A case of superantigen-related glomerulonephritis after methicillin-resistant Staphylococcus aureus (MRSA) infection.

A case in which the enterotoxins of Staphylococcus aureus may have served as bacterial superantigens is presented. This 71-year-old man developed proteinuria and renal dysfunction after contacting pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA), coagulase type II. The infection occurred after surgery for recurrent lung cancer. Staphylococcus enterotoxins B, C, and TSST-1 were detected from the bacillus. Ten days after the onset of pneumonia, proteinuria was noted; urinary protein was as high as 1.8 g/day. The serum creatinine was elevated from 1.0 mg/dl to 3.7 mg/dl. Several immunological reactions were detected; the serum levels of IgG and IgA were increased, and the selective usage of T-cell receptor V beta (TCRV beta) was observed. Serum levels of IL-1 beta, IL-2, IL-6, IL-8, IL-12, and tumor necrosis factor alpha (TNF alpha) were also elevated. Examination of the renal biopsy specimen by light microscopy showed minor to mild mesangial proliferative glomerulonephritis. Immunofluorescence microscopy demonstrated the deposition of IgG, IgA, and C3, mainly along the capillary walls. Electron microscopy revealed electron dense deposits, mainly in the subepithelial areas, and injury to the glomerular basement membrane. When the pneumonia improved following antibiotic therapy, the renal function also improved, and proteinuria decreased. The levels of immunoglobulins and the usage of TCRV beta also decreased. Because staphylococcus enterotoxins act as superantigens, we believe this to be a typical case of superantigen-related glomerulonephritis.