Ly6Chigh monocytes facilitate transport of Murid herpesvirus 68 into inflamed joints of arthritic mice

Viruses, particularly the Epstein‐Barr virus (EBV) has long been suspected to exacerbate acute arthritic symptoms. However, the cell populations that contribute to import viruses into the inflamed tissues remain to be identified. In the present study, we have investigated the role of monocytes in the transport of Murid herpesvirus 68 (MHV‐68), a mouse virus closely related to EBV, using the serum transfer‐induced arthritis (STIA) model. We found compelling evidence that MHV‐68 infection markedly increased disease severity in NR4A1^?/? mice, which are deficient for Ly6C^low monocytes. In contrast, the MHV‐68‐induced enhancement of joint inflammation was lessened in CCR2^?/? mice, suggesting the involvement of inflammatory Ly6C^high monocytes in viral transport. We also observed that following selective depletion of monocyte subsets by administration of clodronate, MHV‐68 transport into the synovium occurs only in the presence of Ly6C^high monocytes. Tracking of adoptively transferred Ly6C^high GFP infected monocytes into arthritic CCR2^?/? mice by two‐photon intravital microscopy showed that this monocyte subset has the capacity to deliver viruses to inflamed AR joints, as confirmed by the detection of viral DNA in inflamed tissues of recipient mice. We thus conclude that Ly6C^high monocytes import MHV‐68 when they are mobilized to the inflamed arthritic joint.     

Detection of vasostatin‐1‐specific CD8+ T cells in non‐obese diabetic mice that contribute to diabetes pathogenesis

Chromogranin A (ChgA) is an antigenic target of pathogenic CD4⁺ T cells in a non‐obese diabetic (NOD) mouse model of type 1 diabetes (T1D). Vasostatin‐1 is a naturally processed fragment of ChgA. We have now identified a novel H2‐K^d‐restricted epitope of vasostatin‐1, ChgA 36‐44, which elicits CD8⁺ T cell responses in NOD mice. By using ChgA 36‐44/K^d tetramers we have determined the frequency of vasostatin‐1‐specific CD8⁺ T cells in pancreatic islets and draining lymph nodes of NOD mice. We also demonstrate that vasostatin‐1‐specific CD4⁺ and CD8⁺ T cells constitute a significant fraction of islet‐infiltrating T cells in diabetic NOD mice. Adoptive transfer of T cells from ChgA 36‐44 peptide‐primed NOD mice into NOD/severe combined immunodeficiency (SCID) mice led to T1D development. These findings indicate that vasostatin‐1‐specific CD8⁺ T cells contribute to the pathogenesis of type 1 diabetes in NOD mice.     

Mast cells control insulitis and increase Treg cells to confer protection against STZ‐induced type 1 diabetes in mice

Quantitative alterations in mast cell numbers in pancreatic lymph nodes (PLNs) have been reported to be associated with type 1 diabetes (T1D) progression, but their potential role during T1D remains unclear. In this study, we evaluated the role of mast cells in T1D induced by multiple low‐dose streptozotocin (MLD‐STZ) treatments, using two strains of mast cell‐deficient mice (W/W^v or Wsh/Wsh) and the adoptive transfer of mast cells. Mast cell deficient mice developed severe insulitis and accelerated hyperglycemia, with 100% of mice becoming diabetic compared to their littermates. In parallel, these diabetic mice had decreased numbers of T regulatory (Treg) cells in the PLNs. Additionally, mast cell deficiency caused a significant reduction in IL‐10, TGF‐β, and IL‐6 expression in the pancreatic tissue. Interestingly, IL‐6‐deficient mice are more susceptible to T1D associated with reduced Treg‐cell numbers in the PLNs, but mast cell transfer from wild‐type mice induced protection to T1D in these mice. Finally, mast cell adoptive transfer prior to MLD‐STZ administration conferred resistance to T1D, promoted increased Treg cells, and decreased IL‐17‐producing T cells in the PLNs. Taken together, our results indicate that mast cells are implicated in resistance to STZ‐induced T1D via an immunological tolerance mechanism mediated by Treg cells.     

miR-196a通过靶向NR6A1降低宫颈癌Hela细胞生存和运动能力

目的探究微小型RNA-196a(miR-196a)对宫颈癌Hela细胞生存和运动能力的影响和作用机制。方法RT-PCR检测正常宫颈上皮HcerEpic细胞和宫颈癌Hela细胞、CaSki细胞中miR-196a和核受体NR6A1的mRNA水平;阴性对照miR-NC和miR-196a inhibitor转染Hela细胞,分别记为NC组和miR-196a inhibitor组,免疫印迹检测NR6A1蛋白的表达,生物信息学和荧光素酶报告实验分析和验证miR-196a和NR6A1的靶向调控关系;阴性对照质粒pcDNA和过表达质粒pcDNA-NR6A1转染Hela细胞,分别记为pcDNA组和pcDNA-NR6A1组,免疫印迹检测NR6A1蛋白表达;将miR-196a inhibitor和pcDNA-NR6A1单独或联合转染Hela细胞,分别记为miR-196a inhibitor组、pcDNA-NR6A1组和inhibitor+NR6A1组,CCK8检测细胞增殖情况,流式细胞术检测细胞凋亡情况,Transwell检测细胞侵袭能力,划痕实验检测细胞迁移能力,免疫印迹检测Ki-67、Caspase-3、VEGF和MMP-9的表达。结果与HcerEpic细胞比较,Hela细胞和CaSki细胞中miR-196a和NR6A1 mRNA表达水平均较高(P<0.01),Hela细胞中miR-196a和NR6A1 mRNA表达变化最为显著(P<0.05);miR-196a inhibitor组Hela细胞中NR6A1蛋白表达显著降低(P<0.01),pcDNA-NR6A1组NR6A1的蛋白表达显著升高(P<0.01);miR-196a inhibitor能显著降低Hela细胞增殖倍数和Ki-67表达水平(P<0.05),同时还能提高Hela细胞凋亡率和Caspase-3表达(P<0.01);此外,miR-196a inhibitor还能减少侵袭细胞数,降低Hela细胞划痕闭合率并抑制VEGF和MMP-9的表达(P<0.01);NR6A1能显著减弱miR-196a inhibitor对Hela细胞增殖、凋亡、侵袭、迁移及对Ki-67、Casapse-3、VEGF和MMP-9表达的调控作用(P<0.01)。结论miR-196a inhibitor能通过靶向抑制NR6A1表达降低宫颈癌Hela细胞的生存和运动能力。     

A T cell activation antigen,Ly6C,induced on CD4+ Th1 cells mediates an inhibitory signal for secretion of IL-2 and proliferation in peripheral immune responses

A T cell activation antigen, Ly6C, is considered to be involved in the autoimmunity of some autoimmune-prone mice; however, the function of Ly6C remains largely unknown. We prepared a rat anti-mouse Ly6C monoclonal antibody (mAb) (S14) that inhibits the proliferation of peripheral T cells stimulated with anti-CD3 mAb in vitro. S14 mAb, the specificity of which is confirmed by a cDNA transfectant, recognizes Ly6C antigen preferentially expressed on a part of CD8⁺ T cells in peripheral lymphoid organs. The immunohistochemical analysis demonstrates that Ly6C appears on CD8⁺ T cells in the conventional T cell-associated area of BALB/c but not of nonobese diabetic (NOD) mice, confirming the absence of Ly6C⁺ T cells in NOD mice. Addition of soluble S14 mAb to the culture does not influence the proliferation of T cells in vitro; however, the S14 mAb coated on the plate clearly inhibits the proliferation and IL-2 production of anti-CD3-stimulated peripheral T cells. The T cells are arrested at the transitional stage from G₀/G₁ to S+G₂/M phases, but they are not induced to undergo apoptotic changes in vitro. This inhibitory signal provided through the Ly6C molecule inhibited IL-2 secretion in a subpopulation of the activated CD4⁺ T cells. Ly6C is expressed on T cell clones of both Th1 and Th2 cells, but the cytokine secretion from Th1 clones is preferentially inhibited. These results suggest that Ly6C mediates an inhibitory signal for secretion of cytokines from Th1 CD4⁺ T cells, potentially causing the inhibition of immune response in peripheral lymphoid tissues.     

IL‐4‐induced gene 1 maintains high Tob1 expression that contributes to TCR unresponsiveness in human T helper 17 cells

Human Th17 cells have a limited proliferative capacity compared to other T‐cell subsets. We have shown that human Th17 cells display impaired IL‐2 production due to IL‐4‐induced gene 1 (IL4I1) upregulation. Here, we show that in human Th17 cells, IL4I1 also maintains high levels of Tob1, a member of the Tob/BTG (B‐cell traslocation gene) antiproliferative protein family, which prevents cell‐cycle progression mediated by TCR stimulation. Indeed, Th17 cells exhibited higher levels of Tob1 than Th1 cells in both resting and TCR‐activated conditions. Accordingly, the expression of positive regulators of the cell cycle (cyclin A, B, C, and E and Cdk2), as well as of Skp2, which promotes Tob1 degradation, was lower in Th17 cells than in Th1 cells. Tob1 expression in human Th17 cells correlated with both RAR (retinoic acid receptor)‐related orphan receptor C (RORC) and IL4I1 levels. However, RORC was not directly involved in the regulation of Tob1 expression, whereas IL4I1 silencing in Th17 cells induced a substantial decrease of Tob1 expression. These data suggest that IL4I1 upregulation in human Th17 cells limits their TCR‐mediated expansion not only by blocking the molecular pathway involved in the activation of the IL‐2 promoter, but also by maintaining high levels of Tob1, which impairs entry into the cell cycle.     

The involvement of NR4A1 and NR4A2 in the regulation of the luteal function in rats

The nuclear receptor 4A (NR4A) members play important roles in cellular proliferation, differentiation and apoptosis. The current study first evaluate the expression of ovarian NR4A1 during different luteal stages in rats. Immature rats aged 28 days were treated with sequential Pregnant mare serum gonadotropin (PMSG) (D -2) / human chorionic gonadotropin (hCG) (D 0) to induce pseudopregnancy. Serum progesterone (P₄) and ovarian expression of NR4A1 were detected by RIA and WB, respectively, at follicle stage (D 0), early (D 2), middle (D 7) and late (D 14 and D 20) luteal stages. To confirm the role of NR4A1 during the luteal regression, rats were treated with prostaglandin F_2α analog (PGF) for 0–8?h on D 7 to detect the expressions of NR4A1 and NR4A2. RIA result showed that serum P₄ reached highest level on D 7 and then declined. WB results showed that there were two types of NR4A1 (NR4A1-L and NR4A1-S) expressed in the ovary. The ovarian NR4A1-L decreased at the late luteal stage (D 20). However, the NR4A1-S increased at the late luteal stage (D 14). After PGF treatment on D 7, the expression of NR4A1-S increased which peaked at 0.5–1?h and then declined; while NR4A1-L expression did not change within 8 h. Real-time PCR results showed that the ovarian NR4A1 mRNA increased within 0.5?h, maintained high at 1 h and then declined. The NR4A2 mRNA expression exhibited a similar pattern to that of NR4A1 mRNA, though its abundance was not as high as NR4A1. IHC results revealed that NR4A1-L was expressed mainly in the cytoplasm of luteal steroidogenic cells, faintly expressed in the follicle theca cells, oocytes and the pericytes; while NR4A2 was primarily localized in the cytoplasm of luteal steroidogenic cells. In conclusion, all these results demonstrate that NR4A2 as well as NR4A1 might be involved in the luteal development and luteolysis in rats.     

CCR4 and CXCR3 play different roles in the migration of T cells to inflammation in skin,arthritic joints,and lymph nodes

CCR4 and CXCR3 are expressed on several T‐cell subsets in inflamed tissues, yet their role in tissue‐specific recruitment is unclear. We examined the contributions of CCR4 and CXCR3 to T‐cell recruitment into inflamed joints in collagen‐induced arthritis, antigen‐draining lymph nodes (LNs) and dermal inflammatory sites (poly I:C, LPS, concanavalin A, and delayed type hypersensitivity), using labeled activated T cells from CXCR3^?/?, CCR4^?/?, and WT mice. Both CXCR3 and CCR4 deficiency reduced the development of arthritis, but did not affect Th1‐cell recruitment to the inflamed joints. Accumulation in inflamed LNs was highly CXCR3 dependent. In contrast, CCR4‐deficient Th1 cells had an increased accumulation in these LNs. Migration to all four dermal inflammatory sites by activated Th1 and T cytotoxic cells and memory CD4⁺ T cells was partially CXCR3‐dependent, but Treg‐cell migration was independent of CXCR3. The subset of cells expressing CCR4 has skin‐migrating properties, but CCR4 itself is not required for the migration. Thus, migration into these inflamed tissues is CCR4‐independent, and partially dependent on CXCR3, except for Treg cells, which require neither receptor. CCR4 may therefore affect retention of T cells in different tissues rather than trafficking out of the blood.     

Involvement of CD91 and scavenger receptors in Hsp70‐facilitated activation of human antigen‐specific CD4+ memory T cells

Hsp70 plays several roles in the adaptive immune response. Based on the ability to interact with diverse peptides, extracellular Hsp70:peptide complexes exert profound effects both in autoimmunity and in tumor rejection by evoking potent T cell responses to the chaperoned peptide. The interaction with receptors on APC represents the basis for the immunological functions of Hsp70 and a critical point where the immune response can be regulated. Various surface proteins (e.g. CD91, scavenger receptors (SR)) have been implicated in binding of Hsp70. In this study, antigenic peptides from tetanus toxin and influenza hemagglutinin complexed to human stress‐inducible Hsp70 were found to enhance the proliferation and cytokine production of human antigen‐specific CD4⁺ T cells. This was demonstrated in proliferation experiments using human monocytes as APC. Proliferated antigen‐specific cells were detected combining HLA‐DRB1^*0401 or HLA‐DRB1^*1101 tetramer and CFSE staining. Treating monocytes with CD91 siRNA diminished these effects. Additional blocking of SR by the SR ligand fucoidan completely abolished enhanced proliferation and production of Th1 and Th2 cytokines. Taken together, our data indicate that in the human system, CD91 and members of the SR family efficiently direct Hsp70:peptide complexes into the MHC class II presentation pathway and thus enhance antigen‐specific CD4⁺ T cell responses.     

IL‐4 blocks M‐CSF‐dependent macrophage proliferation by inducing p21Waf1 in a STAT6‐dependent way

Macrophages are recruited from the blood stream to the inflammatory loci to carry out their functional activities. In an early phase of the cell cycle, macrophages become activated by Th1‐type cytokines (i.e. IFN‐γ), thereby producing several factors (cytokines, NO, etc.) and developing pro‐inflammatory activities. When bacteria and apoptotic bodies are removed, through the interaction with Th2‐type cytokines (i.e. IL‐4), macrophages become anti‐inflammatory and repair damaged tissues. Incubation of bone‐marrow‐derived macrophages with IFN‐γ or IL‐4 blocked their proliferation. While M‐CSF withdrawal caused cell cycle arrest at the early G₁ phase, treatment of macrophages with IFN‐γ or IL‐4 caused this arrest later, at the G₁/S boundary. Proliferation arrest was not due to an induction of apoptosis. IFN‐γ and IL‐4 induced the expression of the cyclin‐dependent kinase (Cdk) inhibitor p21^Waf1. Using KO mice and iRNA experiments, we found that p21^Waf1is required for IL‐4‐ but not for IFN‐γ‐dependent inhibition of macrophage proliferation. IL‐4 inhibited M‐CSF‐dependent Cdk‐2 and Cdk‐4 activities, which are necessary for entry and passage through the S phase of the cell cycle. The signal transduction used to induce the expression of p21^Waf1after interaction of IL‐4 with the corresponding receptor was mediated by STAT6. Thus, IL‐4 and IFN‐γ blocked M‐CSF‐induced macrophage proliferation through distinct mechanisms.     

Biphasic role of 4‐1BB in the regulation of mouse cytomegalovirus‐specific CD8+ T cells

The initial requirement for the emergence of CMV‐specific CD8⁺ T cells is poorly understood. Mice deficient in the cosignaling TNF superfamily member, 4‐1BB, surprisingly developed exaggerated early CD8⁺ T‐cell responses to mouse CMV (MCMV). CD8⁺ T cells directed against acute MCMV epitopes were enhanced, demonstrating that 4‐1BB naturally antagonizes these primary populations. Paradoxically, 4‐1BB‐deficient mice displayed reduced accumulation of memory CD8⁺ T cells that expand during chronic/latent infection. Importantly, the canonical TNF‐related ligand, 4‐1BBL, promoted the accumulation of these memory CD8⁺ T cells, whereas suppression of acute CD8⁺ T cells was independent of 4‐1BBL. These data highlight the dual nature of the 4‐1BB/4‐1BBL system in mediating both stimulatory and inhibitory cosignaling activities during the generation of anti‐MCMV immunity.     

IL‐12 and IL‐4 activate a CD39‐dependent intrinsic peripheral tolerance mechanism in CD8+ T cells

Immune responses to protein antigens involve CD4⁺ and CD8⁺ T cells, which follow distinct programs of differentiation. Naïve CD8 T cells rapidly develop cytotoxic T‐cell (CTL) activity after T‐cell receptor stimulation, and we have previously shown that this is accompanied by suppressive activity in the presence of specific cytokines, i.e. IL‐12 and IL‐4. Cytokine‐induced CD8⁺ regulatory T (Treg) cells are one of several Treg‐cell phenotypes and are Foxp3^? IL‐10⁺ with contact‐dependent suppressive capacity. Here, we show they also express high level CD39, an ecto‐nucleotidase that degrades extracellular ATP, and this contributes to their suppressive activity. CD39 expression was found to be upregulated on CD8⁺ T cells during peripheral tolerance induction in vivo, accompanied by release of IL‐12 and IL‐10. CD39 was also upregulated during respiratory tolerance induction to inhaled allergen and on tumor‐infiltrating CD8⁺ T cells. Production of IL‐10 and expression of CD39 by CD8⁺ T cells was independently regulated, being respectively blocked by extracellular ATP and enhanced by an A2A adenosine receptor agonist. Our results suggest that any CTL can develop suppressive activity when exposed to specific cytokines in the absence of alarmins. Thus negative feedback controls CTL expansion under regulation from both nucleotide and cytokine environment within tissues.     

CCR6 and NK1.1 distinguish between IL‐17A and IFN‐γ‐producing γδ effector T cells

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24^low CD44^high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6⁺ γδ T cells produced IL‐17A, while NK1.1⁺ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1⁺ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1⁺ or CCR6⁺ γδ T cells, respectively. Importantly, we show that CCR6⁺ γδ T cells are more responsive to TCR stimulation than their NK1.1⁺ counterparts. In conclusion, our findings support the hypothesis that CCR6⁺ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1⁺ γδ T cells.     

Functional and molecular characterization of B cell-responsive Vδ1+ γδ T cells

Cells expressing the Vδ1⁺ gene segment are a minor γδ T cell population in human peripheral blood but predominate in epithelia and (inflamed) tissues. The characteristic dendritic-like morphology of these γδ T cells is consistent with their putative immune surveillance role in epithelia. Their function, however, remains unknown. We and others previously reported that a subset of Vδ1⁺ γδ T cells proliferates after stimulation with Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (LCL), but not with fresh peripheral blood-derived B cells. These responses were independent of the type of T cell receptor (TcR) γ chain co-expressed with the Vδ1 chain. The in vivo relevance of this LCL-mediated activation as well as the nature of the stimulatory ligand on the LCL is not well established. In this study, we tested the proliferative response of Vδ1⁺ LCL-responsive T cells against non-EBV-transformed B cells, activated through CD40 by murine EL4 B5 cells, and to a panel of B cell lines differing in the expression of EBV nuclear antigen proteins and adhesion/co-stimulatory molecules. The role of the Epstein-Barr virus-derived antigen in the induction of this response could be excluded as the activated (non-EBV-transformed) peripheral blood B cells were also able to induce a proliferative response in the LCL-responsive Vδ1⁺ T cells. Therefore, the stimulatory ligand on B cells is of cellular rather than of viral origin, and its expression is up-regulated upon activation of B cells. The expression of B7 and CD39 molecules on the surface of activated B cells appeared to be crucial since antibodies to these structures could block the induction of proliferation of the Vδ1⁺ T cells. Finally, we investigated the diversity of the responding Vδ1⁺ γδ T cell clones by sequence analysis of the TcRδ junctional regions. No restricted V-D-J sequences were found among the LCL-responsive Vδ1⁺ T cell clones, arguing strongly against a mono- or oligoclonal Vδ1⁺ γδ T cell response to LCL. These findings may explain the presence of polyclonally activated Vδ1⁺ T cells in inflamed tissues where activated B cells are often present.     

CD11c+ CD103+ cells of Mycobacterium tuberculosis‐infected C57BL/6 but not of BALB/c mice induce a high frequency of interferon‐γ‐ or interleukin‐17‐producing CD4+ cells

The magnitude of the cellular adaptive immune response is critical for the control of Mycobacterium tuberculosis infection in the chronic phase. In addition, the genetic background is equally important for resistance or susceptibility to tuberculosis. In this study, we addressed whether lung populations of dendritic cells, obtained from genetically different hosts, would play a role in the magnitude and function of CD4⁺ populations generated after M. tuberculosis infection. Thirty days post-infection, C57BL/6 mice, which generate a stronger interferon-γ (IFN-γ)-mediated immune response than BALB/c mice, exhibited a higher number and frequency of lung CD11c⁺ CD11b⁻ CD103⁺ cells compared with BALB/c mice, which exhibited a high frequency of lung CD11c⁺ CD11b⁺ CD103⁻ cells. CD11c⁺ CD11b⁻ CD103⁺ cells, purified from lungs of infected C57BL/6 mice, but not from infected BALB/c mice, induced a higher frequency of IFN-γ-producing or interleukin-17 (IL-17)-producing CD4⁺ cells. Moreover, CD4⁺ cells also arrive at the lung of C57BL/6 mice faster than in BALB/c mice. This pattern of immune response seems to be associated with higher gene expression for CCL4, CCL19, CCL20 and CCR5 in the lungs of infected C57BL/6 mice compared with infected BALB/c mice. The results described here show that the magnitude of IFN-γ-producing or IL-17-producing CD4⁺ cells is dependent on CD11c⁺ CD11b⁻ CD103⁺ cells, and this pattern of immune response is directly associated with the host genetic background. Therefore, differences in the genetic background contribute to the identification of immunological biomarkers that can be used to design human assays to predict progression of M. tuberculosis infection.     

Sphingosine‐1‐phosphate receptor 1 signalling in T cells: trafficking and beyond

Sphingosine-1-phosphate (S1P) is a lipid second messenger that signals via five G protein-coupled receptors (S1P_1–5). S1P receptor (S1PR) signalling is associated with a wide variety of physiological processes including lymphocyte biology, their recirculation and determination of T-cell phenotypes. The effect of FTY720 (Fingolimod, Gilenya™) to regulate lymphocyte egress and to ameliorate paralysis in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis led to the use of FTY720 as a first-line oral agent for treatment of relapsing–remitting multiple sclerosis. However, a significant body of research suggests that S1P signalling may participate in diverse immune regulatory functions other than lymphocyte trafficking. This review article discusses the current knowledge of S1P signalling in the fate and function of T regulatory, T helper type 17 and memory T cells in health and disease.     

Autoimmune arthritis induces paired immunoglobulin‐like receptor B expression on CD4+ T cells from SKG mice

The chronic, destructive autoimmune arthritis in SKG mice, which closely resembles human rheumatoid arthritis, is the result of self‐reactive T cells escaping thymic deletion. Since the inhibitory receptor LIR‐1 is up‐regulated on auto‐reactive T cells in human rheumatoid arthritis, the role of its murine ortholog PIR‐B was investigated. Peripheral CD4⁺ T cells from SKG mice were found to frequently express PIR‐B, and this population produces more frequently IL‐17 upon in vitro stimulation compared to PIR‐B^? cells. A much larger fraction of PIR‐B⁺ T cells, however, was found to secret no IL‐17, but IFN‐γ. With regards to the clinical course of the disease, high frequencies of PIR‐B⁺ CD4⁺ T cells were found to be associated with a milder course of arthritis, suggesting that the net effect of PIR‐B expression is suppression of autoreactive T cells. Our results indicate that overexpression of PIR‐B on IL‐17‐producing SKG CD4⁺ T cells might represent an effective counter‐regulatory mechanism against the destructive potential of those cells. More importantly, a major population of PIR‐B⁺ T cells in SKG mice appears to play an inhibitory role by way of their IFN‐γ production, since high frequencies of those cells ameliorate the disease.