Antibodies to streptococcal inhibitor of complement function and M peptides in a post-streptococcal glomerulonephritis endemic region of Australia.

Post-streptococcal glomerulonephritis (PSGN) is an immune-mediated disease in which an immune complex containing a streptococcal antigen are deposited in affected glomeruli. Strains of only some M types are known to be associated with PSGN. A secretory protein called SIC inhibits complement function. Whereas all M1 and M57 strains express closely related SIC (CRS), all M12 and M55 strains express distantly related SIC (DRS) proteins. Strains belonging to these four M types are historically associated with PSGN. This study used ELISA to analyse 112 sera from individuals with a recorded history of PSGN and 86 sera from individuals who had no such recorded history, all from a PSGN endemic region in tropical Australia. Antibody reactions to CRS, DRS and peptides corresponding to the N-termini of M1, M5, M12, M49, M55 and M57 antigens were assessed. A large proportion of the population showed reactions to each of these antigens and there was no correlation between CRS seropositivity and antibodies to CRS-positive M types. Likewise there was no correlation between DRS seropositivity and antibodies to DRS-positive M types. Interestingly, in this community endemic for PSGN a significantly higher proportion of DRS seropositive subjects had a recorded history of PSGN than did DRS seronegative subjects. DRS may have a predictive value for PSGN diagnosis or a role in PSGN pathogenesis.