Human immune response to streptococcal C5a peptidase in Indian children and adults

Streptococcal C5a peptidase (SCPA) is a cell bound protease associated with virulence of group A streptococci (GAS). In India, as the incidence of GAS infections and their late sequelae like rheumatic fever (RF), rheumatic heart disease (RHD) and acute glomerulo nephritis (AGN) is very high, it is necessary to characterize the immune response to SCPA. SCPA is considered as a standard vaccine candidate, as anti-SCPA antibodies can neutralize the activity of this enzyme in vitro and in vivo. In the present study, the anti-SCPA IgG levels and their subtypes were determined in 199 serum samples collected from RF/RHD/AGN/NORMAL subjects and the results were correlated with the anti-streptolysin O (ASO) titres. The mean anti-SCPA IgG in normal healthy subjects was 7.35 μg/ml. The level of these antibodies in RF, RHD and AGN cases was found to be 17.58 μg/ml, 12.74 μg/ml and 11.1 μg/ml, respectively. The rise of anti-SCPA IgG observed in patients was irrespective of different emm types of GAS strains isolated from these patients. The findings are helpful for generating base line data of anti-SCPA IgG levels.