Glomerulonephritis associated with MRSA infection: a possible role of bacterial superantigen.

We report 10 cases of glomerulonephritis following methicillin-resistant Staphylococcus aureus (MRSA) infection. The clinical features of this syndrome were an abrupt or insidious onset of rapidly progressive glomerulonephritis (RPGN) with nephrotic syndrome and occasionally purpura, following MRSA infection. The renal histologic findings showed a variety of types of proliferative glomerulonephritis with varying degrees of crescent formation; immunofluorescence revealed of glomerular deposition of IgA, IgG, and C3. Laboratory findings showed polyclonal increases of serum IgA and IgG, with high levels of circulating immune complexes (ICs). Increased numbers of DR+CD4+, and DR+CD8+T cells were observed in the peripheral circulation, with a high frequency of T cell receptor (TCR) V beta + cells. MRSA produced enterotoxins C and A and toxic shock syndrome toxin (TSST)-1, all of which are known to act as superantigens. From the above observations, we speculate that post-MRSA glomerulonephritis may be induced by superantigens causing production of high levels of cytokines, and polyclonal activation of IgG and IgA. The formation of ICs containing IgA and IgG in the circulation result in development of glomerulonephritis and vasculitis. Accordingly, microbial superantigens may play an important role in the pathogenesis of this unique syndrome of nephritis and vasculitis.