Foxp3+ regulatory T cells control humoral autoimmunity by suppressing the development of long-lived plasma cells.

Foxp3(+) regulatory T cells (Tregs) are crucial for maintaining T cell tolerance, but their role in humoral autoimmunity remains unclear. To address this, we combined a model of autoantibody-dependent arthritis (K/BxN) with Foxp3 mutant scurfy mice to generate Treg-deficient K/BxN mice, referred to as K/BxNsf mice. The disease symptoms of K/BxNsf mice were exacerbated, and this coincided with increases in extrafollicular Th cells, follicular Th cells, and germinal centers. Surprisingly, the K/BxNsf mice exhibited an abnormal accumulation of mature plasma cells in their spleens and a corresponding loss of bone marrow plasma cells. The plasma cells were unresponsive to the bone marrow homing chemokine CXCL12, despite normal expression of the chemokine receptor CXCR4. Importantly, they were long-lived and less susceptible to the cytotoxic action of cyclophosphamide. They also expressed less FcγRIIb and were less apoptotic in response to autoantigen-autoantibody immune complexes. This suggests that Tregs control plasma cell susceptibility to cell death induced by engagement of FcγRIIb with immune complexes. Direct cytotoxic effects of Tregs also contribute to the death of plasma cells. Thus, our results reveal that Tregs suppress the emergence of long-lived splenic plasma cells by affecting plasma cell-autonomous mechanisms as well as T cell help, thereby avoiding the persistence of humoral autoimmunity.

CD4+CD25+ regulatory T cells selectively diminish systemic autoreactivity in arthritic K/BxN mice.

Although the arthritis symptoms observed in the K/BxN model have been shown to be dependent on the functions of T and B cells specific to the self antigen glucose-6-phosphate isomerase, less is known about the in vivo roles of CD4(+)CD25(+) regulatory T (T(reg)) cells in the pathology of K/BxN mice. We determined the quantitative and functional characteristics of the T(reg) cells in K/BxN mice. These mice contained a higher percentage of Foxp3(+) T(reg) cells among the CD4(+) T cells than their BxN littermates. These T(reg) cells were anergic and efficiently suppressed the proliferation of naïve CD4(+) T cells and cytokine production by effector CD4(+) T cells in vitro. Antibody-mediated depletion of CD25(+) cells caused K/BxN mice to develop multi-organ inflammation and autoantibody production, while the symptoms of arthritis were not affected. These results demonstrate that despite the inability of the T(reg) cells to suppress arthritis development, they play a critical role protecting the arthritic mice from systemic expansion of autoimmunity.

Production of Vibrio vulnificus metalloprotease VvpE begins during the early growth phase: usefulness of gelatin-zymography.

Recent studies have demonstrated that expression of the vvpE gene begins during the early growth phase albeit at low levels. However, we found that the traditional protease assay method that is used to measure caseinolytic activity in culture supernatants is not suitable for the measurement of extracellular VvpE that is produced at low levels during the early growth phase. By using gelatin-zymography in place of the protease assay, we could specifically detect only VvpE of several proteases produced by Vibrio vulnificus. Moreover, we could sensitively measure VvpE produced at low levels during the early growth phase, which was consistent with transcription of the vvpE gene. The extracellular production of VvpE was reduced or delayed by mutation of the pilD gene which encodes for the type IV leader peptidase/N-methyltransferase associated with the type II general secretion system; the delayed production of VvpE was recovered by in trans complementation of the wild-type pilD gene. These results indicate that VvpE begins to be produced during the early growth phase via the PilD-mediated type II general secretion system, and that the use of gelatin-zymography is recommended as a simple method for the sensitive and specific detection of VvpE production.

Essential roles of Toll-like receptor-4 signaling in arthritis induced by type II collagen antibody and LPS.

Although bacterial LPS has been used to boost the susceptibility to antibody-induced arthritis, the mechanism of the action of LPS remains to be clarified. We investigated whether signals triggered by Toll-like receptor (TLR)-4 mediate the effects of LPS in the context of anti-type II collagen-induced arthritis. The mice defective in the Tlr-4 gene (Tlr-4(lps-d)) were markedly less susceptible than wild type to arthritis, as manifested in arthritic index, incidence and synovitis. Levels of the pro-inflammatory mediators, tumor necrosis factor-alpha and cyclooxygenase-2, in their synovial tissue were also much lower. Serum C3 deposition through the alternative pathway and de novo synthesis of C3 were lower in the Tlr-4(lps-d) mice in the post-acute phase, pointing to an influence of TLR-4 signals on the turnover rate of complement cascades. T cells from the Tlr-4(lps-d) mice failed to proliferate in response to an auto-antigen, glucose-6-phosphate isomerase (GPI), unlike those from wild-type mice, and the serum level of GPI-specific IgG antibody was significantly lower than in the wild-type mice. Interestingly, type 2 responses, such as GPI-specific IgG1 and IL-4 production, were up-regulated in the Tlr-4(lps-d) mice. Taken together, our data suggest that the TLR-4 signaling pathway plays an essential role in the initiation and progression of auto-antibody/LPS-triggered arthritis by inducing pro-inflammatory mediators, C3 deposition, auto-antigen-specific adaptive immune responses and immune deviation between type 1 and type 2 responses.