Macrophages Are Essential Contributors to Kidney Injury in Murine Cryoglobulinemic Membranoproliferative Glomerulonephritis

Mice transgenic for thymic stromal lymphopoietin (TSLP), under regulation of the lymphocyte-specific promoter Lck, develop cryoglobulinemia and membranoproliferative glomerulonephritis (MPGN) similar to the disease in patients. To determine whether infiltrating macrophages, a hallmark of this disease, are deleterious or beneficial in the injury process, we developed Lck-TSLP transgenic mice expressing the human diphtheria toxin receptor (DTR) under control of the monocyte/macrophage-restricted CD11b promoter (Lck-TSLP;CD11b-DTR). Treatment with DT resulted in a marked reduction of monocytes/macrophages in the peritoneal cavity of both CD11b-DTR and Lck-TSLP;CD11b-DTR mice and marked reduction of macrophage infiltration in glomeruli of Lck-TSLP;CD11b-DTR mice. Lck-TSLP;CD11b-DTR mice, with or without toxin treatment, had similar levels of cryoglobulinemia and glomerular immunoglobulin deposition as Lck-TSLP mice. Lck-TSLP;CD11b-DTR mice, treated with toxin, had reduced mesangial matrix expansion, glomerular collagen IV accumulation, expression of the activation marker α-smooth muscle actin and transforming growth factor-β1 in mesangial cells, and proteinuria compared with control mice. Thus, macrophage ablation confers protection in this model and indicates a predominately deleterious role for macrophages in the progression of kidney injury in cryoglobulinemic MPGN.