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CUTTING EDGE |


* Center for Neurologic Diseases, Brigham and Womens Hospital, Boston, MA 02115;
Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, and Department of Neurology, Harvard Medical School, Boston, MA 02115; and
Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305
| Abstract |
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, IL-6, and IL-17. Male CD4+CD25 effector cells depleted of Treg cells proliferate to a greater degree than those from females in response to either anti-CD3 or PLP 139151. These data suggest that because of their capacity to regulate potent autoaggressive effector cells, Treg cells partly contribute to the resistance to autoimmunity in the male mice. | Introduction |
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A subset of CD4+ cells called CD4+CD25+ regulatory T (Treg) cells that expresses Forkhead box P3 (Fox P3) can control autoimmune responses (8, 9, 10). Estrogen modulates the expression of Fox P3 mRNA and middle-aged male mice with EAE have diminished Treg cell activity (11, 12), but it is not known whether Treg cell functions are affected by gender.
Immunization with myelin proteolipid protein (PLP) 139151 results in EAE in male and female SJL (I-As) mice with comparable severity, but only female mice show chronic relapsing-remitting disease (13, 14). In contrast, B10.S mice (H-25 congenic with SJL) are relatively resistant to PLP 139151-induced EAE (15), but it is not known whether gender affects resistance. Using IAs tetramers for PLP 139151, we found more myelin PLP-specific Treg cells in the naive periphery of female B10.S mice than in SJL mice (15). Depletion of Treg cells in vivo in female B10.S mice predisposed them moderately to EAE.
We report here that although male B10.S mice have fewer PLP 139151 tetramer+ CD4 cells than female mice, depletion of Treg cells in vivo makes them more susceptible to PLP 139151-induced EAE with increased inflammatory cytokine production and more severe clinical and histological disease than nondepleted mice. Although male and female B10.S mice have comparable Treg cell functions, effector cells expand more in male than in female mice in response to TCR-mediated stimulation. These results indicate that Treg cells partly contribute to gender differences in EAE susceptibility.
| Materials and Methods |
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B10.S (B10.S-H2s/Sg) wild-type (wt) mice 48 wk old were obtained from McLaughlin Research Institute. B10.S/Sg-Tg(TcrPLP)1858Hpw mice (referred to as 5B6 transgenic (tg) B10.S mice) transgenic for the PLP139151-specific TCR 5B6 were generated and maintained as described previously (16).
Peptide synthesis and immunization procedures
PLP 139151 (HSLGKWLGHPDKF) and neuraminidase (NASE) 101120 (EALVRQGLAKVAYVYKPNNT) were synthesized on Fmoc chemistry and used for immunizations as described previously (15).
Proliferation assays
To assess inhibitory effects of Treg cells, PLP 139151-specific 5B6 tg T cells were fractionated into CD4+CD25+ and CD4+CD25 cells by magnetic separation (Miltenyi Biotec). They were plated at a density of 1 x 106 cells/ml in the presence of APCs and PLP 139151 (20 µg/ml) for 2 days in complete DMEM. After pulsing with 1 mCi of [3H]thymidine (1 Ci = 37 GBq) for 16 h, proliferation was measured as counts per minute. CD3+ T cells enriched by negative selection (R&D Systems) from immunized B10.S wt mice were stimulated with PLP 139151 in the presence of APCs. Response of CD4+CD25 T cells to anti-CD3 (1 µg/ml, clone, 145-2C11; BD Pharmingen) was tested with CD11c+ cells as APCs.
Flow cytometry
To study cellular subsets in lymph nodes, various mAbs procured from BD Pharmingen. After staining, cells were analyzed by flow cytometry (FACSCalibur; BD Biosciences); data were analyzed using FlowJo software (Tree Star).
IAs tetramer staining
Frequencies of Ag-specific T cells were determined by flow cytometry using IAs/PLP 139151 and Theilers murine encephalomyelitis virus (TMEV) 7086 tetramers (negative control) as described previously (15). Four-color analysis included anti-CD25/FITC (clone, 7D4), IAs tetramers (PE), 7-aminoactinomycin D (7-AAD), and anti-CD4-allophycocyanin (clone, RM4-5). Percentages of tetramer+ cells in the live (7-AAD) CD4+ population were determined.
Cytokine analysis
CD3+ T cells were enriched from anti-CD25- and control Ig-treated B10.S mice 10 days after immunization with PLP 139151. They were stimulated with APCs loaded with PLP 139151 (50 µg/ml) for 46 days. Supernatants on day 2 were tested for cytokines by ELISAs, and frequencies of cytokine-secreting cells were determined on day 4 by intracellular staining, as described previously (15).
Real-time (TaqMan) RT-PCR
Total RNA was extracted from CD4+CD25 and CD4+CD25+ cells from a group of B10.S mice followed by treatment with DNase 1 (RNeasy kit; Qiagen). cDNA was synthesized using TaqMan RT reagents (Applied Biosystems). Fox P3 and GAPDH mRNA was measured by PCR in separate tubes in duplicates using probes labeled with FAM and VIC and with TAMRA as a quencher using TaqMan universal mix and the ABI Prism 7700 sequence detection system (Applied Biosystems). Primers and probe for GAPDH were purchased (Applied Biosystems). Fox P3 sequences were as described previously (17). A comparative threshold cycle (CT) was used to determine mRNA expression of Fox P3 and GAPDH relative to no-template control (calibrator). CT value was normalized for each sample using the formula:
CT = CT (Fox P3) CT (GAPDH), and the relative expression of Fox P3 was then calculated using the formula 2CT.
Histopathology
Following induction of EAE, the mice were monitored for clinical signs of disease for 4 wk and scored as described previously (13). Mice were killed when their score reached
4 or when they began to recover. Brains and spinal cords were fixed in 10% phosphate-buffered formalin. Histologic disease was evaluated as previously described (13) and polymorphonuclear leukocyte (PMN) infiltration as described in Table I legend.
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Students t test was used to determine significance of data except for rank correlations between inflammatory foci and PMN scores, which were determined by Wilcoxon signed rank test. A value of p
0.05 was considered significant.
| Results and Discussion |
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-producing cells and induction of EAE in
30% of mice (15). Because autoimmune diseases are more common in females than males, we hypothesized that there may be gender differences in the function of the naturally occurring CD4+CD25+ Treg cell subset.
When we depleted Treg cells in vivo by administration of anti-CD25 Ab in male B10.S mice before immunization, 85% of the mice (12 of 14) developed moderate to severe EAE, whereas only 3 of 12 control mice (25%) developed mild EAE, i.e., loss of tail tonicity (p
0.001) (Table I). In agreement with our previous results (15), a small number of female B10.S mice (three of nine, 33%) depleted of Treg cells but no control Ab-treated mice developed disease, suggesting that genetic resistance to EAE in female B10.S mice does not lie entirely in the Treg population. In female B10.S mice, multiple factors may contribute to EAE resistance, i.e., Ag-specific defects in Th1 cytokine secretion and IL12-Rb2 expression (18, 19), a tendency to produce elevated amounts of Th2 cytokines (20), APCs (16) and the presence of a high proportion of Treg cells that react with PLP 139151 tetramers in their naive periphery (15). Once males develop EAE following anti-CD25 treatment, there were no other clinical differences between males and females. Histologic disease in anti-CD25 Ab-treated male mice was significantly greater than in the controls (p
0.0003) (Table I), and there were more PMNs in CNS infiltrates (p
0.0004) (Table I, Fig. 1). The histologic disease in males was also more severe than in anti-CD25-treated females (mean total inflammatory foci = 124.9 vs 44.8) (p
0.05). The disease severity in females was enhanced when compared with control mice but inflammatory foci contained fewer neutrophils (Table I, Fig. 1b).
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We first determined that male B10.S mice have a higher percentage of CD3+ cells in their lymph nodes than age-matched female B10.S mice, but the percentage of Treg cells is lower in males (Table II). We then confirmed that Treg cells in male and female B10.S mice are equally effective in inhibiting expansion of effector cells using anti-CD3 as a stimulus (data not shown). FoxP3 mRNA, a marker for Treg cells, was also expressed in comparable amounts (Fig. 2a). Therefore, we could identify no major differences in Treg populations between male and female B10S mice. We next tested whether Treg cells from male and female B10.S mice have any defect in their suppressive function in response to self-Ags using TCR tg mice specific to PLP 139151 (16). We found that Treg cells from male and female tg B10.S mice did not proliferate to PLP 139151, whereas male and female effector cells responded equally well to PLP 139151. Treg cells inhibited the proliferative response of effector cells but there were differences; the inhibition of CD4+CD25 cells mediated by Treg cells in female B10.S mice was maintained even at low ratios of regulatory:effector cells. However, in male mice as ratios of Treg cells to effectors were lowered, the effector cells expanded to a greater extent (Fig. 2b). This suggests either that Treg cells from female mice are more efficient in their suppressive function than those in males or that the effector cells in males are capable of responding to autoantigens more vigorously than those in females. We quantified the precursor frequency of PLP 139151 tetramer+ cells in male mice to be 0.04% of CD4 cells (8 in 20,000). By contrast, the precursor frequency in female B10.S mice is 40 in 20,000 CD4 cells (15). We did not observe any significant shift in PLP 139151 tetramer reactivity in effector vs Treg cells, as previously reported in female B10.S mice (15) (data not shown). Therefore, the higher incidence and greater severity of EAE in male B10.S mice are unlikely to be due to an increased frequency or function of PLP 139151-specific Treg cells.
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3-fold more in the anti-CD25 Ab-treated males compared with controls (Fig. 3b). This response was specific because there was negligible reactivity to TMEV 7086 tetramers. These data suggest that the expansion of PLP 139151-reactive cells in mice depleted of Treg cells contributed to the more severe disease. This expansion appeared to have resulted from the loss of regulation mediated by Treg cells, which can prevent the expansion of effector cells in an Ag nonspecific manner (21).
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(2, 22). We tested whether a similar bias exists in immunized male B10.S mice, with or without Treg cell depletion. By ELISA, the production of both IL-2 (p
0.01) and IFN-
(p
0.006) was significantly elevated, with a marginal increase in IL-17 production (p
0.08) on day 2 in the cultures derived from CD25+ cell-depleted male mice compared with controls (Fig. 3c). As previously noted in female B10.S mice (15), IL-10 secretion was reduced in the anti-CD25 Ab-treated group (p
0.02), suggesting that Treg cells may directly or indirectly regulate IL-10 production. However, by intracellular staining, the frequencies of cells secreting all of the cytokines tested (IL-2, IL-4, IL-6, IL-10, IL-17, and IFN-
) were elevated in anti-CD25-treated male mice (Fig. 3c). Among proinflammatory cytokines, IFN-
-secreting cells were present at a higher frequency (3.09 vs 1.35) followed by IL-17 (1.09 vs 0.41) and IL-6 (0.5 vs 0.21) in the anti-CD25-treated vs control mice. The number of TNF-
-secreting cells did not vary between groups (data not shown). Recently, it was reported that IL-23-dependent production of inflammatory cytokines (IL-17, IL-17F, IL-6, and TNF-
) is essential for the development of CNS inflammation (23). In anti-CD25 Ab-treated mice, the numbers of cells that secrete IFN-
, IL-6, and IL-17 was increased, implying that Treg cells regulate the expression of these cytokines. In the absence of Treg cells, the effector cells producing inflammatory cytokines may expand resulting in altered chemokines and increased proportions of PMNs in inflammatory foci (24). We then sought to detect any fundamental difference in the expansion of effector cells between male and female B10.S wt mice. Using anti-CD3 as a stimulus, we observed that the effector cells from male B10.S mice expanded to a greater extent than those from female mice (Fig. 4a). To verify that a similar differential response occurs to PLP 139151, we immunized groups of male and female B10.S mice with PLP 139151 after treating them with anti-CD25 or control Ab. We measured the PLP 139151-specific response by [3H]thymidine incorporation. As expected, mice depleted of CD25+ cells responded to PLP 139151 significantly more strongly than controls of either sex (Fig. 4b). However, the T cell response to PLP 139151 in the male B10.S mice tended to be higher than in the female mice treated with anti-CD25 Ab, especially at lower Ag concentrations (Fig. 4b). Similar trends were confirmed by using 5B6 tg T cells specific to PLP 139151 (data not shown). These data suggest that the autoreactive effector cells in male B10.S mice can respond to autoantigens vigorously, but they are kept in check by Treg cells.
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| Disclosures |
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| Footnotes |
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1 This work is supported by National Institutes of Health Grants R01 NS30843, P01 NS38037, and R01 AI44880, NS 046414 (to R.A.S.), P01 A145757 and R01 NS44914 (to K.W.W.), and National Multiple Sclerosis Society Grant 2571-D9 (to V.K.K.). V.K.K. is the recipient of Javitz Neuroscience Investigator Award. ![]()
2 Address correspondence and reprint requests to Dr. Vijay K. Kuchroo, Center for Neurologic Diseases, Brigham and Womens Hospital, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115. E-mail address: vkuchroo{at}rics.bwh.harvard.edu ![]()
3 Abbreviations used in this paper: EAE, experimental autoimmune encephalomyelitis; Treg, regulatory T; PLP, proteolipid protein; wt, wild type; tg, transgenic; TMEV, Theilers murine encephalomyelitis virus; 7-AAD, 7-aminoactinomycin D; PMN, polymorphonuclear leukocyte. ![]()
Received for publication June 10, 2005. Accepted for publication September 1, 2005.
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