulated Gram-positive bacterium known to require Ab-mediated opsonization for clearance. While IgG responses are severely depressed in these mice, IgM titers are only modestly decreased. This fairly robust IgM response may be sufficient to protect against S. pneumoniae. Additionally, while total leukocyte numbers are decreased in these mice, neutrophil numbers are increased. This increase in number of neutrophils may compensate for the depressed IgG response, allowing adequate host defense during chronic stress.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Stress has long been associated with altered immune function, yet the mechanisms by which this occurs have not been fully elucidated. Several molecules induced during the response to stress have been implicated in immunomodulation, including catecholamines, neuropeptides, and steroid hormones. Corticotropin-releasing hormone (CRH)4 is a central mediator of the stress response. This peptide hormone is produced throughout the CNS as well as in several peripheral sites including the pituitary, testes, ovaries, heart, adrenals, and immune tissues (1, 2, 3, 4). CRH released from the hypothalamus initiates the neuroendocrine response to stress by stimulating adrenocorticotropic hormone (ACTH) secretion from the pituitary. ACTH then drives the release of glucocorticoids from the adrenal cortex. Activation of this neuroendocrine stress pathway, known as the hypothalamic-pituitary-adrenal (HPA) axis, plays a prominent role in the response to psychological, physical, or immunological stress (5, 6).

The key hormones of the HPA axis have been shown to modulate immune function. Glucocorticoids have profound effects on immune system development and function (7). While generally considered immunosuppressive due to their ability to induce lymphocyte apoptosis and inhibit proinflammatory cytokine production (8), glucocorticoids have recently been shown to possess immunoenhancing properties as well (9, 10). It is also clear that CRH can enhance or diminish immune responses independent of glucocorticoids (11, 12, 13, 14, 15, 16, 17, 18). Direct effects of CRH in the periphery have been reported (14, 19), and the discovery of CRH and its receptors in immune organs and inflamed joints supports the possibility of paracrine actions for CRH (20, 21, 22) (M. P. Stenzel-Poore, unpublished observations). Thus, it is well recognized that stress mediators can alter specific immune parameters.

However, the effects of chronic stress on immune function are less clear. Our goal is to understand the pathogenesis of immune dysfunction that occurs during prolonged periods of stress. We have generated a genetic mouse model of CRH overexpression to study the effects of chronic HPA activation on the immune system. These mice (CRH-transgenic (tg)) overexpress CRH in the hypothalamus and other areas of the brain due to the presence of a CRH transgene (23). These animals have increased circulating levels of ACTH and corticosterone (CORT, endogenous murine glucocorticoid), although peripheral levels of CRH are not elevated (23). Importantly, basal levels of ACTH and CORT in CRH-tg mice are similar to levels in normal mice during acute stress (Fig. 1Go). CRH-tg mice are capable of HPA axis activation beyond their elevated basal state during a superimposed acute stress, an effect similar to that seen in other models of chronic stress (24, 25). The behavioral profile of CRH-tg mice is also consistent with exposure to chronic stress. CRH-tg mice exhibit increased anxiety, decreased exploration, learning impairment, and decreased reproductive behavior (26, 27). These behaviors exist in CRH-tg animals in the absence of exogenous stress and can be exacerbated further following exposure to stress (27).



View larger version (25K):
[in this window]
[in a new window]
  		FIGURE 1. CRH-tg mice have increased basal levels of CORT, which increase further in response to restraint stress. Mice were restrained for 10 min in 50-ml polypropylene conical tubes. Blood was collected from the retroorbital plexus at the following times: basal (unstressed), immediately after restraint, or 20 min following cessation of restraint. Results are the mean ± SEM of eight mice per genotype; each mouse was bled at one time point only. *, p < 0.05, CRH-tg vs WT; **, p < 0.05, CRH-tg 30 min vs CRH-tg basal; Newman-Keuls post hoc test.

 
Previous studies using these mice reported marked reductions in cell numbers in the spleen and thymus with a more modest reduction in the bone marrow (28, 29). Compared with other cell types, B lymphocytes were found to be preferentially depleted in the spleen and bone marrow, and CD4/CD8 double-positive (DP) T cell precursors were preferentially diminished in the thymus. Ab responses were also decreased in these mice. Adrenalectomy partially reversed these changes, making it unclear whether glucocorticoids are solely responsible.

These preliminary observations suggested that CRH-tg mice may be quite immunosuppressed. We hypothesized that this immunosuppression may be qualitative as well as quantitative and that adaptive immunity would be targeted. Therefore, we examined leukocyte populations in primary and secondary lymphoid organs. Because DP T cells were decreased in the thymus, and the bone marrow exhibited a profound loss of B cells, we suspected that certain B lymphocyte subsets may be targeted preferentially. Here, we show developmental alterations of B cell populations in the bone marrow, wherein pre-B cells are depleted preferentially. In investigating lymphocyte function by measuring Ab responses to primary and secondary immunizations, we found that CRH-tg mice display high preimmune IgM titers and mount robust IgM responses to immunization. However, these animals show poor secondary IgG Ab responses, indicating a predominant failure to undergo isotype switching. Finally, we tested whether such immune changes affect survival in the face of challenge with a bacterial pathogen. Despite the defects in B cell numbers and Ab response, immunization affords CRH-tg mice equal protection against challenge with Streptococcus pneumoniae compared with wild-type (WT) mice. This may be due, in part, to an enhancement of innate immunity, as we found augmented numbers of neutrophils in CRH-tg mice.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Mice

The creation of CRH-tg mice was previously described (23). CRH-tg mice were subsequently back-crossed nine generations onto the C57BL/6 background. Mice were bred and housed in the specific pathogen-free facility at the Oregon Health Sciences University Department of Comparative Medicine. All procedures were approved by the Institutional Animal Care and Use Committee of Oregon Health Sciences University. Experiments were performed with minimal psychological and physical stress to the animals. Mice were used at 2–4 mo of age.

HPA response to restraint

Mice were housed overnight in pairs in shrouded cages to minimize environmental stress. Between 8 and 10 a.m. the following morning, mice were restrained for 10 min in 50 ml conical tubes equipped with airholes. Blood was collected from the retroorbital plexus at the indicated times in tubes containing EDTA (7.5 mg/ml). Cells were pelleted from collected blood, and the remaining plasma was stored at -20°C until the assay date. CORT (ICN Pharmaceuticals, Costa Mesa, CA) or ACTH (Nichols Institute Diagnostics, San Juan Capistrano, CA) was measured by commercial RIA or immunoradiometric assay, respectively, according to the manufacturer’s instructions.

Immunizations

For immunizations to examine both Ab titers and protection against S. pneumoniae, mice were injected i.p. with 70–100 µg phosphocholine coupled to keyhole limpet hemocyanin (PC-KLH) in 200 µl CFA (primary immunization, day 0) or IFA (secondary immunization, day 14). Blood was collected for Ab measurement at days 0, 7, 19, and 26, and serum was frozen at -20°C until the assay date.

S. pneumoniae challenge

Naive or PC-KLH-immunized mice were infected with varying doses of S. pneumoniae, injected i.p. in 100 µl sterile saline. For PC-KLH-immunized mice, bacterial challenge occurred 7 days after the secondary immunization (day 21). Survival was analyzed statistically using {chi}2 on collapsed doses, comparing total number of surviving mice: WT naive vs CRH-tg naive, WT immunized vs CRH-tg immunized, and naive vs immunized within each genotype.

S. pneumoniae culture

S. pneumoniae (Wu-2, a generous gift from Dr. J. Kenny, National Institute on Aging, National Institutes of Health, Bethesda, MD) were periodically passaged through WT mice to maintain a virulent stock. Bacteria were grown overnight on tryptic soy agar/5% blood agar plates (PML Microbiologicals, Wilsonville, OR). The following day, 5 ml of Todd-Hewitt’s broth supplemented with 0.5% yeast extract and 0.2% sheep blood were inoculated with an individual colony. This culture was incubated 12 h and then used to inoculate 125 ml of Todd-Hewitt’s broth supplemented with 0.5% yeast extract. Bacteria were collected at log phase, washed once, and dilutions were made in sterile PBS. Precise enumeration was calculated retrospectively by plating bacterial dilutions on thymic shared Ag/5% blood agar plates.

Leukocyte isolation

Bone marrow, spleen, and thymus were dissociated into single-cell suspensions, washed twice in PBS, and leukocytes were counted via trypan blue exclusion to determine viable cell numbers. After RBC lysis, peripheral blood leukocytes were washed three times in PBS and counted as above. These cells were then immunostained for FACS analysis as described below.

FACS analysis

Cells were preincubated with anti-CD16/CD32 (Fc block; BD PharMingen, San Diego, CA) to decrease FcR-mediated background staining and subsequently incubated in PBS/3%FBS with the following panel of Abs or appropriate isotype controls: anti-CD3, anti-CD4, anti-CD8, anti-CD45R (B220), anti-CD43, anti-CD23, anti-IgM, anti-IgD, anti-CD11b (Mac-1), and anti-Ly6G (1A8). B cell developmental stages were distinguished as follows: pro (B220low, CD43+), pre (B220low, CD43low), immature (IgM+, IgD-), and mature (IgM+, IgD+) (30, 31, 32, 33). All Abs except 1A8 were purchased from BD PharMingen as direct conjugates to FITC, PE, CyChrome, or biotin. 1A8 (a generous gift from T. Malek) is a rat mAb (IgG2a) that recognizes Ly6G (34), a differentiation marker restricted to neutrophils. The Ab bound to cells was detected with FITC-anti-rat IgG2a (BD PharMingen). Cells were fixed in 1% paraformaldehyde and analyzed the following day by three-color flow cytometry on a FACScalibur (Becton Dickinson, Franklin Lakes, NJ).

Ab measurement

Serum obtained from retroorbital blood samples was stored at -20°C until the time of assay. Quantitative ELISA was performed to measure phosphocholine (PC)-specific or keyhole limpet hemocyanin (KLH)-specific Abs as previously described (35). Briefly, 96-well plates were coated overnight with PC-histone or KLH (1 µg/ml). Dilutions of individual or pooled sera were added and incubated for 1.5 h at room temperature, plates were washed, and samples were detected by incubation with isotype-specific alkaline phosphatase-conjugated secondary Abs (Zymed, San Francisco, CA). p-Nitrophenyl phosphate substrate (Sigma, St. Louis, MO) allowed color detection at OD410. Standard curves generated with T15 idiotype (PC-specific) mAbs generated in our laboratory were used to determine the concentration of PC-specific Abs in serum dilutions. For IgG determination, a mixture of IgG1, IgG2a, IgG2b, and IgG3 T15 Abs was used. For PC inhibition studies, all wells contained 0.2 M free PC or control diluent (0.1 M phosphate buffer).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
CRH-tg mice have decreased cellularity and altered leukocyte populations in primary and secondary lymphoid organs

We analyzed the cellularity and leukocyte populations in primary and secondary lymphoid organs of naive CRH-tg and WT mice and found striking reductions in cellularity in the blood, spleen, thymus, and bone marrow of CRH-tg mice (Fig. 2Go). Spleen and thymus cell numbers were decreased 25- and 50-fold, respectively, consistent with effects previously reported with chronic HPA activation (36). Cellularity in the bone marrow and blood was also decreased, albeit to a lesser extent.



View larger version (17K):
[in this window]
[in a new window]
  		FIGURE 2. CRH-tg mice have decreased cellularity in lymphoid tissues. Spleen, thymus, and bone marrow were dissociated into single-cell suspensions and leukocytes counted by trypan blue exclusion. Results are the mean ± SEM of eight mice per genotype. *, p < 0.05; Student’s t test.

 
To test whether specific lymphocyte populations were preferentially decreased, we analyzed blood, spleen, and bone marrow by three-color FACS analysis to detect relative proportions of B and T lymphocytes and B lymphocyte precursors. The percentage of total B cells was decreased by 2- to 3-fold in the spleen and blood of CRH-tg mice (Fig. 3Go, A and B, left panels). Staining for IgM and IgD expression showed that this difference was primarily due to a loss of mature (IgD+) B cells, as seen when plotted as a percentage of total B cells (Fig. 3Go, A and B, right panels). We examined B cell precursors in the bone marrow to determine whether this loss of peripheral B cells might result from altered hematopoeisis. Total B cells in the bone marrow were decreased more dramatically (~6-fold) than in the periphery (Fig. 4GoB, left panel). We further identified pro (B220low, CD43+), pre (B220low, CD43low), immature (IgM+, IgD-), and mature (IgM+, IgD+) B cells using stage-specific markers (Fig. 4GoB, right panel) and found a near complete loss of pre-B cells in CRH-tg mice (Fig. 4GoA). In fact, as a percentage of total B cells, only the pre-B cell population was diminished (Fig. 4GoB). Thus, chronic HPA activation appears to affect mature B cells in the spleen and blood and developing B cells in the bone marrow as indicated by the loss in pre-B cells.



View larger version (31K):
[in this window]
[in a new window]
  		FIGURE 3. CRH-tg mice have altered T and B cell populations in peripheral lymphoid tissues. Splenocytes and peripheral blood leukocytes (A and B, respectively) were processed as described in Fig. 2Go. Leukocytes (105–106 per tube) were then stained with mAbs that recognize CD3, B220, IgM, and IgD and analyzed by three-color FACS. Results are the mean ± SEM of eight mice per genotype. *, p < 0.05; Student’s t test.

 


View larger version (35K):
[in this window]
[in a new window]
  		FIGURE 4. CRH-tg mice display a selective loss of pre-B cells in the bone marrow. Single-cell suspensions of bone marrow cells were stained with a panel of Abs to distinguish B cell developmental stages: pro (B220low, CD43+), pre (B220low, CD43low), immature (IgM+, IgD-), and mature (IgM+, IgD+). CRH-tg mice have a selective loss of pre-B cells as seen by low B220 and low CD43 staining (A) and when analyzed as a percentage of total B cells (B). Results are the mean ± SEM of eight mice per genotype. *, p < 0.05; Student’s t test.

 
We also examined peripheral T cell populations because we were interested in T-dependent Ab responses. Unlike B lymphocytes, the percentage of circulating T cells was similar between WT and CRH-tg mice (Fig. 3GoB, left panel). Moreover, in the spleen CRH-tg mice had a greater proportion of T cells (Fig. 3GoA, left panel), although the absolute number of T cells was still decreased. The CD4:CD8 ratio was not altered in these mice (data not shown). Thus, alterations in T cells populations are unlikely to contribute to an Ab defect, although we have not ruled out the possibility of altered T cell function.

CRH-tg mice exhibit an altered Ab response to PC-KLH immunization

To investigate the reported defect in Ab production in CRH-tg mice, we examined primary and secondary Ab responses to a thymus-dependent Ag, PC-KLH. PC is an important antigenic component of cell-wall polysaccharides of numerous pathogens including Gram-positive bacteria (S. pneumoniae), Gram-negative bacteria (Haemophilus influenzae, Salmonella), protozoans (Leishmania, trypanosomes), and parasites (tapeworm, nematodes) (37). Abs against PC have been shown to be protective against pneumococcal and filarial infection (38, 39, 40, 41, 42, 43). Thus, we elected to immunize mice with PC coupled to a protein carrier, KLH, which allowed us to examine thymus-dependent Ag responses and test whether immunization results in improved protection against a relevant pathogen, S. pneumoniae.

We found that preimmune titers of anti-PC IgM Abs were actually slightly higher (~2-fold) in CRH-tg mice than in WT mice (Fig. 5GoA). In addition, CRH-tg mice had primary (day 7) and secondary (days 19 and 26) anti-PC IgM responses that were robust, albeit somewhat lower (~3-fold) than WT mice. Primary (day 7) anti-PC IgG titers were low in both genotypes, but following secondary Ag challenge (days 19 and 26) WT mice mounted a strong IgG response. This response was severely decreased (10-fold below WT levels) in CRH-tg mice, indicating impaired isotype switching (Fig. 5GoB). This impairment is not due simply to delayed kinetics as IgG titers after immunization did not rise above levels seen on day 26 (followed out to 4 mo post-secondary challenge; data not shown). We observed similar decreases in IgM and IgG anti-KLH Ab titers, demonstrating that this alteration is not unique to the PC hapten response (data not shown).



View larger version (24K):
[in this window]
[in a new window]
  		FIGURE 5. Following PC-KLH immunization, Ab responses in CRH-tg mice are decreased in titer and differ in specificity compared with WT mice. Mice were immunized with PC-KLH (70 µg in CFA) and boosted on day 14 (70 µg in IFA). Serum was collected at the indicated time points and analyzed for binding to PC-protein by quantitative ELISA. ELISA plates were coated with PC-histone, and Ab binding was detected with anti-IgM-alkaline phosphatase (AP) (A) or anti-IgG-AP (B and C). For PC inhibition, wells contained 0.2 M free PC or control buffer (C). *, p < 0.05; Student’s t test.

 
The Abs produced in response to PC-KLH also differed in fine specificity in the CRH-tg mice. WT mice exhibited normal characteristics of the Ab response to PC-KLH, namely that the response was initially dominated by Abs that bind both PC-protein (or nitrophenyl PC, NPPC) and free PC. The majority of these Abs are known to be T15 Id positive (VH1/V{kappa}22) and protective against S. pneumoniae (40, 41). Following secondary challenge new clones emerge that do not bear the T15 Id and fail to bind free PC, but retain specificity for NPPC (35). These latter Abs do not protect against S. pneumoniae because they do not bind the bacteria. Such NPPC-restricted Abs eventually represent ~50% of the anti-PC-protein response in C57BL/6 mice (44). This Ab profile is shown in Fig. 5GoC, in which 90% of WT Abs obtained early in the response are inhibitable by free PC. However, by day 19 only 50% of the Abs are inhibitable by free PC, indicating a shift in Ab specificity over time. In contrast, CRH-tg mice fail to show this shift in fine specificity; >90% of the Abs in both the primary and secondary response are inhibitable by free PC. To ensure that the Abs from both genotypes were specific for PC in the context of protein, we tested them for binding to NPPC, a hapten analog that mimics the linkage structure of PC to the protein carrier. Abs from both genotypes were ~100% inhibitable by NPPC, confirming the specificity for PC-protein (data not shown). Thus, the pattern of Ab fine specificity indicates that as the response to PC-protein matures CRH-tg mice retain Abs that are inhibitable by free PC and do not generate Abs that are restricted to PC-protein. This suggests that these animals may differ from WT mice in clonal selection and V gene usage.

CRH-tg and WT mice are equally susceptible to infection with S. pneumoniae

The decrease in B lymphocytes and poor Ab responses after immunization suggested that CRH-tg mice would be more susceptible to infection with S. pneumoniae, a Gram-positive pathogen that requires opsonization for efficient clearance (45). We challenged CRH-tg and WT mice with various doses of a virulent strain of S. pneumoniae, Wu-2, to determine whether CRH-tg mice had increased susceptibility. Unexpectedly, survival was not different between naive mice of both genotypes (p < 0.3, {chi}2, Table IGo). Furthermore, most animals died between 2 and 4 days after infection irrespective of genotype, indicating that the kinetics of death were similar between the two groups (data not shown). We then tested whether immunization with PC-KLH, which is known to induce protective Abs in WT mice (46, 47), would provide resistance against S. pneumoniae challenge in CRH-tg mice. Surprisingly, immunization protected CRH-tg and WT mice equally well (>100-fold compared with naive) (Fig. 6aGond Table IGo). Again, there were no differences in survival between immunized CRH-tg and WT mice.


View this table:
[in this window]
[in a new window]
  		Table I. Naive CRH-tg and WT mice have similar survival rates after infection with S. pneumoniae

 


View larger version (17K):
[in this window]
[in a new window]
  		FIGURE 6. CRH-tg mice survive S. pneumoniae infection equally well compared with WT mice. PC-KLH immunized mice (9–10 mice per dose per genotype) were challenged i.p. with doses of 1, 10, 100, or 1000 S. pneumoniae organisms per mouse. There was no significant genotype difference in percent of mice surviving or average day of death. Both genotypes were significantly protected (~100-fold) by immunization (p < 0.05; {chi}2).

 
Augmented neutrophils in CRH-tg mice

It was unexpected to find that immunization afforded CRH-tg and WT mice equal protection against S. pneumoniae given the diminished B cell numbers and Ab responses. Abs are critical in clearing S. pneumoniae because opsonization allows phagocytic cells, particularly neutrophils, to engulf bacteria by binding via Fc and complement receptors (45, 48, 49, 50, 51, 52). Thus, we speculated that the protection in CRH-tg mice might result from increases in neutrophils that could compensate for decreased Ab titers. We examined myeloid and granulocyte populations using the specific markers CD11b and Ly6G. Both monocyte/macrophages and neutrophils express CD11b, whereas Ly6G is neutrophil specific (34). Monocyte/macrophage populations were similar in CRH-tg and WT bone marrow and blood, and these cells were increased in CRH-tg spleen (Fig. 7GoA). This is likely due to the B cell depletion, wherein a decrease in one population results in a proportional increase in others. The percentage of neutrophils was increased in CRH-tg mice in all lymphoid tissues examined (Fig. 7Go, B and C). Moreover, the increase in circulating neutrophils was so great (>10-fold) that despite the overall decreased cellularity, CRH-tg mice had greater numbers of circulating neutrophils per volume of blood compared with WT mice (Fig. 7GoD). Thus, despite decreased lymphocytes, neutrophil populations were increased in CRH-tg mice.



View larger version (36K):
[in this window]
[in a new window]
  		FIGURE 7. CRH-tg mice have increased numbers of granulocytes. Single-cell suspensions of spleen, blood, and bone marrow were stained with mAbs to CD11b and Ly6G to distinguish monocyte/macrophages vs neutrophils (C, lower panels). Neutrophils were also distinguished by high side scatter (SSC; C, upper panels). CRH-tg mice had an increased proportion of monocyte/macrophages in the spleen (A) and increased proportion of neutrophils in all tissues examined (B and C). The absolute number of blood neutrophils was obtained by multiplying the percentage of neutrophils by the number of leukocytes per milliliter of blood (D). Results are the mean ± SEM of eight mice per genotype (*, p < 0.05; Student’s t test). FSC, Forward scatter.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Until recently, the immunological consequences of stress have been viewed as largely detrimental. It is becoming increasingly evident that this view does not convey the complete picture and is inaccurate in certain situations. Decreased lymphocyte numbers occur following acute and extended periods of stress, but such diminution does not always lead to suppressed functional outcomes of immune defense. Furthermore, new evidence supports the idea that exposure to acute stress can lead to enhanced immune responses (9, 10). Some have proposed that while acute stress can be immunoenhancing, chronic stress is detrimental (53). Our findings with susceptibility to S. pneumoniae suggest that this may not always be true. Thus, while stress-induced modulation of the immune response alters certain components of the immune system (e.g., cell numbers, population composition), the consequences on immune function need to be analyzed individually. Furthermore, effects of stress on innate and adaptive aspects of the immune system are not necessarily synchronous; thus, suppression of adaptive responses may be counterbalanced by enhancement of certain innate components.

Using a genetic model of chronic HPA activation, we found strong evidence for changes in both adaptive and innate components of the immune system. Stress-induced decreases in lymphoid numbers have been a fairly consistent finding among most models of stress and HPA activation. We found that CRH-tg mice exhibit decreased lymphoid numbers in all immune compartments examined. This may be due to increased glucocorticoids that have been shown to decrease the size of the spleen and thymus, although decreased cellularity has not been observed consistently in the blood and bone marrow (54, 55, 56, 57, 58). Furthermore, lymphocytes are known to be particularly sensitive to glucocorticoid-mediated apoptosis; thus, we speculate that the decrease in T and B lymphocytes in CRH-tg mice is due to increased basal levels of CORT (58, 59, 60, 61). It is noteworthy that CRH-tg mice show a profound reduction in pre-B cells in the bone marrow, which to our knowledge is the first evidence that chronic HPA activation preferentially depletes pre-B cells. Again, this is likely due to excess glucocorticoids as del Rey and colleagues (62) showed that dexamethasone treatment induced widespread loss of pre-B cells, but had a lesser effect on pro- and mature B cells. Interestingly, DP T cells, which are at a developmental stage analogous to pre-B cells, are well known for their susceptibility to glucocorticoid-mediated apoptosis (59).

Precursor lymphocytes may be affected preferentially by glucocorticoids because these hormones play a role in lymphocyte selection. In the case of DP T cells, glucocorticoids antagonize TCR-mediated apoptosis, which allows selection of clones with low to moderate avidity for self Ags. Without glucocorticoid signaling at this stage, the threshold for positive selection is raised and T cells with low to moderate avidity for self Ags die (63, 64), although the total number of DP T cells generated in the thymus remains unchanged (65). In the case of pre-B cells, it is not known whether glucocorticoids influence B cell selection. However, our results showing that pre-B cells are particularly sensitive to chronic HPA activation raise this intriguing possibility. Furthermore, there is a marked difference in the Ag specificity of B cells induced by PC-KLH when comparing CRH-tg and WT mice. This difference in fine specificity quite likely indicates a difference in responding B cell clones and thereby suggests that the B cell repertoire may be altered during chronic HPA activation. Additionally, this observation is consistent with a failure to develop a strong memory response because NPPC-restricted Abs normally arise during secondary and memory responses to PC-KLH.

Depletion of mature B cells in the spleen was also evident among CRH-tg mice. This was unanticipated given that mature B and T cells are relatively resistant to glucocorticoid-mediated apoptosis (56, 57, 66). This could be a reflection of the decrease in B cell precursors, leading to fewer cells capable of entering the mature B cell pool. However, if this were the case, we would expect the proportion of immature B cells in the periphery to be similarly depleted. It is conceivable that hormones that act upstream of glucocorticoids such as CRH and ACTH may affect mature B cells in a manner that is independent of glucocorticoids (11, 13, 67, 68). In addition to direct effects on mature B cells, it is possible that chronic HPA activation leads to changes in specific factors necessary for B cell survival, thus indirectly limiting their development and/or expansion.

Adaptive responses are also impaired as measured by the ability of these mice to generate Ab responses to the Ag, PC-KLH. CRH-tg mice mount an IgM response to PC-KLH immunization but exhibit poor isotype switching. The precise mechanism underlying this impairment is not clear at this time. It is reasonable to speculate that B cells in these animals are unable to respond to appropriate signals needed to induce isotype switching or memory cell formation, perhaps due to altered expression of cytokine receptors or inhibition of signaling pathways (69). Lack of adequate T cell help, a critical component for isotype switching, may also be a factor. This could result from a decrease in T cell number, making cell-to-cell interactions infrequent. We think this is unlikely, because the T:B cell ratio is actually higher in the spleens of CRH-tg mice (data not shown). Instead, the T cells making up this population may be actively regulating B cell function. Alternatively, CRH-tg T cells may not express adequate levels of costimulatory molecules, such as CD40 ligand, or produce cytokines appropriate for class switching (70).

Surprisingly, immunization with PC-KLH provided CRH-tg and WT mice equal protection against S. pneumoniae. Given the low B cell numbers and poor Ab response, we predicted that immunization would be less beneficial to CRH-tg mice. However, because this was not the case, we need to consider that even the low level of Abs achieved in CRH-tg mice is sufficient to opsonize and clear S. pneumoniae. Immunization of WT mice with PC-KLH may elicit Ab titers that exceed those needed to protect against S. pneumoniae. However, previous studies have shown that when mice are immunized with pneumococcal polysaccharide, individual Ab titers correlated with survival in mice challenged with S. pneumoniae, indicating in that system Ab levels are not in great excess (71). It is also possible that IgM Abs play a more important role in bacterial clearance than has been appreciated previously. If this were the case, CRH-tg mice would be reasonably well protected given that their levels of anti-PC IgM were only modestly reduced. Indeed, an early study showed that S. pneumoniae preopsonized with IgM Abs obtained from pneumococcus-immunized animals were cleared more rapidly from the bloodstream than those preopsonized with IgG (45). More recently, a number of studies have shown a critical role for IgM Abs in other models of bacterial infection (72, 73, 74). These observations, taken together with the recent isolation and identification of a novel FcR for IgM that enhances opsonic uptake (75), support a vital role for IgM in defense against bacterial disease, particularly in the early phases of infection that involve phagocytosis and clearance of bacteria.

It is also reasonable to speculate that augmented innate defenses may compensate for the lower Ab titers, allowing clearance of bacteria that are not opsonized optimally. We found that CRH-tg mice have increased numbers of circulating neutrophils, which may afford significant protection in the face of diminished Ab responses. The increase in neutrophils seen in these animals is likely due to elevated CORT levels because glucocorticoids have been shown to increase the production, release from the bone marrow, and half-life of neutrophils (76, 77, 78, 79). Future studies are necessary to determine whether specific functions of innate immunity are enhanced in CRH-tg animals.

The idea that innate immune mechanisms may be augmented in CRH-tg mice is supported by other stress-related studies. Both stress and glucocorticoids have been shown to increase the phagocytic activity of neutrophils and macrophages (80, 81, 82, 83, 84, 85, 86, 87, 88). In addition, glucocorticoids induce molecules vital to opsonization such as complement and C-reactive protein, an acute-phase protein that binds PC and is protective against S. pneumoniae (89, 90, 91, 92, 93, 94). Other products of the stress response, such as CRH, may also modulate innate immunity. Recent studies have shown that CRH receptors are expressed on splenic macrophages and can be induced on neutrophils following immunization or restraint stress (21, 95, 96). In the case of macrophage function, CRH has been shown to increase superoxide production (97), suggesting that an innate mechanism of cytotoxicity could be enhanced by increased CRH production during stress.

Collectively our studies suggest that during stress, innate immune mechanisms are preserved while adaptive responses are clearly compromised. A balance appears to be achieved by these changes because CRH-tg mice develop an adequate immune response to protect against challenge with a lethal pathogen despite profound loss of B lymphocytes and diminished Ab responses. During periods of stress there are likely to be important demands on the immune system due to infection, thus stress regulation of the immune response may have evolved to provide a well-orchestrated immune defense to ensure survival.


   Acknowledgments
 
We thank Janet Duncan for technical assistance and McKay Brown for expert technical advice. We are also grateful to Greg Wiens and Sarah Coste for critical review of the manuscript and Susan Stevens for insightful discussion.


   Footnotes
 
1 This work is supported by Grants MH55722-04 (to M.P.S.-P.) and AI14985-21 (to M.B.R.) from the National Institutes of Health. Back

2 Current address: Whitehead Institute for Biomedical Research, Cambridge, MA 02142. Back

3 Address correspondence and reprint requests to Dr. Mary P. Stenzel-Poore, Oregon Health Sciences University, Department of Molecular Microbiology and Immunology, 3181 Southwest Sam Jackson Park Road, L220, Portland, OR 97201-3098. Back

4 Abbreviations used in this paper: CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone; HPA, hypothalamic-pituitary-adrenal; tg, transgenic; CORT, corticosterone; DP, double positive; WT, wild type; PC, phosphocholine; KLH, keyhole limpet hemocyanin; NPPC, nitrophenyl PC. Back

Received for publication February 22, 2001. Accepted for publication May 1, 2001.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Aird, F., C. V. Clevinger, M. Prystowsky, E. Redei. 1993. Corticotropin-releasing factor mRNA in rat thymus and spleen. Proc. Natl. Acad. Sci. 90:7104.[Abstract/Free Full Text]
  2. Redei, E.. 1992. Immunoreactive and bioactive corticotropin-releasing factor in rat thymus. Neuroendocrinology 55:115.[Medline]
  3. Suda, T., N. Tomori, F. Tozawa, H. Demura, K. Shizume, T. Mouri, Y. Miura, N. Sasano. 1984. Immunoreactive corticotropin-releasing factor in human hypothalamus, adrenal, lung cancer and pheochromocytoma. J. Clin. Endocrinol. Metab. 58:919.[Abstract]
  4. Vale, W., J. Speiss, C. Rivier, J. Rivier. 1981. Characterization of a 41-residue ovine hypothalamic peptide that stimulates secretion of corticotropin and {beta}-endorphin. Science 213:1394.[Free Full Text]
  5. Vale, W., J. Vaughan, M. Perrin. 1997. Corticotropin-releasing factor (CRF) family of ligands and their receptors. Endocrinologist 7:3S.
  6. Turnbull, A. V., C. Rivier. 1997. Corticotropin-releasing factor (CRF) and endocrine responses to stress: CRF receptors, binding protein, and related peptides. Proc. Soc. Exp. Biol. Med. 215:1.[Abstract]
  7. Munck, A., P. M. Guyre. 1991. Glucocorticoids and immune function. R. Ader, and D. L. Felton, and N. Cohen, eds. Psychoneuroimmunology 447.-475. Academic Press, Rochester.
  8. Kapcala, L. P., T. Chautard, R. L. Eskay. 1995. The protective role of the hypothalamic-pituitary-adrenal axis against lethality produced by immune, infectious, and inflammatory stress. Ann. NY Acad. Sci. 771:419.[Abstract]
  9. Dhabhar, F. S., B. S. McEwen. 1996. Stress-induced enhancement of antigen-specific cell-mediated immunity. J. Immunol. 156:2608.[Abstract]
  10. Dhabhar, F. S.. 1998. Stress-induced enhancement of cell-mediated immunity. Ann. NY Acad. Sci. 840:359.[Abstract/Free Full Text]
  11. McGillis, J. P., A. Park, P. Rubin-Fletter, C. Turck, M. F. Dallman, D. G. Payan. 1989. Stimulation of rat B lymphocyte proliferation by corticotropin-releasing factor. J. Neurosci. 23:346.
  12. Singh, V. K.. 1989. Stimulatory effect of corticotropin-releasing neurohormone on human lymphocyte proliferation and interleukin-2 receptor expression. J. Neuroimmunol. 23:257.[Medline]
  13. Leu, S., V. Singh. 1993. Suppression of in vitro antibody production by corticotropin-releasing factor neurohormone. J. Neuroimmunol. 45:23.[Medline]
  14. Karalis, K., H. Sano, J. Redwine, S. Listwak, R. Wilder, G. Chrousos. 1991. Autocrine or paracrine inflammatory actions of corticotropin-releasing hormone in vivo. Science 254:421.[Abstract/Free Full Text]
  15. Wei, E. T., J. G. Kiang, P. Buchan, T. W. Smith. 1986. Corticotrophin-releasing factor inhibits neurogenic plasma extravasation in the rat paw. J. Pharmacol. Exp. Ther. 238:783.[Abstract/Free Full Text]
  16. Turnbull, A. V., W. Vale, C. Rivier. 1996. Urocortin, a corticotropin-releasing factor-related mammalian peptide, inhibits edema due to thermal injury in rats. Eur. J. Pharmacol. 303:213.[Medline]
  17. Singh, V. K., S. C. Leu. 1990. Enhancing effect of corticotropin-releasing factor on the production of interleukin-1 and interleukin-2. Neurosci. Lett. 120:151.[Medline]
  18. Audhya, T., R. Jain, C. Hollander. 1991. Receptor-mediated immuno-modulation by corticotropin-releasing factor. Cell. Immunol. 134:77.[Medline]
  19. Singh, L. K., W. Boucher, X. Pang, R. Letourneau, D. Seretakis, M. Green, T. C. Theoharides. 1999. Potent mast cell degranulation and vascular permeability triggered by urocortin through activation of corticotropin-releasing hormone receptors. J. Pharmacol. Exp. Ther. 288:1349.[Abstract/Free Full Text]
  20. Crofford, L. J., H. Sano, K. Karalis, E. L. Webster, E. A. Goldmuntz, G. P. Chrousos, R. L. Wilder. 1992. Local secretion of corticotropin-releasing hormone in the joints of Lewis rats with inflammatory arthritis. J. Clin. Invest. 90:2555.
  21. Radulovic, M., F. Dautzenberg, S. Sydow, J. Radulovic, J. Spiess. 1999. Corticotropin-releasing factor receptor 1 in mouse spleen: expression after immune stimulation and identification of receptor-bearing cells. J. Immunol. 162:3013.[Abstract/Free Full Text]
  22. Kageyama, K., M. Bradbury, L. Zhao, A. L. Blount, W. W. Vale. 1999. Urocortin messenger ribonucleic acid: Tissue distribution in the rat and regulation in thymus by lipopolysaccharide and glucocorticoids. Endocrinology 140:5651.[Abstract/Free Full Text]
  23. Stenzel-Poore, M. P., V. A. Cameron, J. Vaughan, P. E. Sawchenko, W. Vale. 1992. Development of Cushing’s syndrome in corticotropin-releasing factor transgenic mice. Endocrinology 130:3378.[Abstract]
  24. Vernikos, J., M. F. Dallman, C. Bonner, A. Katzen, J. Shinsako. 1982. Pituitary-adrenal function in rats chronically exposed to cold. Endocrinology 110:413.[Abstract]
  25. Kant, G. J., T. Eggleston, L. Landman-Roberts, C. C. Kenion, G. C. Driver, J. L. Meyerhoff. 1985. Habituation to repeated stress is stressor specific. Pharmacol. Biochem. Behav. 22:631.[Medline]
  26. Heinrichs, S. C., H. Min, S. Tamraz, M. Carmouche, S. A. Boehme, W. W. Vale. 1997. Anti-sexual and anxiogenic behavioral consequences of corticotropin-releasing factor overexpression are centrally mediated. Psychoneuroendocrinology 22:215.[Medline]
  27. Stenzel-Poore, M. P., S. C. Heinrichs, S. Rivest, G. F. Koob, W. W. Vale. 1994. Overproduction of corticotropin-releasing factor in transgenic mice: a genetic model of anxiogenic behavior. J. Neurosci. 14:2579.[Abstract]
  28. Boehme, S. A., A. Gaur, P. D. Crowe, X. J. Liu, S. Tamraz, T. Wong, A. Pahuja, N. Ling, W. Vale, E. B. De Souza, P. J. Conlon. 1997. Immunosuppressive phenotype of corticotropin-releasing factor transgenic mice is reversed by adrenalectomy. Cell. Immunol. 176:103.[Medline]
  29. Stenzel-Poore, M. P., J. E. Duncan, M. B. Rittenberg, A. C. Bakke, S. C. Heinrichs. 1996. CRH overproduction in transgenic mice: behavioral and immune system modulation. Ann. NY Acad. Sci. 780:36.[Medline]
  30. Hardy, R. R., C. E. Carmack, S. A. Shinton, J. D. Kemp, K. Hayakawa. 1991. Resolution and characterization of pro-B and pre-pro-B cell stages in normal mouse bone marrow. J. Exp. Med. 173:1213.[Abstract/Free Full Text]
  31. Merchant, M. S., B. A. Garvey, R. L. Riley. 1996. Autoantibodies inhibit interleukin-7-mediated proliferation and are associated with the age-dependent loss of pre-B cells in autoimmune New Zealand black mice. Blood 87:3289.[Abstract/Free Full Text]
  32. Mertsching, E., U. Grawunder, V. Meyer, T. Rolink, R. Ceredig. 1996. Phenotypic and functional analysis of B lymphopoiesis in interleukin-7-transgenic mice: expansion of pro/pre-B cell number and persistence of B lymphocyte development in lymph nodes and spleen. Eur. J. Immunol. 26:28.[Medline]
  33. Moscatello, K. M., K. L. Biber, D. C. Dempsey, R. Chervenak, R. M. Wolcott. 1998. Characterization of a B cell progenitor present in neonatal bone marrow and spleen but not in adult bone marrow and spleen. J. Immunol. 161:5391.[Abstract/Free Full Text]
  34. Fleming, T. J., M. L. Fleming, T. R. Malek. 1993. Selective expression of Ly-6G on myeloid lineage cells in mouse bone marrow. J. Immunol. 151:2399.[Abstract]
  35. Chang, S. P., M. Brown, M. B. Rittenberg. 1982. Immunologic memory to phosphorylcholine. II. PC-KLH induces two antibody populations that dominate different isotypes. J. Immunol. 128:702.[Abstract]
  36. Labuer, M. S., E. Arzt, G. J. Wiegers, F. Holsboer, J. M. Reul. 1995. Long-term intracerebroventricular corticotropin-releasing hormone administration induces distinct changes in rat splenocyte activation and cytokine expression. Endocrinology 136:2678.[Abstract]
  37. Harnett, W., M. M. Harnett. 1999. Phosphorylcholine: friend or foe of the immune system. Immunol. Today 20:125.[Medline]
  38. Yother, J., C. Forman, B. M. Gray, D. E. Briles. 1982. Protection of mice from infection with Streptococcus pneumoniae by anti-phosphocholine antibody. Infect. Immun. 36:184.[Abstract/Free Full Text]
  39. Briles, D. E., M. Nahm, K. Schroer, J. Davie, P. Baker, J. Kearney, R. Barletta. 1981. Antiphosphocholine antibodies found in normal mouse serum are protective against intravenous infection with type 3 Streptococcus pneumoniae. J. Exp. Med. 153:694.[Abstract/Free Full Text]
  40. Briles, D. E., C. Forman, S. Hudak, J. Claflin. 1982. Anti-phosphocholine antibodies of the T15 idiotype are optimally protective against Streptococcus pneumoniae. J. Exp. Med. 156:1177.[Abstract/Free Full Text]
  41. Briles, D. E., C. Forman, S. Hudak, J. L. Claflin. 1984. The effects of idiotype on the ability of IgG1 anti-phosphorylcholine antibodies to protect mice from fatal infection with Streptococcus pneumoniae. Eur. J. Immunol. 14:1027.[Medline]
  42. McDaniel, L. S., W. H. Benjamin, C. Forman, D. E. Briles. 1984. Blood clearance by anti-phosphocholine antibodies as a mechanism of protection in experimental pneumococcal bacteremia. J. Immunol. 133:3308.[Abstract]
  43. Al-Qaoud, K. M., B. Fleischer, A. Hoerauf. 1998. The xid defect imparts susceptibility to experimental murine filariosis: association with a lack of antibody and IL-10 production by B cells in response to phosphorylcholine. Int. Immunol. 10:17.[Abstract/Free Full Text]
  44. Ponnappan, U., B. Cinader, V. Gerber, K. Blaser. 1992. Polymorphism of age-related changes in the antibody response to the hapten phosphorylcholine. Immunol. Invest. 21:637.[Medline]
  45. Brown, E. J., S. W. Hosea, C. H. Hammer, C. G. Burch, M. M. Frank. 1982. A quantitative analysis of the interactions of antipneumococcal antibody and complement in experimental pneumococcal bacteremia. J. Clin. Invest. 69:85.
  46. Fischer, R. T., D. L. Longo, J. J. Kenny. 1995. A novel phosphocholine antigen protects both normal and X-linked immune deficient mice against Streptococcus pneumoniae. J. Immunol. 154:3373.[Abstract]
  47. Wallick, S., J. L. Claflin, D. E. Briles. 1983. Resistance to Streptococcus pneumoniae is induced by a phosphocholine-protein conjugate. J. Immunol. 130:2871.[Abstract]
  48. Gordon, D. L., G. M. Johnson, M. K. Hostetter. 1986. Ligand-receptor interactions in the phagocytosis of virulent Streptococcus pneumoniae by polymorphonuclear leukocytes. J. Infect. Dis. 154:619.[Medline]
  49. Noya, F. J. D., C. J. Baker, M. S. Edwards. 1993. Neutrophil Fc receptor participation in phagocytosis of type III group B streptococci. Infect. Immun. 61:1415.[Abstract/Free Full Text]
  50. Hall, M. A., M. E. Hickman, C. J. Baker, M. S. Edwards. 1994. Complement and antibody in neutrophil-mediated killing of type V group B streptococcus. J. Infect. Dis. 170:88.[Medline]
  51. Hart, P. H., L. K. Spencer, A. Nikoloutsopoulos, A. F. Lopez, M. A. Vada, P. J. McDonald, J. J. Finlay-Jones. 1986. Role of cell surface receptors in the regulation of intracellular killing of bacteria by murine peritoneal exudate neutrophils. Infect. Immun. 52:245.[Abstract/Free Full Text]
  52. Huizinga, T. W. J., F. vanKemenade, L. Koenderman, K. M. Dolman, A. E. G. von dem Borne, P. A. T. Tetteroo, D. Roos. 1989. The 40-kDa receptor (FcR11) on human neutrophils is essential for the IgG-induced respiratory burst and IgG-induced phagocytosis. J. Immunol. 142:2365.[Abstract]
  53. McEwen, B. S.. 1998. Protective and damaging effects of stress mediators. N. Engl. J. Med. 338:171.[Free Full Text]
  54. Franco, P., O. Marelli, D. Lattuada, V. Locatelli, D. Cocchi, E. E. Muller. 1990. Influence of growth hormone on the immunosuppressive effect of prednisolone in mice. Acta Endocrinol. 123:339.
  55. Dumont, F., R. Barrois. 1977. Electrokinetic properties and mitogen responsiveness of mouse splenic B and T lymphocytes following hydrocortisone treatment. Int. Arch. Allergy Appl. Immunol. 53:293.[Medline]
  56. Homo, F., D. Duval, J. Hatzfeld, C. Evrard. 1980. Glucocorticoid sensitive and resistant cell populations in the mouse thymus. J. Steroid Biochem. 13:135.[Medline]
  57. Blomgren, H., B. Andersson. 1971. Characteristics of the immunocompetent cells in the mouse thymus: cell populations changes during corticosterone-induced atrophy and subsequent regeneration. Cell. Immunol. 1:545.
  58. Garvy, B. A., L. E. King, W. G. Telford, L. A. Morford, P. J. Fraker. 1993. Chronic elevation of plasma corticosterone causes reductions in the number of cycling cells of the B lineage in murine bone marrow and induces apoptosis. Immunology 80:587.[Medline]
  59. Cidlowski, J. A., K. L. King, R. B. Evans-Storms, J. W. Montague, C. D. Bortner, F. M. Hughes. 1996. The biochemistry and molecular biology of glucocorticoid-induced apoptosis in the immune system. Recent Prog. Hormone Res. 51:457.
  60. Garvy, B. A., W. G. Telford, L. E. King, P. J. Fraker. 1993. Glucocorticoids and irradiation-induced apoptosis in normal murine bone marrow B-lineage lymphocytes as determined by flow cytometry. Immunology 79:270.[Medline]
  61. Voetberg, B. J., B. A. Garvy, H. K. Mayer, L. E. King, P. J. Fraker. 1994. Apoptosis accompanies a change in the phenotypic distribution and functional capacity of murine bone marrow B-cells chronically exposed to prednisolone. Clin. Immunol. Immunopathol. 71:190.[Medline]
  62. Rey, A. d., H. Besedovsky, E. Sorkin. 1984. Endogenous blood levels of corticosterone control the immunologic cell mass. J. Immunol. 133:572.[Abstract]
  63. Vacchio, M. S., V. Papadopoulos, J. D. Ashwell. 1994. Steroid production in the thymus: implications for thymocyte selection. J. Exp. Med. 179:1835.[Abstract/Free Full Text]
  64. Vacchio, M. S., J. D. Ashwell. 1997. Thymus-derived glucocorticoids regulate antigen-specific positive selection. J. Exp. Med. 185:2033.[Abstract/Free Full Text]
  65. Purton, J. F., R. L. Boyd, T. J. Cole, D. I. Godfrey. 2000. Intrathymic T cell development and selection proceeds normally in the absence of glucocorticoid receptor signaling. Immunity 13:179.[Medline]
  66. Merino, R., L. Ding, D. J. Veis, S. J. Korsmeyer, G. Nunez. 1994. Developmental regulation of the Bcl-2 protein and susceptibility to cell death in B lymphocytes. EMBO J. 13:683.[Medline]
  67. Aebischer, I., M. R. Stampfli, A. Zurcher, S. Miescher, A. Urwyler, B. Frey, T. Luger, R. R. White, B. M. Stadler. 1994. Neuropeptides are potent modulators of human in vitro immunoglobulin E synthesis. Eur. J. Immunol. 24:1908.[Medline]
  68. Bost, K. L., B. L. Clarke, J. Xu, H. Kiyono, J. R. McGhee, D. Pascual. 1990. Modulation of IgM secretion and H chain mRNA expression in CH12.LX.C4.5F5 B cells by adrenocorticotropic hormone. J. Immunol. 145:4326.[Abstract]
  69. Stavnezer, J.. 1996. Antibody class switching. Adv. Immunol. 61:79.[Medline]
  70. Stavnezer, J.. 1999. Molecular processes that regulate class switching. Curr. Top. Microbiol. Immunol. 245:127.
  71. Alonso DeVelasco, E., B. A. T. Dekker, A. F. M. Verheul, R. G. Feldman, J. Verhoef, H. Snippe. 1995. Anti-polysaccharide immunoglobulin isotype levels and opsonic activity of antisera: relationships with protection against Streptococcus pneumoniae infection in mice. J. Infect. Dis. 172:562.[Medline]
  72. Boes, M., A. P. Prodeus, T. Schmidt, M. C. Carroll, J. Chen. 1998. A critical role of natural immunoglobulin M in immediate defense against systemic bacterial infection. J. Exp. Med. 188:2381.[Abstract/Free Full Text]
  73. Baumgarth, N., O. C. Herman, G. C. Jager, L. E. Brown, L. A. Herzenberg, J. Chen. 2000. B-1 and B-2 cell-derived immunoglobulin M antibodies are nonredundant components of the protective response to influenza virus infection. J. Exp. Med. 192:271.[Abstract/Free Full Text]
  74. Ochsenbein, A. F., T. Fehr, C. Lutz, M. Suter, F. Brombacher, H. Hengartner, R. M. Zinkernagel. 1999. Control of early viral and bacterial distribution and disease by natural antibodies. Science 286:2156.[Abstract/Free Full Text]
  75. Shibuya, A., N. Sakamoto, Y. Shimizu, K. Shibuya, M. Osawa, T. Hiroyama, H. J. Eyre, G. R. Sutherland, Y. Endo, T. Fujita, T. Miyabayashi, S. Sakano, T. Tsuji, E. Nakayama, J. H. Phillips, L. L. Lanier, H. Nakauchi. 2000. Fc{alpha}/µ receptor mediates endocytosis of IgM-coated microbes. Nat. Immunol. 1:441.[Medline]
  76. Meagher, L. C., J. M. Cousin, J. R. Seckl, C. Haslett. 1996. Opposing effects of glucocorticoids on the rate of apoptosis in neutrophilic and eosinophilic granulocytes. J. Immunol. 156:4422.[Abstract]
  77. Nakagawa, M., T. Takeshi, Y. D’yachkova, G. P. Bondy, J. C. Hogg, S. F. van Eeden. 1998. Glucocorticoid-induced granulocytosis: contribution of marrow release and demargination of intravascular granulocytes. Circulation 98:2307.[Abstract/Free Full Text]
  78. Cox, G.. 1995. Glucocorticoid treatment inhibits apoptosis in human neutrophils. J. Immunol. 154:4719.[Abstract]
  79. Liles, C., D. C. Dale, S. J. Klebanoff. 1995. Glucocorticoids inhibit apoptosis of human neutrophils. Blood 86:3181.[Abstract/Free Full Text]
  80. Forner, M. A., C. Barriga, A. B. Rodriguez, E. Ortega. 1995. A study of the role of corticosterone as a mediator in exercise-induced stimulation of murine macrophage phagocytosis. J. Physiol. 488:789.[Medline]
  81. Ortega, E., M. A. Forner, C. Barriga, M. de la Fuente. 1993. Effect of age and of swimming-induced stress on the phagocytic capacity of peritoneal macrophages from mice. Mech. Ageing Dev. 70:53.[Medline]
  82. Marotti, T., J. Gabrilovac, S. Rabatic, L. Smejkal-Jagar, B. Rocic, H. Haberstock. 1996. Met-enkephalin modulates stress-induced alterations of the immune response in mice. Pharmacol. Biochem. Behav. 54:277.[Medline]
  83. Lyte, M., S. G. Nelson, B. Baissa. 1990. Examination of the neuroendocrine basis for the social conflict-induced enhancement of immunity in mice. Physiol. Behav. 48:685.[Medline]
  84. Freischlag, J. A., M. D. Colburn, W. J. Quinones-Baldrich, W. S. Moore. 1992. Alteration of neutrophil (PMN) function by heparin, dexamethasone, and enalapril. J. Surg. Res. 52:523.[Medline]
  85. Shurin, M. R., A. Kusnecov, E. Hamill, S. Kaplan, B. S. Rabin. 1994. Stress-induced alteration of polymorphonuclear leukocyte function in rats. Brain Behav. Immun. 8:163.[Medline]
  86. Trowald-Wigh, G., L. Hakansson, A. Johannisson, L. E. Edqvist. 1998. The effect of prednisolone on canine neutrophil function: in vivo and in vitro studies. Acta Vet. Scand. 39:201.[Medline]
  87. Archana, R., A. Namasivayam. 1999. The effect of acute noise stress on neutrophil functions. Indian J. Pharmacol. 43:491.
  88. Lyte, M., S. G. Nelson, M. L. Thompson. 1990. Innate and adpative immune responses in a social conflict paradigm. Clin. Immunol. Immunopathol. 57:137.[Medline]
  89. Edwards, K. M., H. Gewurz, T. F. Lint, C. Mold. 1982. A role for C-reactive protein in the complement-mediated stimulation of human neutrophils by type 27 Streptococcus pneumoniae. J. Immunol. 128:2493.[Abstract]
  90. Zach, T. L., V. A. Herrman, L. D. Hill, M. P. Leuschen. 1993. Effect of steroids on the synthesis of complement C3 in a human alveolar epithelial cell line. Exp. Lung Res. 19:603.[Medline]
  91. Zach, T. L., L. D. Hill, V. A. Herrman, M. P. Leuschen, M. K. Hostetter. 1992. Effect of glucocorticoids on C3 gene expression by the A549 human pulmonary epithelial cell line. J. Immunol. 148:3964.[Abstract]
  92. Trinder, P. K. E., D. Faust, F. Petry, M. Loos. 1995. Modulation of mRNA expression and secretion of C1q in mouse macrophages by anti-inflammatory drugs and cAMP: evidence for the partial involvement of a pathway that includes cyclooxygenase, prostaglandin E2 and adenylate cyclase. Immunology 84:638.[Medline]
  93. Hill, L. D., L. Sun, M. P. Leuschen, T. L. Zach. 1993. C3 synthesis by A549 alveolar epithelial cells is increased by interferon-{gamma} and dexamethasone. Immunology 79:236.[Medline]
  94. Horowitz, J., J. E. Volanakis, D. E. Briles. 1987. Blood clearance of Streptococcus pneumoniae by C-reactive protein. J. Immunol. 138:2598.[Abstract]
  95. Radulovic, M., C. Weber, J. Spiess. 2000. The effect of acute immobilization stress on the abundance of corticotropin-releasing factor receptor in lymphoid organs. J. Neuroimmunol. 103:153.[Medline]
  96. Webster, E. L., E. B. DeSouza. 1988. Corticotropin-releasing factor receptors in mouse spleen: identification, autoradiographic localization, and regulation by divalent cations and guanine nucleotides. Endocrinology 122:609.[Abstract]
  97. Koshida, H., Y. Kotake. 1994. Corticotropin-releasing hormone enhances the superoxide anion production of rabbit peritoneal macrophages stimulated with N-formyl-methionyl-leucyl-phenylalanine. Life Sci. 54:539.[Medline]



This article has been cited by other articles:


Home page
 EndocrinologyHome page
A. Kariagina, D. Romanenko, S.-G. Ren, and V. Chesnokova
Hypothalamic-Pituitary Cytokine Network
Endocrinology, January 1, 2004; 145(1): 104 - 112.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
A. Moraska, J. Campisi, K. T. Nguyen, S. F. Maier, L. R. Watkins, and M. Fleshner
Elevated IL-1beta contributes to antibody suppression produced by stress
J Appl Physiol, July 1, 2002; 93(1): 207 - 215.
[Abstract] [Full Text] [PDF]

Home page
 J. Immunol.Home page
P. Mancuso, A. Gottschalk, S. M. Phare, M. Peters-Golden, N. W. Lukacs, and G. B. Huffnagle
Leptin-Deficient Mice Exhibit Impaired Host Defense in Gram-Negative Pneumonia
J. Immunol., April 15, 2002; 168(8): 4018 - 4024.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow