Type I and II interferons commit to abnormal expression of chemokine receptor on B cells in patients with systemic lupus erythematosus.

Memory B cells are increased in systemic lupus erythematosus (SLE) cases, but the qualitative abnormalities and induction mechanism of these cells are unclear. Here, we subclassified B cells by their chemokine receptor expression and investigated their induction mechanism. The peripheral blood of patients with SLE showed higher levels of CXCR5- and CXCR3+ B cells. CXCR5-CXCR3+ B cell levels were elevated in patients with active SLE, which decreased with improving disease conditions. Interferon (IFN)-γ stimulation increased CXCR3 expression, whereas IFN-ß stimulation reduced CXCR5 expression in B cells. Furthermore, CXCR5-CXCR3+ B cells were induced by a combination of IFN-ß and IFN-γ stimulation. Renal tissue examination of patients with active lupus nephritis confirmed the presence of CD19+CXCR3+ B cells. Collectively, the results revealed qualitative abnormalities accompanying reduced CXCR5 expression via type I IFN and enhanced CXCR3 expression via type II IFN in SLE, suggesting their involvement in B cell infiltration into tissues and inflammatory pathogenesis.

Amplification of IL-21 signalling pathway through Bruton's tyrosine kinase in human B cell activation.

OBJECTIVE: B cells play an important role in the pathogenesis of autoimmune diseases. The role of Bruton's tyrosine kinase (Btk) in cytokine-induced human B cell differentiation and class-switch recombination remains incompletely defined. This study analysed the effect of Btk on human activated B cells. METHODS: Purified B cells from healthy subjects were stimulated with B cell receptor (BCR) and other stimuli with or without a Btk inhibitor and gene expression was measured. The B cell line BJAB was used to assess Btk-associated signalling cascades. Phosphorylated Btk (p-Btk) in peripheral blood B cells obtained from 10 healthy subjects and 41 patients with RA was measured by flow cytometry and compared with patient backgrounds. RESULTS: IL-21 signalling, in concert with BCR, CD40 and BAFF signals, led to robust expression of differentiation- and class-switch DNA recombination-related genes and IgG production in human B cells, all of which were significantly suppressed by the Btk inhibitor. Although phosphorylation of STAT1 and STAT3 was induced by co-stimulation with IL-21, BCR and CD40, STAT1 phosphorylation in the nucleus, but not in the cytoplasm, was exclusively impaired by Btk blockade. High levels of p-Btk were noted in B cells of RA patients compared with controls and they correlated significantly with titres of RF among RF-positive patients. CONCLUSION: The findings elucidate a model in which Btk not only plays a fundamental role in the regulation of BCR signalling, but may also mediate crosstalk with cytokine signalling pathways through regulation of IL-21-induced phosphorylation of STAT1 in the nuclei of human B cells. Btk appears to have pathological relevance in RA.

Amplification of Toll-like receptor-mediated signaling through spleen tyrosine kinase in human B-cell activation.

BACKGROUND: B cells are activated by combined signals through the B-cell receptor (BCR) and CD40. However, the underlying mechanisms by which BCR signals synergize with Toll-like receptor (TLR) signaling in human B cells remain unclear. OBJECTIVE: We sought to elucidate a role of spleen tyrosine kinase (Syk), a key molecule of BCR signaling, in TLR-mediated activation of human B cells. METHODS: Human naive and memory B cells were stimulated with combinations of anti-BCR, soluble CD40 ligand, and CpG. Effects of the Syk inhibitors on several B-cell functions and expression of TLR9, TNF receptor-associated factors (TRAFs), and phospho-nuclear factor κB in B cells were assessed. RESULTS: Activation of BCR synergized with CD40- and TLR9-mediated signals in driving robust proliferation, cell-cycle progression, expression of costimulatory molecules, cytokine production, and immunoglobulin production of human B-cell subsets, especially memory B cells. However, the Syk inhibitors remarkably abrogated these B-cell functions. Notably, after stimulation through all 3 receptors, B-cell subsets induced marked expression of TLR9, TRAF6, and phospho-nuclear factor κB, which was again significantly abrogated by the Syk inhibitors. CONCLUSION: Syk-mediated BCR signaling is a prerequisite for optimal induction of TLR9 and TRAF6, allowing efficient propagation of TLR9-mediated signaling in memory B cells. These results also underscore the role of Syk in aberrant B-cell activation in patients with autoimmune diseases.

[Abnormal expression of chemokine receptor on B cells in patients with SLE].

SLE is a systemic autoimmune disease characterized by overactivation of autoreactive memory B cells. However, little is known about the mechanism of qualitative abnormality of B cells. The subset classification of T cells by expression pattern of master transcription factors and chemokine receptors has been established. The biology of T cells is useful information to assess qualitative abnormality of B cells. Therefore, we focused on the expression of chemokine receptors such as CXCR5 and CXCR3 on B cells in order to define the B cell subset classification in patients with SLE. Our results revealed that pathological B cells, which lose CXCR5 and express CXCR3, might be involved in autoantibody production through the interaction with Tfh cells, and in acquisition of effector function of memory B cells during the pathological process in SLE. In addition, the results revealed that those effector B cells still remained after improvement of disease activity by immunosuppressive therapy, indicating that the quantitative abnormality, which is not improved by current therapy, may underlie in this disease.

Activation of Syk in peripheral blood B cells in patients with rheumatoid arthritis: a potential target for abatacept therapy.

OBJECTIVE: B cells play a pivotal role in the pathogenesis of autoimmune diseases. Although Syk functions as a key molecule in B cell receptor signaling, the pathologic role of Syk in B cells in rheumatoid arthritis (RA) remains unclear. The purpose of this study was to assess the relevance of activation of Syk in B cells to the pathologic development of RA and to the responsiveness of RA patients to treatment with biologics. METHODS: Healthy subjects (n = 36) and patients with moderate or severe RA disease activity (n = 70) were studied. The phosphorylation of Syk (pSyk) in peripheral blood B cells was measured by flow cytometry, and its correlation with clinical characteristics and changes after administration of biologic agents was evaluated. RESULTS: Levels of pSyk in peripheral blood B cells were preferentially higher in patients with RA compared to healthy subjects. Patients with significantly higher pSyk levels were strongly positive for anti-citrullinated protein antibodies (ACPAs). High pSyk levels were not correlated with the severity of disease activity. Treatment with abatacept, but not tumor necrosis factor inhibitors, significantly reduced the levels of pSyk in RA peripheral blood B cells. Abatacept also significantly reduced the proportion of follicular helper T (Tfh) cells. CONCLUSION: Levels of pSyk in peripheral blood B cells were significantly elevated in patients with RA, and these patients also exhibited strong positivity for ACPAs. These data suggest that abatacept seems to inhibit the phosphorylation of Syk in B cells, as well as the development of Tfh cells, thus highlighting the relevance of B cell-T cell interactions as a potential target of abatacept therapy in RA.

[Involvement of Syk in pathology of systemic autoimmune disease].

Biological products have proven its high efficacy on autoimmune disease such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Meanwhile, small molecular drugs have attracted attention over the years because of its availability of oral administration and cost effectiveness. Spleen tyrosine kinase (Syk) is a 72 kDa protein tyrosine kinase widely expressed on cells that are involved in the immune system and inflammation such as B cells, T cells, macrophages and synovial fibroblast. Syk is involved in intracellular signaling of the multi-chain immune receptors, including B cell receptor (BCR), ζchain of T-cell receptor (TCR), FcR and integrins, which contains the immune-receptor tyrosine-based activation motif (ITAM). Recently, Syk inhibitor fostamatinib has exerted potent therapeutic efficacy against autoimmune and allergic diseases such as rheumatoid arthritis (RA), bronchial asthma and thrombocytopenic purpura (ITP). Moreover, Syk blockade prevented the development of skin and kidney lesions in lupus-prone mice, however the mechanism of action is unclear. We have revealed that Syk-mediated BCR-signaling is prerequisite for optimal induction of toll-like receptor (TLR)-9, thereby allowing efficient propagation of CD40- and TLR9- signaling in human B cells. These results indicate that inhibition of Syk have a potential to regulate B-cell mediated inflammatory diseases such as SLE. We here document the in vitro and in vivo effects of a Syk inhibitor for the treatment of autoimmune diseases, mainly in RA and SLE.