Noncanonical immunomodulatory activity of complement regulator C4BP(β-) limits the development of lupus nephritis

Lupus nephritis is a chronic autoimmune-inflammatory condition that can lead to end-stage kidney disease. Presently available immunosuppressive treatments for lupus nephritis are suboptimal and can induce significant side effects. Recently, we characterized a novel immunomodulatory activity of the minor isoform of the classical pathway complement inhibitor, C4BP(β-). We show here that C4BP(β-) treatment prevented the development of proteinuria and albuminuria, decreased significantly the formation of anti-dsDNA antibodies and, locally, mitigated renal glomerular IgG and C3 deposition and generation of apoptotic cells. There was a consequent histological improvement and increased survival in lupus-prone mice. The therapeutic efficacy of C4BP(β-) was analogous to that of the broad-acting immunosuppressant cyclophosphamide. Remarkably, a comparative transcriptional profiling analysis revealed that the kidney gene expression signature resulting from C4BP(β-) treatment turned out to be 10 times smaller than that induced by cyclophosphamide treatment. C4BP(β-) immunomodulation induced significant downregulation of transcripts relevant to lupus nephritis indicating immunopathogenic cell infiltration, including activated T cells (Lat), B cells (Cd19, Ms4a1, Tnfrsf13c), inflammatory phagocytes (Irf7) and neutrophils (Prtn3, S100a8, S100a9). Furthermore, cytokine profiling and immunohistochemistry confirmed that C4BP(β-), through systemic and local CXCL13 downregulation, was able to prevent ectopic lymphoid structures neogenesis in aged mice with lupus nephritis. Thus, due to its anti-inflammatory and immunomodulatory activities and high specificity, C4BP(β-) could be considered for further clinical development in patients with systemic lupus erythematosus.