Direct immunofluorescence in cases of postinfectious glomerulonephritis shows granular fluorescence of the glomerular immune complexes in a starry-sky pattern. The fluorescent granules seem randomly scattered throughout the glomerular tuft showing neither a capillary loop pattern nor a clustered mesangial pattern. The immune complexes are presumed to form in situ in the glomeruli due to previously planted streptococcal antigen. Immune complexes form in situ in glomeruli due to previously planted streptococcal antigens.
Most cases are in the pediatric age group.
Streptococcal infections are the most common, but other infectious agents are capable of producing the disease. The kidneys in postinfectious glomerulonephritis may show no particular gross abnormalities. In severe cases, the cut surface of the renal cortex may show a petechial or flea-bitten appearance. The glomeruli are diffusely and globally hypercellular with a predominance of neutrophils. The increased cellularity is endocapillary, meaning that the increase in cells is within the glomerular tuft and there is little if any proliferation of cells in the urinary space.