Background Response Gene to Complement (RGC)-32 is a cell cycle regulator induced by complement activation, growth factors and cytokines. RGC-32 mediates TGF-β dependent profibrotic pathways, while in immune cells promotes the differentiation of Th17 cells. We have previously shown that RGC-32 promotes organ damage in the nephrotoxic nephritis (NTN) mouse model of glomerulonephritis (GN) through proinflammatory and profibrotic pathways. To further define the mechanisms underlying the role of RGC-32 in immune complex GN, we induced NTN in WT and RGC-32-/- mice and assessed local recruitment of IFN-γ and IL-17 producing cells and subsequent renal inflammation.

Methods Proteinuria, blood urea nitrogen and kidney histopathology were determined to assess kidney damage. Single cell suspension of infiltrating kidneys were analyzed by flow cytometry for frequency of IL-17A+, IFN-γ+, FoxP3+ T cells, Ly6g+Ly6c+ neutrophils, CD11b/F4/80lo monocytes and CD11b/F4/80hi macrophages. mRNA expression of IL-17A+, IFN-γ+, FoxP3, CCR6, CCL20, CXCL1, CXCL2, CXCL5, CXCL9, CXCR3 was assessed by RT-PCR

Results Induction of NTN resulted in significantly decreased glomerular damage and proteinuria in RGC- 32-/- NTN mice as compared to WT NTN controls. mRNA expression of IL-17A and CCR6 and the proportion of renal IL-17A+ CD4 cells were significantly decreased. The decrease in IL-17A+ CD4 cells in RGC-32-/- mice was paralleled by decreased mRNA expression of the Th17 ligand, CCL20 in the renal tissue and infiltrating kidney cells. Transcript expression of IL-17 induced chemokines CXCL1, CXCL2, CXCL5 and the subsequent influx of neutrophils were significantly decreased in RGC-32-/- NTN mice. At later timepoints, mRNA expression of IFN-γ, CXCL9 and CXCR3, the frequency and number of renal IFN-γ+ CD4 cells and the influx of monocytes and macrophages were also significantly decreased in RGC-32-/- NTN mice. There was no difference in FOXP3 mRNA transcripts and in the absolute number of renally infiltrated FoxP3 +CD4+ cells between groups. The systemic T cell response assessed by flow cytometry of spleen cells showed comparable frequency of effector CD4+ T cells (CD4+CD62LloCD44hi), Tregs (CD4+CD25+Foxp3+) and IFN-γ and IL-17A expressing CD4+ T cells in WT and RGC-32-/- NTN mice.

Conclusions These data suggest that RGC-32 promotes renal recruitment of Th1 and Th17 cells through CXCL9/CXCR3 and CCL20/CCR6 ligand/receptor interaction and enhances renal damage by promoting the subsequent influx of proinflammatory neutrophils, monocytes and macrophages.