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* Departments of Pathology and
Microbiology, University of Virginia, Charlottesville, VA 22908
| Abstract |
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, but not NK1.1+TCRV
+, cells. Ab depletion of NK1.1+TCRV
cells inhibited neonatal AOD development. Moreover, in adoptive transfer of neonatal AOD, recipient disease was ameliorated when either donor or recipient NK cells were depleted. Thus, NK cells operate in both induction and effector phases of the disease. IFN-
was produced by neonatal NK cells in vivo, and it may be important in neonatal AOD. Indeed, ovaries with neonatal AOD expressed high levels of IFN-
and TNF-
which correlated with disease severity, and the disease was inhibited by IFN-
or TNF-
Ab. Importantly, disease was enhanced by recombinant IFN-
, and treatment of T cell donors with IFN-
Ab also significantly reduced adoptive transfer of neonatal AOD. Finally, neonatal AOD was ameliorated in mice deficient in Fc
RIII and was enhanced in Fc
RIIB-deficient mice. We conclude that neonatal NK cells promote pathogenic T cell response at multiple stages during neonatal autoimmune disease pathogenesis. Also operative in neonatal AOD are other mediators of the innate system, including proinflammatory cytokines and Fc
RIII signaling. | Introduction |
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The neonatal AOD model was discovered in the course of a study of adult AOD induced by immunization with an oocyte-specific zona pellucida 3 (ZP3) peptide (ZP3330342) in CFA (9). Adult AOD is dependent on pathogenic autoreactive T cells. To study the role of autoantibodies in AOD, a chimeric peptide, CP2, that contained a foreign T cell epitope and the ZP3 B cell autoepitope (aa 335342) was produced (10). Immunization of CP2 in CFA elicited a strong ZP3 Ab response without a concomitant T cell response to ZP3, and the mice were free of AOD (10). Thus, autoantibodies and autoreactive B cell per se are insufficient to induce AOD in adults.
Although adult female mice injected with CP2 did not develop AOD, severe AOD was found in their female progeny 2 wk after birth (8). Neonatal AOD, triggered by maternal ZP3 autoantibodies transferred in milk, was dependent on the B cell epitope specificity of the autoantibodies, the MHC haplotype, and functional Fc
R. Strikingly, neonatal AOD occurrence also requires the presence of T cells in neonates. Therefore, ZP3 immune complex can trigger activation of autoreactive T cells, probably via Fc
R-positive APC. In parallel to the neonatal AOD study, Greeley et al. (11) reported that T cell-dependent diabetes in NOD mice is significantly ameliorated by prevention of transfer of maternal autoantibodies to both female and male progeny. These findings have prompted the hypothesis that neonatal autoimmunity induced by maternal Ab, which results in progressive and destructive disease, such as diabetes in NOD mice and the congenital heart block in the setting of lupus Abs to Ro and La, may include de novo autoreactive T cell activation.
One of the most intriguing observations about neonatal AOD is that the disease occurred only when ZP3 Ab-positive milk feeding was initiated during the first 5 days of life. This neonatal time window did not appear to depend on neonatal deficiency of CD4+CD25+ regulatory T cells because the infusion of adult CD4+CD25+ T cells failed to protect neonates from neonatal AOD. We considered it more likely that the neonatal innate system may favor the promotion of a T cell response, but may resist CD4+CD25+ T cell regulation. However, our current understanding of the neonatal innate system, including NK cell function, is limited.
In this study we examined the role of neonatal NK cells in the pathogenesis of neonatal AOD. Neonatal NK cells with the capacity to produce IFN-
were found to constitute a significant fraction of neonatal spleen cells. In the presence of immune complex and Fc
RIII, neonatal NK cells were found to promote the induction and effector function of pathogenic T cells, possibly through production of proinflammatory cytokines. This study has therefore demonstrated for the first time a pathogenic role of neonatal NK cells in autoimmune disease pathogenesis.
| Materials and Methods |
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C57BL/6 (B6), A/J, and (C57BL/6 x A/J)F1 (B6AF1) mice were obtained from the National Cancer Institute (Frederick, MD). FcR
subunit and Fc
RIIB-deficient B6 mice were purchased from Taconic Farms (Germantown, NY), and Fc
RIII-deficient B6 mice were obtained from The Jackson laboratory (Bar Harbor, ME). The mice were housed in a specific pathogen-free facility under the animal care and use committee guidelines of University of Virginia.
To generate autoantibodies to native antigenic epitopes of mouse ZP3, we used a chimeric peptide named CP2 (NCAYKTTQANKQAQIHGPR) that contained a bovine RNase T cell epitope 94104 (underlined) linked to the modified native self B cell epitopes of ZP3335342 (QFQIHGPR), in which Phe336, a critical residue of the T cell epitope, was replaced by an alanine. The peptide was synthesized by Multiple Peptide Systems (San Diego, CA) with >90% purity as determined by HPLC.
IFN-
-neutralizing mAb (clone XMG1.2) and TNF-
-neutralizing mAb (clone MP6-XT3) and Abs used for IFN-
detection in the ELISA were obtained from BD Pharmingen (San Diego, CA). Recombinant mouse IFN-
and IL-12 were obtained from BD Pharmingen and R&D Systems (Minneapolis, MN), respectively. For NK cell depletion, PK136 mAb (BD Pharmingen) against NK1.1 Ag and rabbit polyclonal Abs against asialo-GM1 (AGM1) (Cedarlane Laboratories, Hornby, Canada) were used.
Immunization and neonatal AOD induction by milk feeding or serum transfer
Immunization was performed as described previously (8). In short, 6- to 8-wk-old B6 or B6AF1 mice were injected with 50 nmol of CP2 in CFA in one footpad and at the base of the tail. One month after immunization, the ZP3 Ab titer was determined by indirect immunofluorescence staining of a frozen ovarian section.
For neonatal AOD induction by milk feeding, CP2-immunized B6 female mice were impregnated by normal A/J males. The neonatal AOD was constantly observed when the fluorescence serum ZP3 autoantibodies titers of milk donors exceeded 1/1000. In some cases, naive B6AF1 pups were fostered to the ZP3 autoantibody-positive postpartal dams starting from day 3 of age. For neonatal AOD induction by serum transfer, sera with a fluorescence ZP3 autoantibody titer at or exceeding 1/3000 were pooled from CP2-immunized male or female mice, and 100 µl of serum was injected i.p. into naive neonatal B6AF1 mice on days 3 and 5. All ZP3 autoantibodies recipients were euthanized at 14 days of age.
Histopathologic grading of neonatal AOD
Mouse ovaries were fixed in Bouins fixative and embedded in paraffin, and 5-µm-thick sections were stained with H&E. The severity index of neonatal AOD was determined without knowledge of the identity of the mice under study. A severity grade of one to four was assigned to each of the following histopathologic changes: 1) oophoritis or ovarian inflammation, 2) depletion of growing oocytes, and 3) depletion of primordial oocytes. An oophoritis grade of 1 denotes one or two foci of leukocyte infiltration, grades 23 represents an incremental numbers of multifocal inflammatory foci; and grade 4 is diffuse inflammation. Loss of each type of oocytes was graded 1 when occasional oocytes were lost from the follicle and were graded 4 when all oocytes disappeared. Grades 2 and 3 represent partial and incremental oocyte loss between grades 1 and 4. Because the loss of oocytes results in a reduction of ovarian function, their grades were weighed as follows: the grade for growing oocyte loss was multiplied by 1.5, and those of primordial oocyte loss were multiplied by 2. Accordingly, the total disease severity index was calculated as: oophoritis grade + (growing oocyte loss grade x 1.5) + (primordial oocyte loss grade x 2.0). and the total neonatal AOD scores ranged from 1 to 18.
T cell enrichment and transfer, in vivo cytokine neutralization, and NK cell depletion
For adoptive transfer, T cells were enriched from the spleens of 2-wk-old ZP3 Ab recipients using T cell enrichment column (R&D Systems, Minneapolis, MN). T cells with purity of >90% were injected i.p. into 3-day-old normal B6AF1 pups at 2 x 106 cells/mouse. The cell recipients were studied 11 days after cell transfer.
To neutralize cytokine and deplete NK cell in vivo, the appropriate mAb was injected i.p. at 20 µg/injection every 3 days starting on day 3. A 50- to 100-µl volume of Ab was injected through a 30-gauge needle inserted s.c. from the chest to the level of the abdomen and then into the peritoneal cavity. After injection, the needle was withdrawn very slowly to avoid leakage of Ab. All mice were studied at 14 days of age.
To verify depletion of NK cell function, NK cell-depleting Ab was injected i.p. at 20 µg/pup into 5-day-old pups. Two days later, the pups were injected i.p. with LPS at 20 µg/pup, and sera were collected 6 h later. Serum IFN-
levels were measured by ELISA.
Flow cytometric analysis
Single-cell suspensions were prepared from the spleen or lymph nodes. Contaminating RBC were lysed using ACK lysing buffer (BioSource International, Camarillo, CA). After two washes, Fc
RIIB/III were blocked by incubation with 2.4G2 Ab at 4°C for 20 min. The cells were incubated for 20 min on ice with the desired fluorochrome-conjugated mAbs or isotype control Ig at 0.5 µg/106 cells. The cells were washed twice with PBS/1% BSA, fixed in 2% paraformaldehyde, and analyzed by FACScan (BD Biosciences, San Jose, CA) using the CellQuest program (BD Biosciences).
RNA extraction and real-time PCR
Quantitative real-time RT-PCR was performed using a sequence detector (model 7700; Applied Biosystems, Foster City, CA). Total RNA from one ovary of each mouse receiving ZP3 autoantibodies or control Ab was extracted using the RNeasy minikit (Qiagen, Valencia, CA). The cDNA was then generated with 1 µg of total RNA using the TaqMan RT kit (Applied Biosystems). Briefly, total RNA was added to 50 µl of RT reaction mixture (1x RT buffer, 5.5 mM MgCl2, 500 µM dNTP, 2.5 µM random hexamers, 0.4 U/µl RNasin (RNase inhibitor), and 1.25 U/µl Multiscribe reverse transcriptase) at 25°C for 10 min, 48°C for 30 min, and finally 98°C for 5 min to inactivate reverse transcriptase. Real-time PCR were performed using TaqMan Pre-Developed Assay reagents for cytokine gene expression kits (Applied Biosystems) according to the manufacturers instructions. The results were analyzed using SDS software (Applied Biosystems). The final data were normalized to the expression of GADPH, a housekeeping gene.
Statistical analyses
Statistical differences were determined by nonparametric Wilcoxon test or nonparametric Mann-Whitney test. Significance was considered at p
0.05 in all experiments.
| Results |
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The spleens of 3- or 9-day-old mice contained a significant number of NK1.1+ cells that did not express TCRV
(Fig. 1A). In contrast, very few, if any, NKT cells (NK1.1+TCRV
+ cells) were detectable in the neonatal spleen. The average ratio of NK cell to 
TCR+ T cells in the 3-day-old mice was 0.6, and it declined to 0.2 by day 9 as T cell numbers increased.
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level reached 30.5 ± 6.3 ng/ml. To demonstrate that NK cells were a source of the serum IFN-
, the mice were treated with anti-NK1.1 Ab or anti-AGM1 Ab before LPS injection, and as shown in Fig. 1B, serum IFN-
levels were reduced to 9.6 ± 2.4 and 1.6 ± 0.4 ng/ml, respectively. The AGM1 Ab was found to be more efficient in depleting neonatal NK cells (CD3DX5+ cells) than the NK1.1 Ab (60% reduction (n = 8) vs 49% (n = 9); Fig. 1C); this may account for the difference in serum IFN-
reduction of the two treatment groups (Fig. 1B). Altogether, neonatal NK cells are well represented in neonatal mice, and they produce IFN-
in response to LPS in vivo. We next determined the effect of NK cell depletion on the development of neonatal AOD induced by ZP3 autoantibodies. The incidence of neonatal AOD was 27% (three of 11 mice) in the recipients of ZP3 autoantibody-positive milk after NK cell depletion by NK1.1 Ab; this was significantly less than the disease incidence of 80% in control mice (Fig. 2A). The effect of rabbit Ab to AGM1 was even more dramatic. None of the mice with NK cell depletion developed neonatal AOD, whereas 100% of the control mice developed severe neonatal AOD (Fig. 2B). The possibility that the effect was due to NKT cell depletion is unlikely because NKT cells are not depleted by AGM1 Ab treatment (Fig. 1C) (12, 13, 14).
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Neonatal NK cells may participate in the induction phase of neonatal AOD by responding to ZP3 Ag-Ab complexes and, through cytokines, activate DC and promote a T cell response. Alternatively, they may cooperate with effector T cells downstream by facilitating tissue inflammation and/or cytolysis. To dissect these possibilities, we studied the effect of neonatal NK cell depletion on the adoptive transfer of neonatal AOD. As shown in Fig. 3, the spleen T cells from mice with neonatal AOD adoptively transferred severe ovarian inflammation to normal syngeneic pups. To investigate neonatal NK cell requirement in the effector phase of neonatal AOD, NK cells were depleted from the T cell recipients by AGM1 Ab. As shown in Fig. 3A, this treatment reduced the disease incidence in T cell recipients from 62% (eight of 13) to 29% (four of 14; p = 0.016). Thus, the neonatal NK cells participate in promoting inflammation triggered by autoreactive T cells manifested in the cell recipients that are devoid of immune complexes.
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Therefore, neonatal NK cells participate in multiple stages of neonatal AOD pathogenesis. They assist in the induction of the effector T cell response as well as in the functional expression of activated effector T cells.
Severity of neonatal AOD correlates with ovarian expression of IFN-
and TNF-
To investigate other mechanisms of innate immunity that may also require neonatal NK cell action, we studied the influence of proinflammatory cytokines, including IFN-
and TNF-
, on neonatal AOD development. mRNA isolated from the ovaries of mice that received ZP3 autoantibody-positive milk and the control mice were studied for the expression of these cytokines by real-time RT-PCR. Significantly higher levels of IFN-
and TNF-
mRNA were detected in the ovaries of ZP3 autoantibody recipients than in control ovaries (Fig. 4A). The experimental to control ratio was 11.0 for IFN-
and 4.4 for TNF-
. When the cytokine mRNA levels of individual mice were analyzed against ovarian disease severity, a highly significant correlation was found for both cytokines (Fig. 4, B and C).
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or TNF-
and was promoted by rIFN-
or IL-12
We next documented the pathogenic role of IFN-
and TNF-
in neonatal AOD by treatment with neutralizing Ab to the cytokines. As shown in Fig. 5A, mild neonatal AOD developed in two of nine (22%) ZP3 Ab recipients treated with IFN-
Ab and in three of 11 (27%) mice treated with TNF-
Ab. In contrast, severe neonatal AOD developed in 17 of 18 (94%) recipients of ZP3 Ab-positive milk and control rat IgG.
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, all 12 neonatal mice developed very severe neonatal AOD with complete ovarian atrophy. Similar results were obtained when the mice were coinjected with recombinant murine IL-12, a cytokine known to activate NK cells (Fig. 5B).
Therefore, the proinflammatory cytokines, including IFN-
, TNF-
, and IL-12, are clearly operative in the pathogenesis of neonatal AOD. However, this study did not clarify whether NK cells were the source of the pathogenic cytokines.
Role of IFN-
in the induction phase of neonatal AOD
Activated NK cells and Th1 cells are principal producers of IFN-
in an immune response. To address the role of IFN-
production by NK cells in neonatal AOD, we studied the requirement for IFN-
during the induction phase of pathogenic T cells. IFN-
was neutralized in T cell donors before disease transfer. As shown in Fig. 5C, only one of nine mice that received T cells from IFN-
Ab-treated cell donors developed AOD, whereas five of seven recipients of T cells from mice treated with control Ab developed AOD (p = 0.011). Therefore, neonatal AOD was inhibited when IFN-
was neutralized only during the inductive phase of the disease.
Neonatal AOD induction is dependent on Fc
RIII
IFN-
has been reported to promote stimulatory Fc
R functions by decreasing the expression of inhibitory Fc
RIIB and increasing the expression of stimulatory Fc
RIIA on human monocytes (15). In the recent study we evaluate the roles of stimulatory and inhibitory Fc
R in neonatal AOD. Our previous study has indicated that Fc
R-positive cells are critical for neonatal AOD induction (8), and the inhibiting effect of 2.4G2 mAb was confirmed in the present study (Fig. 6A). Although this mAb can block the inhibitory Fc
RIIB and the stimulatory Fc
RIII, NK cells are known to express predominantly Fc
RIII, not Fc
RIIB (16). To examine the role of Fc
RIII further, we compared the contributions of Fc
RIIB vs Fc
RIII by studying neonatal AOD in wild-type C57BL/6 (B6) mice and B6 mice deficient in the FcR common
-chain, only Fc
RIII, or only Fc
RIIB.
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and Fc
RIII. Thus, two of 26 (8%) B6 mice deficient in FcR
and none of the 14 B6 mice deficient in Fc
RIII developed neonatal AOD. In contrast, the disease incidence and severity in B6 mice deficient in Fc
RIIB were higher than those in wild-type B6 pups (p = 0.041). We conclude that Fc
RIII is required to promote neonatal AOD, whereas engagement of Fc
RIIB has the opposite effect. | Discussion |
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R. However, the occurrence of neonatal AOD also required de novo activation of pathogenic CD4+ T cells, presumably by the tissue immune complexes. Thus, neonatal mice rendered T cell deficient were resistant to disease, whereas the CD4+ T cells from mice with neonatal AOD were able to adoptively transfer severe disease to naive neonatal recipients. We have since found that neonatal AOD development depends on T cell costimulation and requires Th1 cytokines (E. T. Samy, Y. Setiady, and K. Tung, unpublished observations). An intriguing finding in neonatal AOD was the requirement for ZP3 Ab to reach the neonate within the first 5 days of life. To investigate this neonatal time window, we found that depletion of CD4+CD25+ T cells would allow the pups that received the ZP3 Ab beyond the neonatal window (after 9 days of age) to develop disease; however, the disease was not preventable by infusion of adult CD4+CD25+ T cells. It was postulated that the neonatal environment may be resistant to the CD4+CD25+ T cell action. For example, innate immune cells, including NK cells, macrophages, and DC, are known to influence the adaptive immune response as well as to inhibit the regulatory function of CD4+CD25+ T cells (17). Therefore, in this study we investigated the neonatal innate system, specifically the role of NK cells in neonatal AOD.
NK cells were readily detected in 3-day-old spleens using NK1.1 Ab in numbers that surpass those of NKT cells but approximate those of T cells. The finding is consistent with the report by Ortaldo et al. (18). After day 3, the relative number of NK cells in the spleen declined as T cell numbers increased. Neonatal NK cells produce similar amounts of IFN-
as adult NK cells in response to LPS stimulation (19). Most importantly, neonatal NK cells were documented to be required for the pathogenesis of neonatal AOD. When they were depleted from the neonatal mice by NK1.1 or AGM1 Ab, disease development was completely inhibited. This provides the first demonstration that murine neonatal NK cells are functional and that they support the development of T cell-mediated autoimmune disease.
Because neonatal AOD has complex mechanisms, involving initially immune complex and subsequently the CD4+ T cell response, the activated NK cells may participate in different stages of disease when the immune complex may or may not be present. To differentiate between these alternatives, we studied NK cells in the adoptive transfer of neonatal AOD, when the immune complexes would be present in the cell donors, but not in the T cell recipients. Our results clearly showed that the recipient disease was ameliorated regardless of whether the NK cells were removed from the T cell donors or the T cell recipients. Therefore, NK cells are involved in both the inductive phase and the effector phase of neonatal AOD.
Previous studies of the role of NK cells in adult autoimmune disease have reported somewhat controversial results (reviewed in Ref. 20). Reports of disease amelioration upon NK cell depletion (21, 22, 23, 24, 25, 26) were not confirmed in other studies (27, 28, 29, 30, 31, 32). However, the research was based on several disease models that required different methods of induction, and they may have different pathogenetic mechanisms. An exception is EAE in C57BL/6 mice immunized with the myelin oligodendrocyte gp3555 peptide in adjuvant. Zhang et al. (27) immunized the mice shortly after NK cell depletion with Ab and found disease enhancement, whereas Shi et al. (21) depleted NK cells with Ab 2 days before immunization and reported disease reduction. Besides the timing of NK cell depletion, the studies were conducted in different laboratories and may have been influenced by different environmental factors that can impact autoimmune disease development (33).
Comparison of adult NK cells in adult autoimmunity with neonatal NK cells in neonatal autoimmunity would also be misleading because many differences exist between neonatal and adult NK cells. For example, the cytolytic activity of purified neonatal NK cells against the classical NK cell targets was barely detectable until the mice reached 23 wk of age (34, 35). Jamieson et al. (36) documented that progenitors of neonatal NK cells underwent more rapid division than adult cells. The expression of receptors for MHC class I or class I-like molecule of the Ly49 and CD94/NKG2 families on adult NK cells was also far more diverse than that detected on neonatal NK cells. In particular, neonatal NK cells were reported to express predominantly CD94/NKG2A (37, 38), and the Ly49 receptors were not detectable until after 1 wk (18). It has even been suggested that NK cells from adult vs neonates may differ in their capacity of self/nonself discrimination.
NK cells may affect neonatal AOD by modifying the APC function of DC. Indeed, NK cells have recently been shown in vitro to induce DC maturation and cytokine production, and these events can, in turn, enhance T cell activation (39, 40, 41, 42, 43). Interaction of NK cells and DC can be bidirectional; and activated DC have been shown to induce proliferation, activation, and cytokine production by NK cells (39, 40, 41, 44, 45). The two cells may communicate by cell contact or via proinflammatory cytokines such as IFN-
and TNF-
(39, 40, 41, 44). In this context, it is of interest that the same cytokines are found in the present study to strongly influence neonatal AOD pathogenesis. When IFN-
was blocked, neonatal AOD development was abrogated, and the capacity to adoptively transfer disease by CD4+ T cells was inhibited. The latter finding, which indicated that IFN-
is involved during the process of T cell induction, provides strong support for the NK cell as the source of the proinflammatory cytokines.
Our study has shown that a balance between stimulatory and inhibitory Fc
R is critical in neonatal AOD; Fc
RIII engagement promotes neonatal AOD, whereas Fc
RIIB engagement has the opposite effect. These two Fc
Rs share similar specificities, but have opposite functions in promoting inflammation; Fc
RIII is proinflammatory, whereas Fc
RIIB opposes the stimulatory signals (46). Because the immune complex is responsible for triggering neonatal AOD, it may engage the Fc
R on NK cells, DC, or both. Because NK cells express predominantly Fc
RIII, this may explain the dominant effect of Fc
RIII deficiency on neonatal AOD development. In contrast, both Fc
RIIB and Fc
RIII are expressed on DC, and they could modulate the outcome of T cell activation in response to the DC that process the immune complexes. The finding that Fc
RIIB-deficient DC exhibit a lower threshold of activation by immune complex could explain the enhanced severity of neonatal AOD in Fc
RIIB-deficient mice (2). Finally, Fc
R is widely expressed in granulocytes, monocytes, and macrophages and with the attachment of cytophilic Ab to these cells, they may also contribute to neonatal AOD development.
Although our study investigated neonatal NK cells in an autoimmune response, the results could have broader implications and are applicable to in vivo investigation of the neonatal immune response in general. Many studies that compared neonatal and adult mice using in vitro approaches have described deficiency or immaturity in neonatal T cell and neonatal APC function (47, 48, 49, 50). In contrast, many in vivo studies of T and B cell responses to Ag with adjuvant or viral infections have reported comparable responses in neonatal and adult mice (51, 52, 53). Perhaps some of the discrepancies between the in vitro and in vivo findings would be reconciled if the participation of neonatal NK cells is included in the equation. As neonatal NK cells are now documented to have an important role in promoting neonatal autoimmunity, they are likely to also enhance neonatal APC function in other types of immune responses. Our study, therefore, emphasizes the importance of incorporating the interaction of innate and adaptive immunities in research on the ontogeny of immune response.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Yulius Y. Setiady, Department of Pathology, P.O. Box 800214, University of Virginia, Charlottesville, VA 22908. E-mail address: js5bk{at}virginia.edu ![]()
3 Abbreviations used in this paper: DC, dendritic cell; AGM1, asialo-GM1; AOD, autoimmune ovarian disease; CP2, chimeric peptide 2; ZP3, zona pellucida 3. ![]()
Received for publication February 26, 2004. Accepted for publication May 14, 2004.
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