TLR7 responses in glomerular macrophages accelerate the progression of glomerulonephritis in NZBWF1 mice

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by the production of autoantibodies and damage to multiple organs. Glomerulonephritis, a manifestation involving glomerular deposition of immune complexes and complement components, significantly contributes to disease morbidity. Although the endosomal single-stranded RNA sensor TLR7 is known to drive glomerulonephritis by promoting autoantibody production in B cells, the contribution of macrophage TLR7 responses to glomerulonephritis remains poorly understood. Here, we have examined Tlr7‒/‒ NZBWF1 mice and found that TLR7-deficiency ameliorates lupus nephritis by abolishing autoantibody production against RNA-associated antigens, C3 deposition, and macrophage accumulation in glomeruli. Furthermore, TLR7 signaling increased CD31 expression on glomerular endothelial cells and Ly6Clow macrophages but not on T and B cells, suggesting that CD31 mediates TLR7-dependent migration of monocyte into glomeruli. Compared to their splenic counterparts, glomerular macrophages produced IL-1β in a TLR7-dependent manner. In addition, single cell RNA sequencing (scRNA-seq) of glomerular macrophages revealed that TLR7 signaling induced expression of lupus associated genes including those encoding Chitinase 3 like 1, ferritin heavy chain 1, IKKε, and complement factor B (CfB). Although serum CfB did not increase in NZBWF1 mice, TLR7-dependent CfB protein expression was detected in glomerular macrophages. In addition, TLR7 signaling promoted C3 cleavage and deposition predominantly on mesangial cells. These findings suggest that TLR7 responses in glomerular macrophages accelerates the progression of glomerulonephritis in NZBWF1 mice.