Antibody response to IgA-binding streptococcal M proteins in children with IgA nephropathy.

BACKGROUND: IgA nephropathy (IgAN), the most common glomerulonephritis worldwide, is characterized by mesangial deposits containing predominantly IgA. IgAN commonly occurs or exacerbates after upper respiratory tract infections such as streptococcal pharyngitis. Certain group A streptococci express M proteins with IgA-binding regions (IgA-BRs). We have previously shown that these IgA-BRs co-localize with mesangial IgA in IgAN. METHODS: Blood samples from patients with IgAN (n = 21) and age-matched controls (n = 83) were assayed by ELISA to detect an IgG antibody response to the IgA-BRs of the M4, M22 and M60 proteins. Antibodies were assayed for each IgA-BR separately and the results were combined. RESULTS: Antibody levels to the IgA-BRs were significantly higher in IgAN patients than controls (P = 0.016), particularly in patients with recent streptococcal infection (P = 0.008). Conclusions. The results suggest that children with IgAN had a previous infection with a streptococcal strain expressing an IgA-binding M protein.