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Departments of
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Kinesiology and Applied Physiology and
Psychology, University of Colorado, Boulder, CO 80309
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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, but not the anti-KLH IgG1, response.
Given that IFN- is an important regulator of the IgM to IgG2a
switch, it is possible that the small rise in GC found 4–7 days after
KLH facilitates IgG2a isotype switching. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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These studies may have limited relevance to the role of GCs during normal in vivo immune responses for several reasons. First, the actions of DEX and endogenous GCs are quite different, such that DEX bypasses a number of physiological buffering mechanisms that limit the impact of endogenous GCs on target tissues (6, 7, 8). Second, pharmacological and physiological levels of GCs may produce very different outcomes. In their extensive review, Spencer et al. (1) concluded that many physiological processes are inhibited by high doses, but facilitated by physiological levels, of GCs. Finally, in vitro and in vivo effects are frequently different. GCs often function by altering the response of a cell to other signals, and these other signals may not be present in vitro. In addition, GC actions on a target in vivo are sometimes mediated indirectly via action on a different cell type, which may not be present in vitro (1)
Physiological levels of endogenous GCs can have important positive effects on various aspects of immune responding. With regard to acquired immunity, a number of in vivo processes related to T cell function are facilitated (2). For example, in vivo administration of stress levels of endogenous GCs before sensitizing Ag facilitates the largely T cell-mediated delayed-type hypersensitivity response (9), as does the administration of GCs before the delayed-type hypersensitivity challenge (10). These effects on the delayed-type hypersensitivity response are caused by GC regulation of cell trafficking. In addition, GCs are implicated in the regulation of Th1/Th2 balance, such that GCs in vivo can reduce Th1 cytokines and increase Th2 cytokines (11).
Less is known about the role that endogenous GCs might play in mediating B cell function and the production of Ab. Low levels of GCs are necessary in cell culture to obtain optimal in vitro Ab production (12). However, the literature is contradictory beyond this permissive effect. Although some studies have found a positive correlation between endogenous stress-induced GCs increases and Ab production (13), other experiments have yielded a negative correlation between endogenous GC levels and splenic Ab-producing cells (14). In addition, administration of GCs has been reported to either increase (15) or have no effect (16) on plasma Ab levels.
A small number of studies have examined the effects of adrenalectomy (ADX) on the B cell response to Ag. However, we have not found a study that examined the impact of GC replacement in ADX subjects, so it is difficult to attribute any effects that were found to GCs rather than to other adrenal products. Furthermore, the few experiments that have been reported have typically examined only the plaque-forming response of splenic B cells 3–4 days after Ag presentation. The development of a primary Ab response is a complex process that extends over several weeks. Many factors that influence Ab production occur at a time later than 3–4 days after Ag administration. The cytokine-facilitated IgM to IgG switch, for example, often occurs 5–8 days after in vivo Ag challenge. Thus, any role that GC might play in modulating these events that occur >3 or 4 days after Ag is unexplored. Interestingly, a small rise in plasma corticosterone (CORT) has been reported to occur 5–7 days after the administration of both sheep erythrocytes (17) and keyhole limpet hemocyanin (KLH) (18). Whether this small rise in CORT 5–7 days after Ag is important for Ab formation is unknown. Therefore, the following studies will examine the potential role of endogenous CORT in generation of an in vivo Ag-specific Ab response and test the impact of DEX vs CORT on the generation of this response.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Adult male Harlan Sprague-Dawley specific-pathogen free rats (275–300 g) were used in all experiments. All subjects were maintained on a 12-h light, 12-h dark cycle (lights on, 0600–1800 h) in a viral-free environment. Both the colony room as well as the treatment room were equipped with the BioBubble air filtration system (model M501A) to maintain virus-free conditions. Standard rat chow and water were freely available. Subjects were allowed to acclimate to the colony for 14 days before experimentation began. They were handled briefly once daily for 3 days just before the start of the experiment. Animals were individually housed in metal hanging cages. Colony room temperature was maintained at 22–23°C. The care and use of the animals were in accordance with protocols approved by the University of Colorado institutional animal care and use committee.
Immunization and Ab measurement
Rats were immunized i.p. with 200 µg of soluble KLH (lot 001738, Calbiochem, La Jolla, CA; in 50% glycerol) in 0.5 ml of sterile saline. Tail vein blood samples were quickly collected (within 2 min of touching the cage) by gently wrapping the rats in a small towel and lightly restraining them using a Velcro strapping apparatus. The tail was exposed, a small nick was made with a scalpel (no. 15 blade), and the blood sample (300 µl) was quickly milked from the tail vein. Serum levels of anti-KLH IgM and IgG were determined using an ELISA. The details of the ELISA procedure (using alkaline phosphatase) for anti-KLH IgM and anti-KLH IgG have been presented previously (16, 19).
Anti-KLH IgM was measured on days 5, 7, 10, 14, 21, and 28 after immunization, and anti-KLH IgG was measured on days 7, 10, 14, 21, and 28 after KLH immunization. This was done because the IgG response before day 7 is negligible. Each anti-KLH IgM and anti-KLH IgG sample was calculated as the proportion of its plate that was positive, which is very nearly equal to 1.0 absorption unit. This is a standard transformation for data reported using ELISA (20). Data were presented for samples assayed at a 1/200 dilution for IgM and a 1/6000 dilution for IgG. These dilutions were chosen so that samples fell within the linear range of the plate reader. Observed differences were consistent across dilutions.
Adrenalectomy
Bilateral ADX were aseptically performed under halothane anesthesia (Halocarbon Laboratories, River Edge, NJ). All removed tissue was examined to ensure complete removal of the adrenal gland. Sham-operated animals received the identical procedure, except that the adrenal glands were gently manipulated with forceps, but were not removed. All ADX rats were maintained with 0.5% saline either with or without basal CORT replacement.
Basal CORT replacement
In studies involving basal CORT replacement, steroid replacement began immediately after surgery. ADX animals received CORT replacement in their drinking water because this method has been shown to mimic the normal circadian pattern of CORT secretion and to normalize thymic hypertrophy (21). CORT (Sigma, St. Louis, MO) was initially dissolved in ethyl alcohol (ETOH) and diluted to a final concentration of 25.0 µg/ml in 0.2% ETOH. CORT-water also contained 0.5% saline. Sham animals received drinking water containing 0.2% ETOH. Animals were allowed 3 wk to recover after surgery before additional experimental manipulation.
CORT receptor blockade
GC receptor (GCr) antagonists were injected s.c. 5 and 7 days
after KLH. RU28386 (Roussel-UCLAF, Romainville, France; 
-GCr type I)
and RU40555 (Roussel-UCLAF, -GRr type II) antagonists were dissolved
in propylene glycol (1,2-propandediol, Fisher Scientific, Pittsburgh,
PA) at doses of 50.0 mg/kg/2 ml and 30.0 mg/kg/ml, respectively. These
doses have been previously reported to effectively antagonize CORT
binding to both type I and type II receptors (22).
Acute CORT addition
Stenzle-Poore et al. (18) previously reported a small, but statistically significant, increase in circulating CORT levels 5–7 days after antigenic challenge. To test whether this increase is necessary to produce optimal levels of anti-KLH Ig, ADX rats were given basal CORT replacement in the drinking water. Acute increases in CORT were created by s.c. injecting 1.0 mg/kg/ml of CORT (Sigma) dissolved in propylene glycol (1,2-propandediol, Fisher Scientific) on days 5 and 7 after KLH. Rats receiving no acute CORT received a vehicle injection. The resulting blood levels of CORT were verified in a separate group of rats. Rats (n = 15) received ADX surgery and were placed on basal CORT replacement in the drinking water. After 3 wk of recovery, rats were s.c. injected with CORT (1.0 mg/kg/ml). Tail vein blood samples were collected before injection (baseline) and 30, 90, 150, and 300 min after injection.
Endogenous CORT increases after i.p. KLH
The prior study of CORT levels after i.p. KLH used the Ag phosphocholine-KLH in CFA (18). The present studies used nonhaptenated KLH without the addition of adjuvant and also used a lower dose. Thus, rats (n = 12/group) were injected with either KLH (200 µg i.p.) or saline. Tail vein blood samples were taken before injection (baseline) and again 1, 3, and 7 days after immunization. All samples were collected between 0900 and 1000 h. A single time point during the day was chosen for study because the intent was to verify whether a CORT rise does or does not occur with the present Ag, not to characterize the nature of the increase.
CORT assay
Serum levels of total CORT were measured using RIA procedures recommended by Sigma (intra- and interassay CVs, <10%). CORT Ab was purchased from Sigma (C-8784). Blood samples (100 µl) were taken from the tail vein and allowed to clot, and serum was removed and frozen at -20°C until later analysis.
Basal CORT replacement verification
To verify the efficacy of the basal CORT replacement in the drinking water, rats were adrenalectomized or received sham surgery as described above. After recovery from anesthesia, rats were returned to their home cages, and ADX rats were maintained on water that contained 0.5% saline and 0.2% ETOH with (n = 11) or without (n = 5) 25.0 µg/ml of CORT. Sham animals (n = 5) received drinking water containing 0.2% ETOH. Animals were allowed 3 wk to recover after surgery before additional experimental manipulation. Serum CORT levels were verified in the ADX rats only. Three weeks after surgery, blood samples (200 µl) were taken from the tail vein of basal CORT-replaced (n = 11) and nonreplaced (n = 5) rats.
Effect of DEX on the in vivo Ab response
To demonstrate the uniquely immunosuppressive effect of DEX (Sigma) on the in vivo anti-KLH Ig response, rats (n = 6/grp) were immunized with KLH (as previously described) and then injected s.c. with either DEX (2.5 mg/kg) or saline vehicle. Blood samples were taken from the tail vein on days 5, 7, 14, 21, and 28 after KLH. Anti-KLH IgM (1/400) and anti-KLH IgG (1/6000) levels were measured using ELISA (as previously described).
Effect of GCr blockade on anti-KLH IgG1 and IgG2a
To begin to reveal a potential mechanism for the effect of GCr blockade on anti-KLH Ig, anti-KLH IgG isotypes (IgG1 and IgG2a) were measured in the serum taken from the CORT receptor blockade experiment described above. The details of these ELISAs have been published previously (16).
Effect of GCr blockade on splenic IFN-
Rats (n = 8/group) were injected s.c. with either RU386 (10
mg/kg, Mifepristone, RBI, Natick, MA) or vehicle (propylene glycol,
1,2-propandediol, Fisher Scientific). RU486 is a type II GCr
antagonist. The Roussal-UCLAF compounds RU28386 and RU40555 were not
available for experimental study at this time. Importantly, we have
previously reported that RU486 produces a similar (albeit smaller)
suppressive effect on anti-KLH IgM, IgG, and IgG2a as that of
RU28386 and RU40555 treatment (16). RU486 was also isotype
specific, in that it reduced anti-KLH IgG2a and not anti-KLH
IgG1 (16). One hour after RU486, rats were immunized i.p.
with KLH as described above. Four days after KLH, all rats were
sacrificed via brief ether exposure and cervical dislocation. Spleens
were removed, placed in Ischove’s medium containing 1.0%
penicillin/streptomycin, and put on ice. After all dissections were
complete, spleens were hand-homogenized, and cell concentrations were
determined using a Coulter counter (Hialeah, FL). Cells were then
placed in culture medium at a concentration of 10.0 x
106 cell/ml/well. Culture medium was comprised of
Ischove’s supplemented with 10% FCS (Life Technologies), 1%
L-glutamine (Life Technologies), and 1% Pen/Strep (Life
Technologies). Cells were either unstimulated or stimulated with Con A
(5.0 µg/well; Sigma) and placed in culture for 48 h in 5%
CO2 at 37°C. Supernatants were collected and
assayed for IFN- using rat-specific ELISA (BioSource, Camarillo,
CA)
Statistical analysis
All data were analyzed using repeated measures ANOVA. Statistical significance is set at p < 0.05. Post-hoc group differences were tested using Fisher’s protected least significant difference test.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Rats (n = 10/grp) were given ADX, sham surgery, or
no surgery. Half of the ADX rats received CORT replacement in their
drinking water, while the other half received only saline added to
their drinking water. Six weeks after surgery, all animals were
immunized with KLH, and blood samples were collected on days 5, 7, 10,
14, and 21 after immunization. Anti-KLH IgM and IgG in these groups are
shown in Fig. 1
. In agreement with
previous reports (16, 19) anti-KLH IgM levels were
already high 5 days after Ag administration and declined thereafter.
ADX reduced blood levels of anti-KLH IgM across the period of
measurement, and this reduction was largely, but not entirely, restored
by the replacement of basal CORT. Sham surgery by itself had no effect
on anti-KLH IgM. Sham surgery did not impact the anti-KLH IgM
response compared with that of the no surgery controls. A repeated
measures ANOVA (4 x 4) revealed a significant effect of time
after KLH (F(3,102) = 49.7; p = 0.0001)
and a significant main effect of group (F(3,34) = 3.7;
p = 0.02). Also as expected, anti-KLH IgG Ab was at
a low level 7 days after Ag administration and increased over the
period of testing. However, anti-KLH IgG revealed a somewhat
different pattern than IgM. ADX also reduced anti-KLH IgG levels,
and this effect was maintained for the 21 days of measurement. In
contrast to the results for IgM, basal CORT replacement did not reduce
the decrement in IgG. Sham surgery did not impact the anti-KLH IgG
response compared with that of the no surgery controls. A repeated
measures ANOVA (4 x 4) revealed a significant effect of time
after KLH (F(3,102) = 86.8; p = 0.0001)
and a significant group x time interaction
(F(9,102) = 2.8; p = 0.006). Thus,
basal CORT replacement partially restores anti-KLH IgM, but not
anti-KLH IgG.
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ADX removes CORT during all phases of the processes that generate
Ab. To begin to explore whether the CORT rise that occurs 5–7 days
after Ag might play a role, GCr were blocked on days 5 and 7 in non-ADX
subjects (n = 10/group) after immunization with KLH.
Both the type I and the type II receptors were blocked with a drug
combination (RU40555 plus RU28318) because there was no a priori reason
to selectively focus on one or the other. Day 5 blood samples were not
collected in this study. The results of administering RU40555 and
RU28318 on days 5 and 7 after KLH on anti-KLH Igs on days 7–28 are
shown in Fig. 2. Anti-KLH IgM was
profoundly reduced even on day 7. The blood sample was taken before the
day 7 injection, so this reduction reflects the impact of the single
injection on day 5. The interference with anti-KLH IgM production
was maintained for the 28 days of testing. A repeated measures ANOVA
(2 x 4) revealed a significant effect of drug
(F(1,19) = 12.1; p = 0.0025) and a
significant effect of time after KLH (F(4,76) = 70.9;
p = 0.0001). GCr blockade on days 5 and 7 reduced
anti-KLH IgG for the 28 days of measurement. A repeated measures
ANOVA (2 x 4) revealed a significant effect of drug
(F(1,19) = 4.3; p = 0.05) and a
significant effect of time after KLH (F(4,76) = 70.9;
p = 0.0001). Therefore, pharmacological blockade of
type I and type II GCr reduces both anti-KLH IgM and
anti-KLH IgG.
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The receptor blockade used in the experiment above would be
expected to reduce or eliminate the effects of both basal CORT for the
period of antagonist action as well as the CORT rise above baseline
that occurs at this time. If the rise in CORT above baseline that
occurs 5–7 days after Ag is the important feature, then administering
an injection of CORT to ADX, basal CORT-replaced subjects at this time
should restore Ab production. Fig. 3
shows the CORT profile produced by the 1.0 mg/kg s.c. dose chosen for
this experiment. It produced an increase in blood levels to 14.0
µg/dl, and blood levels had returned nearly to normal levels within
5 h (Fig. 3). These levels are lower than those induced by
stressors such as tail shock studied in the laboratory
(23), but are higher than that produced by KLH (see Fig. 4; 
7.0 µg/dl) (18).
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ADX once again reduced anti-KLH IgM as in the experiment described
above. Although basal CORT replacement and CORT injection did increase
anti-KLH above the results with ADX, they did not restore the IgM
response to sham levels. A repeated measures ANOVA (3 x 5)
revealed a significant effect of time after KLH
(F(5,145) = 17.3; p = 0.0001) and a
significant group x time interaction (F(10,145) =
2.3; p = 0.01). However, the pattern for anti-IgG
was quite clear. ADX again strongly reduced anti-KLH IgG.
Interestingly, the combination of basal CORT replacement and CORT
injections on days 5 and 7 fully restored anti-KLH IgG production.
A repeated measures ANOVA (2 x 5) revealed a significant effect
of time after KLH (F(4,116) = 54.8; p =
0.0001) and a significant group x time interaction
(F(8,116) = 2.0; p = 0.0466).
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As presented in Fig. 4
, CORT levels were indeed elevated 7 days
after Ag administration. Although the rise was small, it was reliable
and emerged consistently in other experiments. A repeated measures
ANOVA (2 x 5) revealed a significant effect of time after KLH
(F(4,88) = 4.2; p = 0.0036) and a
significant group x time interaction (F(4,88) =
3.5; p = 0.0110).
Basal CORT replacement verification
To verify the efficacy of the basal CORT replacement regimen used in these experiments, we tested whether CORT replacement would normalize thymic hypertrophy produced by ADX and would reproduce the circadian peak and nadir of serum CORT. Basal CORT in the drinking water completely eliminated the thymic hypertrophy produced by ADX (data not shown). A three-group ANOVA revealed a significant effect of group (F(2,18) = 11.6; p = 0.0001). Fisher’s protected least significant difference test post-hoc analyses revealed a significant difference between ADX plus CORT and ADX plus saline groups (p < 0.01), but no difference between ADX plus CORT and sham-treated animals. Basal CORT replacement increased nadir CORT levels and produced a circadian peak of CORT in the serum (data not shown). For the ADX plus saline animals, basal levels of CORT were 0.975 ± 0.3 µg/dl (mean ± SEM) at 1000 h and 0.800 ± 0.3 µg/dl at 2200 h. For the ADX plus CORT animals, basal levels of CORT were 2.6 ± 0.6 µg/dl at 1000 h and 7.8 ± 0.9 µg/dl at 2200 h. A repeated measures ANOVA (2 x 2) revealed a significant effect of group (F(1,13) = 41.3; p < 0.0001) and a significant group x time interaction (F(1,13) = 4.7; p < 0.04).
Effect of DEX on the in vivo Ab response
Fig. 6 depicts the immunosuppressive
effect of DEX on anti-KLH IgM and anti-KLH IgG. Clearly, 2.5
mg/kg of DEX at the time of KLH immunization nearly eliminated the Ig
response. These observations are supported by a significant effect of
drug on both anti-KLH IgM (F(1,10) = 53.1;
p = 0.0001) and anti-KLH IgG
(F(1,10) = 35.1; p = 0.0001).
Importantly, an equal dose of CORT has been previously reported by our
laboratory to be completely without effect on the in vivo anti-KLH
Ig response (16).
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Clearly, as shown in Fig. 7, rats
treated with the GCr type I antagonist (RU28318) and the GCr type II
antagonist (RU40555) made less anti-KLH IgG2a
(F(1,57) = 4.2; p = 0.05), but not
anti-KLH IgG1 (p > 0.05).
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As shown in Fig. 7, GCr blockade reduced anti-KLH IgG2a, but
not anti-KLH IgG1. Because IFN- plays an important role in
stimulating the IgM to IgG2a switch (24), splenic IFN-
production was measured in KLH-immunized rats 4 days after Ag
treatment. As shown in Fig. 8, rats that
received the GCIIr antagonist (RU486) at the time of KLH immunization
had reduced splenic IFN- levels (F(1,14) = 13.2;
p = 0.002). The cells were not restimulated in culture;
therefore, the IFN- levels produced were the result of KLH
immunization. Con A-stimulated IFN- levels were not reduced in the
GCIIr antagonist-treated rats (RU486, 33,131 ± 1,489 pg/ml;
vehicle, 27,797 ± 4374 pg/ml). This suggests that GCr antagonism
suppressed the KLH-specific, and not the total, IFN- response.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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ADX reduced circulating levels of both anti-KLH IgM and anti-KLH IgG. Basal CORT replacement restored most, but not all, of the anti-KLH IgM response, but had no effect on the anti-KLH IgG reduction produced by ADX. Thus, basal CORT would appear to play a role in the generation of the initial Ig developed to KLH, namely IgM. An injection of GCr antagonists to intact animals on day 5 following Ag reduced anti-KLH IgM measured on day 7. Furthermore, GCr blockade on days 5 and 7 after KLH interfered with the IgM response for the entire 28-day measurement period. Thus, even a relatively brief blockade of CORT several days after antigenic challenge can reduce the primary IgM Ab response for the entire duration of the response. It cannot be concluded whether the GCr blockade impacted anti-KLH IgM because it reduced basal GCr activation or impacted the CORT rise during the immune response. However, it is reasonable to speculate that the ADX-induced reduction in anti-KLH IgM was due to basal CORT for several reasons. First, basal CORT replacement reduced the magnitude of the ADX-induced IgM decrement. Second, the endogenous CORT rise did not appear until 7 days after KLH. Third, CORT receptor antagonist injection on day 5 reduced anti-KLH-IgM on day 7.
In contrast, basal CORT replacement had no effect on the anti-KLH IgG reduction produced by ADX. However, the addition of CORT injections on days 5 and 7 to basal CORT replacement, fully restored the anti-KLH IgG response in ADX subjects. Furthermore, GCr blockade on days 5 and 7 reduced anti-KLH IgG for the 28-day period of the experiment. Thus, it would seem that the rise in CORT above baseline that occurs 5–7 days after Ag is of critical importance for the in vivo production of IgG to Ag.
The data suggest that basal CORT is important for the initial IgM response to KLH, and the CORT rise 5–7 days after primary immunization is important for IgG development. Although the precise mechanisms for the regulatory role of CORT in Ig responses are not yet clear, there is evidence from in vitro studies that suggest several possibilities. First, basal CORT may be important for the anti-KLH IgM response because CORT up-regulates a number of cytokine receptors on monocytes and T cells. For example, GCs can potentiate IL-2 induction of IL-2R mRNA in several T cell lines (25), and physiological levels of GCs have been reported to increase the binding of IL-1 to peripheral blood monocytes in vitro (26). Cytokines such as IL-1 and IL-2 are involved in the initial proliferation and development of Ag-specific T cells, and so basal CORT may be important in the early stages of the development of cells that will provide T cell help in developing plasma cells.
Basal CORT replacement normalized thymus weight, but not anti-KLH IgM. This observation is not unexpected, because the mechanisms of CORT action are believed to be different. Previous work has demonstrated that the increase in thymus weight with the removal of GCs is probably due to a failure of thymocyte negative selection (27). It has been previously reported that removal of CORT (via ADX) or blockade of GCrs (via RU486) results in a failure to negatively select double-positive (CD4+CD8+) thymocytes (28, 29). This is believed to occur because endogenous CORT produced by both adrenal cortical cells and thymic endothelial cells (30) triggers apoptosis in thymocytes that do not receive a positive selection signal. Thus, the basal CORT replacement in the drinking water plus the thymically produced CORT (30) were sufficient to deliver the necessary apoptotic signal, but insufficient to completely restore anti-KLH IgM production.
Specific mechanisms for the role of the CORT rise 5–7 days after
immunization on the IgG response also remain unclear; however, the
current studies suggest that the CORT rise 5–7 days after immunization
may be important for mediating the IgM to IgG2a switch and optimal
production of IFN-. The effect of GCs on IFN- has been studied in
vitro. The majority of these results would suggest that GCs suppress
IFN- (31). Yet, the data reported here support an
important stimulatory role of low dose endogenous GCs in Ag-specific
IFN- production, such that GCr blockade reduced Ag-specific IFN-
production. There are many possible ways that GCs in vivo could
potentiate anti-KLH Th1 production of IFN-. One reasonable
hypothesis is that the endogenous increase in CORT 5–7 days after KLH
is suppressing some factor that tonically inhibits IFN- production.
One such factor could be NO. NO is very sensitive to GC suppression
(32). In fact, we have found that 1–10 nM CORT in vitro
suppresses NO production (-40%), and that in vivo administration of
RU486 increases NO production by Con A-stimulated splenocytes (+43%;
unpublished observations). In addition, NO has been reported to
selectively suppress Th1 cytokines, such as IL-2 and IFN-
(33). Thus, it is possible that the temporary elevation in
CORT 5–7 days after KLH inhibits NO and releases anti-KLH Th1
cells from NO inhibition. This would result in optimal production of
IFN- from anti-KLH Th1 cells to stimulate the IgM to IgG2a
switch.
Finally, it is important to note that the present data indicate that endogenous GCs participate in the regulation of in vivo Ab formation, and not that they are stimulatory or suppressive in any simplistic sense. Even though removal of endogenous GCs interfered with production of Ab, it should not be inferred that artificial elevation of GCs above the normal levels attained during the immune response would then further increase Ab formation. In fact, Fleshner et al. (16) clearly demonstrated that stress levels of CORT at the time of immunization were without effect on the anti-KLH Ig response.
In contrast to the effects of CORT, DEX greatly suppressed anti-KLH
Ig (Fig. 6). These results clearly highlight the difference between the
impact of synthetic (i.e., DEX) nonphysiological levels and endogenous
physiological levels of GCs. This result could be explained because the
actions of DEX and endogenous GCs are quite different from each other.
DEX does not bind to the corticosteroid-binding globulin
(6). Consequently, equal doses of DEX and CORT do not
result in equal concentrations of unbound or biologically active
steroid. In addition, DEX has a much longer half-life (7).
DEX also has a greater affinity for the type II GCr and a lower
affinity for the type I receptor than do endogenous GCs
(8). Thus, DEX differs in many important ways from
endogenous GCs and bypasses a number of physiological buffering
mechanisms that limit the impact of endogenous GCs on target tissues.
Therefore, it is clearly inappropriate to assume that the effect of DEX
on immune function is reflective of the effects of endogenous
GCs.
In conclusion, the present results encourage further exploration of a physiological and adaptive role for endogenous GCs in mediating humoral immunity and call into the question the simplistic conclusion that GCs are immunosuppressive.
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Footnotes |
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2 Abbreviations used in this paper: GC, glucocorticoid; GCr, GC receptor; ADX, adrenalectomy; CORT, corticosterone; KLH, keyhole limpet hemocyanin; ETOH, ethyl alcohol; DEX, dexamethasone.
Received for publication August 9, 2000. Accepted for publication January 4, 2001.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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 J. D. Johnson, J. Campisi, C. M. Sharkey, S. L. Kennedy, M. Nickerson, and M. Fleshner Adrenergic receptors mediate stress-induced elevations in extracellular Hsp72 J Appl Physiol, November 1, 2005; 99(5): 1789 - 1795. [Abstract] [Full Text] [PDF]
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