Lupus serum IgG induces microglia activation through Fc fragment dependent way and modulated by B-cell activating factor.

BACKGROUND: Neuropsychiatric manifestations are frequent in patients with systemic lupus erythematosus (SLE), yet the etiology and pathogenesis of brain damage in SLE remains unclear. Because the production of autoantibodies, formation and deposition of immunocomplexes are major serological characteristics of SLE, the elevated level of serum immunoglobulin may contribute to brain tissue injury of SLE. To testify this, in this study, we examined whether immunoglobulin G (IgG) in the serum of SLE patients affects the cellular functions in central nervous system and the potential mechanism. METHODS: In vivo intracerebral injection of SLE-serum in mouse was used to activate microglia and the production of pro-inflammatory cytokine was assessed by ELISA. Sera was divided into IgG and IgG depleted fractions, while IgG was further divided into Fc and Fab fragments to examine which part has an effect on microglia. Flow cytometry, immunofluorescence and quantitative PCR (qPCR) were used to verify the synergistic effect of B-cell activating factor (BAFF) on IgG stimulation of microglia. RESULTS: We found that IgG in lupus sera can induce M1 activation of brain microglia following intraventricular injection into normal mice, and BAFF facilitates this process. In vitro, we identified that IgG bound to microglia through Fc rather than Fab fragments, and BAFF up-regulated the expression of Fc receptors (FcγR) on the surface of microglia, consequently, promote IgG binding to microglia. CONCLUSION: Our results suggest that lupus serum IgG causes inflammatory responses of microglia by involving the Fc signaling pathway and the activity could be up-regulated by BAFF. Accordingly, disruption of the FcγR-mediated signaling pathway and blockade of microglia activation may be a therapeutic target in patients with neuropsychiatric lupus erythematosus.

Intracerebroventricular administration of lupus serum induces microglia activation and leukocyte adhesion in the cerebromicrovasculature of mice.

BACKGROUND: Central nervous system (CNS) involvement is commonly seen in the patients with system lupus erythematosus (SLE). Mechanisms underlying CNS damage in SLE remain largely unknown. Accumulating evidence suggest that activation of microglia in CNS plays an important role in the inflammatory responses in neurological diseases. The aim of this study is to examine the involvement of microglia in the CNS inflammatory responses induced by circulating serum of SLE patients. METHODS: We performed intracerebroventricular (ICV) injection of serums collected from SLE patients or healthy controls to mice, and examined phenotypic changes of microglia, the levels of cytokines, chemokine and adhesion molecules in the brain. Intravital microscopy was used to observe leukocyte rolling and adhesion in the cerebromicrovasculature. We further examined whether minocycline can block inflammatory responses induced by SLE serum. In vitro experiments were conducted to examine whether IgGs from the sera of SLE patients or healthy control can activate the primary cultured microglia. RESULTS: We found that ICV injection of SLE serum increases morphological activation of microglia in the cortex and hippocampus. Inflammatory mediators including pro-inflammatory cytokines (IL-1, IL-6 and TNF-α), chemokine (CCL2 and CCL5) and adhesion molecules (P-selectin and ICAM-1) were significantly elevated in the brains of SLE-serum-treated mice. Using intravital microscopy, we demonstrated that SLE serum promotes leukocyte rolling and adhesion. Furthermore, suppression of microglia activation by systemically using minocycline could decrease the levels of inflammatory molecular, and prevent leukocyte rolling and adhesion. The in vitro experiments revealed that IgG from SLE sera could be engulfed by microglia and stimulated the microglia to secret pro-inflammatory cytokines. CONCLUSION: Our data suggest that the activation of microglia, which promotes leukocyte adhesion to the brain microvasculature, is an important pathological mechanism of CNS involvement in SLE.

Altered chemokine receptor expression in the peripheral blood lymphocytes in polymyositis and dermatomyositis.

OBJECTIVE: To examine the expression of chemokine receptors in different peripheral blood T-cell subsets in patients with polymyositis (PM) and dermatomyositis (DM). METHODS: We used flow cytometry to measure the frequencies of chemokinereceptors CXCR3 and CCR4 expression in the CD4+ or CD8+ lymphocytes. Enzyme linked immunosorbent assays were also used to measure the concentrations of C-X-C motif chemokine 10 (CXCL10), thymus and activation regulated chemokine (TARC) and macrophage derived chemokine (MDC). RESULTS: Comparing to 20 healthy controls, %CD4+CXCR3+ and %CD8+CXCR3+ T cells significantly decreased in 33DM patients, and %CD8+CXCR3+ cells decreased in 24PM patients, but %CD4+CCR4+ and %CD8+CCR4+ cells did not significantly change in both the PM and DM patients. Accordingly, the Th1/Th2 polarization, analyzed as the balance obtained after dividing %CD4+CXCR3+ cells by %CD4+CCR4+ cells, showed a significant reduction in DM. The serum concentration of CXCR3+ ligand, CXCL10, significantly increased and negatively correlated with circulating %CD4+CXCR3+ cells in DM patients. There was no significant change of TARC and MDC in PM and DM patients. Furthermore, %CD4+CXCR3+ cells decreased more severely in the patients with interstitial lung disease. CONCLUSIONS: The present results indicate that the distributions of circulating CXCR3+ T-cells differ among the PM and DM cases. Our findings suggest a pathogenic difference between PM and DM.