Abstract
BACKGROUND: The mechanisms involved in the pathogenesis of autoimmune disorders, including systemic lupus erythematosus (SLE), have not been fully elucidated. Some of these mechanisms involve epigenetic regulation of gene expression. The histone methyltransferase Ezh2 contributes to epigenetic regulation of gene expression, is highly expressed in germinal center (GC) B cells and follicular T helper (T(FH)) cells, and may be involved in lupus pathogenesis. METHODS: The murine bm12 model of lupus-like chronic graft versus host disease (cGVHD) was induced by intra-peritoneal injection of negatively isolated allogeneic CD4(+) T cells. Lupus-like disease development was monitored by ELISA determination of serum anti-dsDNA and anti-chromatin antibody titers. Immune cell activation and Ezh2 expression were evaluated by flow cytometry and Western blotting. RESULTS: Decreased autoantibody production and GC formation are observed when Ezh2-deficient CD4(+) T cells are used instead of wild-type (WT) to induce cGVHD and when mice that receive allogeneic WT donor T cells to induce cGVHD are treated with GSK503, an Ezh2-specific inhibitor. In the bm12 cGVHD model, WT donor T cells are normally fully activated 1 week after infusion into an allogeneic host, exhibit a T(FH) cell (PD-1(hi)/CXCR5(hi)) phenotype with upregulated Ezh2, and activate B cells to form germinal centers (GCs). In contrast, Ezh2-deficient donor T cells generate fewer T(FH) cells that fail to activate B cells or promote GC formation. Despite similar T-independent, LPS-induced B cell responses, OVA-immunized CD4.Ezh2-KO mice had a skewed low-affinity IgM phenotype in comparison to similarly treated WT mice. In addition, early after OVA immunization, more CD4(+) T cells from B6.CD4.Ezh2-KO mice had a CD44(lo)/CD62L(lo) phenotype, which suggests arrested or delayed activation, than CD4(+) T cells from ovalbumin-immunized B6.WT mice. CONCLUSION: Ezh2 gene deletion or pharmacological Ezh2 inhibition suppresses autoantibody production and GC formation in bm12 lupus-like cGVHD and decreases affinity maturation and isotype switching in response to immunization with a T cell-dependent antigen. Ezh2 inhibition may be useful for the treatment of lupus and other autoimmune disorders.