The Human Antibody Response to Streptococcal C5a Peptidase

An ELISA was developed to measure antibody, both IgG and IgA, against the streptococcal CSa peptidase (SCP), in human sera and saliva. Generally, sera and saliva from young, uninfected children lacked antibody to SCPo In contrast, most sera and saliva specimens from healthy adults had measurable levels of anti-SCP IgG and SCP-specific secretory IgA (anti-SCP sIgA). Paired acute and convalescent sera from patients with streptococcal pharyngitis possessed significantly higher levelsof anti-SCP IgG than did sera from healthy individuals. Sera containing high concentrations of anti-SCP immunoglobulin were capable of neutralizing SCP activity. A survey of healthy adults and children also showed that the latter were significantly less likely to have anti-SCP sIgA in their saliva. Detection of this antibody in > 90% of the saliva specimens obtained from children who had recently experienced streptococcal pharyngitis demonstrated that children can produce a secretory response. This is thought to bethe first report of a secretory IgA response in humans to a somatic antigen of Streptococcus pyogenes.