Autoantigen-specific CD4+CD28low T cell subset prevents autoimmune exocrinopathy in murine Sjögren's syndrome

Pathology of salivary gland dysfunction and restoration of function

In this review, the author shows that simultaneous multiple disorders caused by reactivation of Epstein-Barr virus can lead to salivary gland disorders as part of Sjogren's syndrome (SS). Therefore, clinicians must differentiate SS from other diseases when diagnosing and treating salivary gland disorders. In particular, the author explains how microbial infection in SS overcomes immunological tolerance, leading to pathological changes, and how cytokine overexpression and endocrine disrupters contribute to glandular tissue injury. Also, the author suggests that involvement of reactive oxygen species is a common pathogenesis of salivary gland disorders and SS, so regulation of oxidative stress is an effective treatment for both. The results of clinical studies on restoring salivary gland function and regenerating salivary glands with tissue stem cells may provide clues on elucidating the cause of SS.

Pathological Analysis of Ocular Lesions in a Murine Model of Sjögren's Syndrome

Sjögren’s syndrome (SS) is a systemic autoimmune disease characterized by severe inflammation of exocrine glands such as the salivary and lacrimal glands. When it affects the lacrimal glands, many patients experience keratoconjunctivitis due to severely dry eyes. This study investigated the pathological and immunological characteristics of ocular lesions in a mouse model of SS. Corneal epithelial injury and hyperplasia were confirmed pathologically. The number of conjunctival mucin-producing goblet cells was significantly decreased in the SS model mice compared with control mice. Expression levels of transforming growth factor (TGF)-β, interleukin (IL)-6, tumor necrosis factor (TNF)-α, and C-X-C motif chemokine (CXCL) 12 were significantly higher in the corneal epithelium of the SS model mice than in control mice. Inflammatory lesions were observed in the Harderian, intraorbital, and extraorbital lacrimal glands in the SS model mice, suggesting that the ocular glands were targeted by an autoimmune response. The lacrimal glands of the SS model mice were infiltrated by cluster of differentiation (CD)4⁺ T cells. Real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed significantly increased mRNA expression of TNF-α, TGF-β, CXCL9, and lysozyme in the extraorbital lacrimal glands of the SS model mice compared with control mice. These results add to the understanding of the complex pathogenesis of SS and may facilitate development of new therapeutic strategies.

Mouse Models of Primary Sjogren's Syndrome

Sjogren's syndrome (SjS) is a chronic autoimmune disorder characterized by immune cell infiltration and progressive injury to the salivary and lacrimal glands. As a consequence, patients with SjS develop xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). SjS is the third most common rheumatic autoimmune disorder, affecting 4 million Americans with over 90% of patients being female. Current diagnostic criteria for SjS frequently utilize histological examinations of minor salivary glands for immune cell foci, serology for autoantibodies, and dry eye evaluation by corneal or conjunctival staining. SjS can be classified as primary or secondary SjS, depending on whether it occurs alone or in association with other systemic rheumatic conditions, respectively. Clinical manifestations typically become apparent when the disease is relatively advanced in SjS patients, which poses a challenge for early diagnosis and treatment of SjS. Therefore, SjS mouse models, because of their close resemblance to the human SjS, have been extremely valuable to identify early disease markers and to investigate underlying biological and immunological dysregulations. However, it is important to bear in mind that no single mouse model has duplicated all aspects of SjS pathogenesis and clinical features, mainly due to the multifactorial etiology of SjS that includes numerous susceptibility genes and environmental factors. As such, various mouse models have been developed in the field to try to recapitulate SjS. In this review, we focus on recent mouse models of primary SjS xerostomia and describe them under three categories of spontaneous, genetically engineered, and experimentally induced models. In addition, we discuss future perspectives highlighting pros and cons of utilizing mouse models and current demands for improved models.

Immune checkpoint receptors in regulating immune reactivity in rheumatic disease

Immune checkpoint regulators are critical modulators of the immune system, allowing the initiation of a productive immune response and preventing the onset of autoimmunity. Co-inhibitory and co-stimulatory immune checkpoint receptors are required for full T-cell activation and effector functions such as the production of cytokines. In autoimmune rheumatic diseases, impaired tolerance leads to the development of diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjogren’s syndrome. Targeting the pathways of the inhibitory immune checkpoint molecules CD152 (cytotoxic T lymphocyte antigen-4) and CD279 (programmed death-1) in cancer shows robust anti-tumor responses and tumor regression. This observation suggests that, in autoimmune diseases, the converse strategy of engaging these molecules may alleviate inflammation owing to the success of abatacept (CD152-Ig) in rheumatoid arthritis patients. We review the preclinical and clinical developments in targeting immune checkpoint regulators in rheumatic disease.

Anti-inflammatory effects of rebamipide eyedrop administration on ocular lesions in a murine model of primary Sjögren's syndrome

BACKGROUND

Topical therapy is effective for dry eye, and its prolonged effects should help in maintaining the quality of life of patients with dry eye. We previously reported that the oral administration of rebamipide (Reb), a mucosal protective agent, had a potent therapeutic effect on autoimmune lesions in a murine model of Sjögren's syndrome (SS). However, the effects of topical treatment with Reb eyedrops on the ocular lesions in the murine model of SS are unknown.

METHODS AND FINDING

Reb eyedrops were administered to the murine model of SS aged 4-8 weeks four times daily. Inflammatory lesions of the extraorbital and intraorbital lacrimal glands and Harderian gland tissues were histologically evaluated. The direct effects of Reb on the lacrimal glands were analyzed using cultured lacrimal gland cells. Tear secretions of Reb-treated mice were significantly increased compared with those of untreated mice. In addition to the therapeutic effect of Reb treatment on keratoconjunctivitis, severe inflammatory lesions of intraorbital lacrimal gland tissues in this model of SS were resolved. The mRNA expression levels of IL-10 and mucin 5Ac in conjunctival tissues from Reb-treated mice was significantly increased compared with those of control mice. Moreover, lactoferrin production from lacrimal gland cells was restored by Reb treatment.

CONCLUSION

Topical Reb administration had an anti-inflammatory effect on the ocular autoimmune lesions in the murine model of SS and a protective effect on the ocular surfaces.

Long time follow up of CD28- CD4+ T cells in living kidney transplant patients

We previously reported that the CD28(-) CD4(+) T cell subpopulation was expanded in the kidney allograft patients with long graft survival, although these T cells were rarely found in patients with graft survival <5 yr. To understand the CD28(-) CD4(+) T cells in the long-term acceptance of kidney allografts, we examined functions of this population and performed a 4 yr follow up study. Peripheral blood mononuclear cells (PBMC) were obtained from 47 long-term living related kidney allograft recipients. CD28(+) CD4(+) and CD28(-) CD4(+) T cells purified by cell sorting were analyzed for expression of V(beta) repertoire. Donor-specific response was examined in mixed lymphocyte reaction (MLR). A follow up study with long-term kidney allograft patients was performed for 4 yr about the rate of CD28(-) CD4(+) T cells. Eleven patients were examined by MLRs against donors and third party. Four patients with a marked increase of CD28(-) CD4(+) T cells showed the donor-specific responses appeared to be lower when compared with third party-specific responses. Freshly sorted CD28(-) CD4(+) T cells showed a restricted V(beta) repertoire, whereas the V(beta) usage of CD28(+) CD4(+) T cells from the same patients was much diversified. Such difference in V(beta) repertoire was not evident between the two populations from healthy control. A follow up study showed the ratio of CD28(-) CD4(+) T cells appeared to be lower in patients who were suspected of chronic rejection. These unusual CD4(+) T cells might be related to the long-term acceptance of human transplant allografts.

Estrogen deficiency accelerates murine autoimmune arthritis associated with receptor activator of nuclear factor-kappa B ligand-mediated osteoclastogenesis

The aims of this study were to evaluate the in vivo effects of estrogen deficiency in MRL/lpr mice as a model for rheumatoid arthritis and to analyze the possible relationship between immune dysregulation and receptor activator of nuclear factor-kappaB ligand (RANKL)-mediated osteoclastogenesis. Experimental studies were performed in ovariectomized (Ovx)-MRL/lpr, Ovx-MRL+/+, sham-operated-MRL/lpr, and sham-operated-MRL+/+ mice. Severe autoimmune arthritis developed in younger Ovx-MRL/lpr mice until 24 wk of age, whereas these lesions were entirely recovered by pharmacological levels of estrogen administration. A significant elevation in serum rheumatoid factor, anti-double-stranded DNA, and anti-type II collagen was found in Ovx-MRL/lpr mice and recovered in mice that underwent estrogen administration. A high proportion of CD4(+) T cells bearing RANKL was found, and an enhanced expression of RANKL mRNA and an impaired osteoprotegerin mRNA was detected in the synovium. An increase in both osteoclast formation and bone resorption pits was found. These results indicate that estrogen deficiency may play a crucial role in acceleration of autoimmune arthritis associated with RANKL-mediated osteoclastogenesis in a murine model for rheumatoid arthritis.

Genomic absence of the gene encoding T cell receptor Vbeta7.2 is linked to the presence of autoantibodies in Sjögren's syndrome

OBJECTIVE

It is not yet known whether the absence of certain T cell receptor V(beta) (TCRBV) genes (e.g., due to genomic deletion) has functional significance. We examined this question in relation to a known 21.6-kb insertion/deletion-related polymorphism (IDRP) in the human BV locus.

METHODS

New polymerase chain reaction (PCR) genotyping methods were used. Monoclonal antibodies to TCRBV gene products were used to confirm the absence of the relevant proteins. Patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE) were compared with normal controls with regard to TCR genotypes and serologic profiles.

RESULTS

There are 3 known haplotypes (I, D1, D2) and 6 possible genotypes related to the 21.6-kb IDRP. Novel PCR-based methods were used to define these genotypes. In subjects with deleted/deleted (D/D) genotypes, T cells could not express V(beta)7.2 TCRs, as assayed with a new antibody specific for V(beta)7.2. This was the sole significant difference between subjects without the insertion and those with either 1 or 2 copies. Surprisingly, we found that the D/D genotype was associated with primary SS, but only when pathogenic autoantibodies were present.

CONCLUSION

These results suggest that T cells expressing TCRs with V(beta)7.2 are protective against a pathogenic immune response in SS. Thus, genomic polymorphism of TCR genes (along with the correct HLA alleles) determines whether T cells can direct a pathogenic autoimmune response.

Development of autoimmune exocrinopathy resembling Sjögren's syndrome in adoptively transferred mice with autoreactive CD4+ T cells

OBJECTIVE

The pathologic mechanisms responsible for organ-specific tissue damage in primary Sjögren's syndrome (SS) remain unclear, but it has been suggested that the pathology is mediated by autoreactive CD4+ T cells infiltrating the salivary and lacrimal glands. This study was undertaken to investigate whether alpha-fodrin autoantigen-specific autoreactive CD4+ T cells are capable of inducing autoimmune lesions.

METHODS

A total of 45 synthetic alpha-fodrin peptides designed to be 20 amino acid residues in length were generated. To establish an autoreactive T cell line, limiting dilution analysis (LDA) was performed on lymph node cells (LNCs) in the presence of alpha-fodrin peptides. The effects of adoptive transfer of autoreactive CD4+ T cells into normal syngeneic recipients were investigated.

RESULTS

Autoreactive CD4+ T cell lines that recognize synthetic alpha-fodrin peptide, which produced Th1 cytokines and showed cytotoxic activities, were established in a murine model for SS. T cell receptor V(beta) usage and third complementarity-determining region (CDR3) sequences indicated that in some cases V(beta)6-CDR3 genes matched between the tissue-infiltrating T cells and the autoreactive T cell lines. Adoptive transfer of the autoreactive CD4+ T cells into normal syngeneic recipients induced autoimmune lesions quite similar to those of SS.

CONCLUSION

Our data help to elucidate the pathogenic mechanisms responsible for tissue destruction in autoimmune exocrinopathy and indicate that autoreactive CD4+ T cells play a pivotal role in the development of murine SS.

Cathepsin S inhibitor prevents autoantigen presentation and autoimmunity

The cysteine endoprotease cathepsin S mediates degradation of the MHC class II invariant chain Ii in human and mouse antigen-presenting cells. Studies described here examine the functional significance of cathepsin S inhibition on autoantigen presentation and organ-specific autoimmune diseases in a murine model for Sjögren syndrome. Specific inhibitor of cathepsin S (Clik60) in vitro markedly impaired presentation of an organ-specific autoantigen, 120-kDa alpha-fodrin, by interfering with MHC class II-peptide binding. Autoantigen-specific T cell responses were significantly and dose-dependently inhibited by incubation with Clik60, but not with inhibitor s of cathepsin B or L. Clik60 treatment of mouse salivary gland cells selectively inhibited autopeptide-bound class II molecules. Moreover, the treatment with Clik60 in vivo profoundly blocked lymphocytic infiltration into the salivary and lacrimal glands, abrogated a rise in serum autoantibody production, and led to recovery from autoimmune manifestations. Thus, inhibition of cathepsin S in vivo alters autoantigen presentation and development of organ-specific autoimmunity. These data identify selective inhibition of cysteine protease cathepsin S as a potential therapeutic strategy for autoimmune disease processes.

Characterization of CD28(-)CD4(+) T cells in living kidney transplant patients with long-term allograft acceptance

CD28(-)CD4(+) T-cell subpopulation is expanded in kidney allograft patients with long graft survival. To seek for the roles of CD28(-)CD4(+) T cells in the long-term acceptance of kidney allografts, we characterized this population by analyzing cell surface molecules, TCR V(beta) repertoire, mixed lymphocyte reaction (MLR), and cytokine production. The number of CD28(-)CD4(+) T cells increased correlatively with time after transplantation in this group of patients. The CD28(-)CD4(+) T cells did not express detectable levels of CD25, CD69, V(alpha)24, or CTLA-4 but expressed heterogeneous amounts of CD45 RA on the surface. Freshly sorted CD28(-)CD4(+) T cells revealed a restricted V(beta) repertoire, whereas the V(beta) usage of CD28(+)CD4(+) T cells from the same patients was much diversified. Expression levels of TGF-beta and IFNgamma gene were significantly higher in the CD28(-) CD4(+) T cells than in the CD28(+)CD4(+) T cells from the kidney allograft patients. These findings suggest that an oligoclonal CD28(-) CD4(+) T-cell population is continuously activated in patients with long allograft survival, which may be linked with the long-term acceptance.