T regulatory cells (T regs ) can activate multiple suppressive mechanisms in vitro upon activation via the T cell receptor resulting in antigen-independent suppression. However, it remains unclear whether similar pathways operate in vivo. Here, we found that antigen-specific T regs activated by dendritic cells (DCs) pulsed with two antigens suppressed T naive specific for both cognate and non-cognate antigens in vitro, but only suppressed T naive specific for cognate antigen in vivo. Antigen-specific T regs formed strong interactions with DC resulting in selective inhibition of the binding of T naive to cognate antigen, yet allowing bystander T naive access. Strong binding resulted in removal of the cognate peptide-MHCII (pMHCII) from the DC surface reducing the capacity of the DC to present antigen. The enhanced binding of T regs to DC coupled with their capacity to deplete pMHCII represents a novel pathway for T reg -mediated suppression and may be a mechanism by which T regs maintain immune homeostasis.

Objective. B and T lymphocyte attenuator (BTLA), a coreceptor expressed on lymphocytes, was recently described as an inhibitory coreceptor that negatively regulates lymphocyte activation. The purpose of this study was to investigate the role of BTLA in the regulation of immune homeostasis and the pathogenesis of autoimmunity.Methods. We examined the levels of immunoglobulins and autoantibodies to nuclear antigens and the activation status of T cells in BTLA ؊/؊ mice. We also examined histopathologic changes in the organs of BTLA ؊/؊ mice. Results. We observed that BTLA ؊/؊ mice gradually developed hypergammaglobulinemia, antinuclear antibodies, anti-SSA antibodies, anti-double-stranded DNA antibodies, and an increased number of activated CD4؉ T cells in the periphery with age. Lack of BTLA led to spontaneous development of autoimmune hepatitis-like disease characterized by an elevation in the level of transaminases, interface hepatitis, and spotty necrosis of the liver. BTLA ؊/؊ mice also showed inflammatory cell infiltration of multiple organs, including the salivary glands, lungs, and pancreas; these features are similar to those of Sjögren's syndrome, which is a frequent complication of autoimmune hepatitis. Furthermore, the survival rate of BTLA ؊/؊ mice was significantly reduced after the age of 7 months.Conclusion. Our results indicate that BTLA plays an important role in the maintenance of immune tolerance and the prevention of autoimmune diseases.

Background: Lacrimal gland enlargement (LGE) is one of the characteristics of Mikulicz’s disease (MD). Recently, marked serum IgG4 elevation and infiltration of IgG4-positive plasmacytes in the enlarged exocrine glands have been reported in MD patients. However, little is known about the role of CD4+ T cells and their cytokines in IgG4-related diseases. The aim of this study was to evaluate the characteristics of CD4+ T cells in patients with IgG4-related diseases. Methods: We investigated the clinical characteristics of 9 patients with LGE and elevated serum IgG4 levels (named IgG4-related LGE). We also examined mRNA expression of cytokines and transcription factors of peripheral blood CD4+ T cells in patients with IgG4-related LGE. Results: All patients with IgG4-related LGE showed elevated serum IgE levels. In addition, 5 of 9 patients with IgG4-related LGE exhibited eosinophilia and asthma-like symptoms. In patients with IgG4-related LGE, mRNA expression of IL-4, IL-5, IL-10 and GATA-3 but not IFN-γ or T-bet was enhanced on CD4+ T cells compared with that in healthy controls. Conclusions: Th2 cells may be involved in the pathogenesis of IgG4-related diseases.

Inhibitory coreceptors are thought to play important roles in maintaining immunological homeostasis, and a defect in the negative signals from inhibitory coreceptors may lead to the development of autoimmune diseases. We have recently identified B and T lymphocyte attenuator (BTLA), a new inhibitory coreceptor expressed on immune cells, and we suggest that BTLA may be involved in the development of autoimmune diseases using BTLA-deficient mice. However, the role of BTLA in the pathogenesis of autoimmune diseases in humans remains unknown. We, therefore, examined the possible association between BTLA and rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and Sjögren's syndrome (SS) by conducting a case-control genetic association study. We found that 590C single-nucleotide polymorphism (SNP) of BTLA gene was significantly associated with susceptibility to RA, but not to SLE or SS. Furthermore, RA patients bearing this 590C SNP developed the disease significantly earlier than the patients without this allele. We also found that BTLA with 590C allele lacked the inhibitory activity on concanavalin A- and anti-CD3 Ab-induced IL-2 production in Jurkat T cells. These results suggest that BTLA is an RA-susceptibility gene and is involved in the protection from autoimmunity in humans.

Although B and T lymphocyte attenuator (BTLA) was originally identified as an inhibitory coreceptor selectively expressed on Th1 cells and B cells, recent studies have revealed that BTLA is expressed on a variety of cells, including macrophages, dendritic cells, and NK cells, and modulates their functions. However, the role of BTLA in the regulation of NKT cell function remains unknown. In this study, we found that BTLA was expressed on NKT cells at the levels similar to those on T cells and that BTLA-deficient (BTLA−/−) NKT cells produced larger amounts of IL-4 and IFN-γ upon α-glactosylceramide stimulation as compared with wild-type (WT) NKT cells. In vivo, BTLA−/− mice produced larger amounts of IL-4 and IFN-γ upon Con A injection and were more susceptible to Con A-induced hepatitis than WT mice. In addition, the augmentation of Con A-induced hepatitis in BTLA−/− mice was not observed in BTLA/NKT-double deficient mice. Moreover, NKT−/− mice reconstituted with BTLA−/− NKT cells were significantly more susceptible to Con A-induced hepatitis as compared with NKT −/− mice reconstituted with WT NKT cells. These results suggest that BTLA functions as the inhibitory coreceptor of NKT cells and plays a critical role in the prevention of NKT cell-mediated liver injury.

MRL/Mp-Fas (lpr) (MRL-lpr) mice develop a systemic autoimmune disease and are considered to be a good model for systemic lupus erythematosus in humans. We have recently shown that mice lacking B and T lymphocyte attenuator (BTLA), an inhibitory co-receptor expressed mainly on lymphocytes, on a 129SvEv background spontaneously develop lymphocytic infiltration in multiple organs and an autoimmune hepatitis (AIH)-like disease. In this study, we investigated the role of BTLA in the pathogenesis of autoimmune diseases in MRL-lpr mice. We found that BTLA-deficient (BTLA(-/-)) MRL-lpr/lpr mice developed severe lymphocytic infiltration in salivary glands, lungs, pancreas, kidneys and joints as compared with BTLA-sufficient (BTLA(+/+)) MRL-lpr/lpr mice. In addition, although AIH-like disease was not found in BTLA(+/+) MRL-lpr/lpr mice, AIH-like disease was exacerbated in BTLA(-/-) MRL-lpr/lpr mice as compared with that in BTLA(-/-) 129SvEv mice. These results suggest that BTLA plays a protective role in autoimmune diseases in MRL-lpr mice and that AIH-like disease develops in BTLA(-/-) mice even in the absence of Fas-dependent signaling.

BTLA, a recently cloned coreceptor expressed on lymphocytes, negatively regulates cell activation by recruiting SHP-1/SHP-2. However, the mechanisms that regulate the intracellular localization of BTLA and its trafficking to the cell surface in T cells are still unknown. To determine the mechanisms that regulate the expression of BTLA on the surface of T cells, we examined the subcellular localization of BTLA in mouse T cells in a steady state, as well as upon activation by using a confocal laser-scanning microscopy. We found that BTLA was localized mainly in the Golgi apparatus and secretory lysosomes in resting CD4(+) T cells. We also found that intracellular BTLA was translocated to the cell surface and accumulated at the immunological synapse upon TCR stimulation. Furthermore, we found that the BTLA-HVEM interaction was required for the association of BTLA with lipid rafts. These results indicate that the surface expression of BTLA and its accumulation at the immunological synapse are tightly regulated by TCR and HVEM stimulation to deliver efficient inhibitory signals in the regulation of CD4(+) T cell activation.

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