B lymphocytes: shedding new light on the pathogenesis of systemic sclerosis.

Systemic sclerosis (SSc) is a connective tissue disease characterized by autoimmunity and tissue fibrosis. In patients with SSc, there is a close association between the presence of specific autoantibodies and the development of clinical features. Although it is known that cytokines, including transforming growth factor-beta, can modulate the synthesis of extracellular matrix by fibroblasts, it is not clear how autoimmunity and tissue fibrosis are interrelated. Several recent lines of evidence indicate a potential role for B cells in the development of SSc. CD19 is a critical regulator of B-cell signaling thresholds, and B cells from SSc patients exhibit increased expression of CD19, a molecule that induces SSc-specific autoantibody production in transgenic mice. Both SSc patients and tight-skin mice, a genetic model of SSc, have intrinsic B-cell abnormalities characterized by chronic B-cell activation. Remarkably, CD19 loss or B-cell depletion using antimouse CD20 antibody suppresses the development of skin hyperplasia and autoimmunity in tight-skin mice. Additionally, a recent study revealed a possible beneficial effect of antihuman CD20 antibody (rituximab) therapy for SSc patients. As B cells have a variety of functions, further investigation into the pathogenic roles of B cells, as well as trials of B-cell-targeting therapies, may shed new light on the pathogenesis of SSc.