The Tetraspanin CD37 Protects Against Glomerular IgA Deposition and Renal Pathology

The tetraspanin protein CD37 is a leukocyte-specific transmembrane protein that is highly expressed on B cells. CD37-deficient (CD37−/−) mice exhibit a 15-fold increased level of immunoglobulin A (IgA) in serum and elevated numbers of IgA+ plasma cells in lymphoid organs. Here, we report that CD37−/− mice spontaneously develop renal pathology with characteristics of human IgA nephropathy. In young naïve CD37−/− mice, mild IgA deposition in glomeruli was observed. However, CD37−/− mice developed high titers of IgA immune complexes in serum during aging, which was associated with increased glomerular IgA deposition. Severe mesangial proliferation, fibrosis, and hyalinosis were apparent in aged CD37−/− mice, whereas albuminuria was mild. To further evaluate the role of CD37 in glomerular disease, we induced anti-glomerular basement membrane (GBM) nephritis in mice. CD37−/− mice developed higher IgA serum levels and glomerular deposits of anti-GBM IgA compared with wild-type mice. Importantly, glomerular macrophage and neutrophil influx was significantly higher in CD37−/− mice during both the heterologous and autologous phase of anti-GBM nephritis. Taken together, tetraspanin CD37 controls the formation of IgA-containing immune complexes and glomerular IgA deposition, which induces influx of inflammatory myeloid cells. Therefore, CD37 may protect against the development of IgA nephropathy.