Immune response to group A streptococcal C5a peptidase in children: implications for vaccine development.

The group A streptococcal C5a peptidase (SCPA) is a major surface virulence protein that facilitates the establishment of local infection by group A streptococci (GAS). We measured the human immune response to SCPA, using a standardized indirect enzyme-linked immunosorbent assay. Paired acute and convalescent serum samples from children with GAS-associated pharyngitis were assayed, and a strong immune response to SCPA was demonstrated that was independent of the infecting M type and the age of the patient. Western blot analysis of bacterial extracts revealed that all tested M types expressed SCPA. The immune response to SCPA correlated with the anti-streptolysin O and anti-DNase B responses. These data confirm the immunogenicity of SCPA in humans. Previous knowledge of SPCA's role in virulence, its highly conserved nature, and the results of mouse protection studies make SCPA an ideal vaccine candidate for the prevention of GAS disease.