Complete B Cell Deficiency Reduces Allograft Inflammation and Intragraft Macrophages in a Rat Kidney Transplant Model

Background Increasingly, it is being appreciated that B cells have broad roles beyond the humoral response and are able to contribute to and regulate inflammation. The specific role of B cells in the pathogenesis of early allograft inflammation remains unclear. Methods To address this question, we generated B cell–deficient (B−/−) Lewis rats via clustered regularly interspaced short palindromic repeats (CRISPR) technology. In a full mismatch transplant model, kidneys from Brown Norway donors were transplanted into B−/− Lewis recipients or wild type Lewis recipients. T cell–mediated rejection was attenuated with cyclosporine. Results Renal inflammation was reduced at 1 week after transplant (Banff scores for interstitial inflammation, microvascular inflammation, glomerulitis, and C4d) in allografts from B−/− recipients. The reduction in interstitial inflammation was predominantly due to a decline in graft infiltrating macrophages. Intragraft T-cell numbers remained unchanged. In addition, B-cell deficiency was associated with increased T regulatory cells and reduced splenic T follicular helper cells at baseline; and significantly increased intragraft and splenic IL-10 mRNA levels after transplant. In vitro, B−/− and wild type splenic T cells produced similar levels of IFN-&ggr; in response to T cell–specific activation. Conclusions B-cell deficiency in this model produced an anti-inflammatory phenotype with a shift toward regulatory T-cell populations, production of anti-inflammatory cytokines (IL-10), and a reduction in allograft inflammation. These findings define a role for B cells to influence the cell populations and mediators involved in the pathogenesis of early allograft inflammation.