Binding of IgA1 and surface-expressed collagen-binding protein of Streptococcus mutans contributes to IgA nephropathy pathogenesis.

BACKGROUND: The present study was conducted to examine the interaction between collagen-binding protein (Cnm) of Streptococcus mutans and immunoglobulin (IgA) to clarify the possible involvement in IgA nephropathy (IgAN) development. METHODS: The binding of Cnm to human immunoglobulins was examined using an enzyme-linked immunosorbent assay. A nephritis-induced rat model was employed to confirm the localization of Cnm. RESULTS: IgA1 showed significantly greater binding ability to Cnm than to other bacterial surface proteins, and Cnm showed significantly greater binding ability to IgA1 than to other immunoglobulins. In rats administered Cnm, IgA deposition was observed in the glomerular mesangial region. Furthermore, biotin-labeled Cnm was observed in the same region as IgA deposition in the Cnm group. CONCLUSIONS: Taken together, it is considered that following invasion into the bloodstream, Cnm binds to and forms a complex with IgA1, leading to deposition of IgA1 in renal glomeruli.