Plasma cell and regulatory B Cell-infiltration in the lungs of Bleomycin-treated mice

Introduction STAT3 and B cells are implicated in the development of lung fibrosis. We have previously demonstrated that hyper-activated STAT3, B cell-deficient gp130757F;μMT-/- mice are protected from bleomycin (BLM)-induced lung fibrosis suggesting that B cells are important in the regulation of STAT3-mediated fibrosis. Hypothesis We hypothesise that the pro-fibrotic effects of STAT3 involve B cell-mediated immune regulation. Methods The effect of anti-CD20 therapy in bleomycin-treated wildtype and gp130757F mice on lung fibrosis and immune cell composition was examined. Mice were given two 100μg doses of anti-CD20 antibody (Genentech Inc USA) or IgG2a isotype control i.p. either 7 days prior to and 7 days after bleomycin or on day 10 and day 19 post-bleomycin treatment (following the initiation of fibrosis), and the extent of fibrosis measured at 28 days. Results FACS analysis of blood taken on days 0, 7 and 28 days post-bleomycin-treatment revealed an almost complete depletion of CD19+ B cells in the circulation of wildtype mice but not gp130757F. However, the extent of fibrosis, assessed using micro-CT imaging and HPLC analysis of hydroxyproline levels was not significantly different between treatment groups. Histological analysis revealed an abundance of CD5+ B cells and CD138+ (plasma cells) in the lungs of the anti-CD20-treated mice. FACS analysis identified an expansion of CD138+ (days 7 and 28) and CD5+ cells in the lungs of bleomycin treated mice at day 28. Conclusion Although antibody depletion of follicular B cells had no effect on bleomycin-induced fibrosis, residual CD138+ plasma cells and CD5+ B are abundant in the lungs of bleomycin-treated mice. The activity of these B cell subsets may contribute to the fibrotic phenotype. Grant Support: This work is funded by NHMRC Project Grant GNT1067511 and British Lung Foundation Grant PPRG15-10