Intraglomerular C3 synthesis in human kidney detected by in situ hybridization

Complements 3 and 4 are known to be synthesized in diseased renal tissue and the mRNA of these complements has been demonstrated, using polymerase chain reaction, in renal biopsies from nephritic patients. However, the types of cells producing the complements in intact renal tissue have not been defined. To identify the renal cellular components involved in complement synthesis, we analyzed the expression of C3 mRNA in renal tissues from patients with immune-complex glomerulonephritis by a high-resolution in situ hybridization using digoxigenin-labeled oligonucleotide. Renal tissues from 15 patients with immunoglobulin (Ig) A nephropathy (IgAN), five with lupus nephritis (LN), and five with minimal change nephrotic syndrome (MCNS) were examined. Uninvolved portions of surgically removed kidney with tumors served as normal controls. C3 mRNA was detected in mesangial cells, glomerular epithelial cells, and Bowman's capsule in IgAN and LN. In the interstitium, some tubules and some infiltrating mononuclear cells were positively stained for C3 mRNA. C3 mRNA was not detected in MCNS and control tissues. Our results confirm that the glomerular resident cells can synthesize C3 in immune-mediated glomerulonephritis and suggest that locally synthesized complement may be involved in tissue injury in glomerulonephritis.