C3 and infection: The clinicopathological features of this case, that is, the development of massive hematuria and hypocomplementemia approximately 14 d after the onset of infection in the lower leg, the glomerular histology of diffuse endocapillary proliferative glomerulonephritis with massive glomerular infiltration of neutrophils, the strong IF staining for C3 along the capillary walls, and the existence of a subepithelial hump, strongly suggest the diagnosis of acute-phase IRGN.