Type-specific opsonophagocytosis of group A streptococcus by use of a rapid chemiluminescence assay

A whole-blood chemiluminescence (CL) assay was developed to determine the p resence of type-specific opsonic antibodies against group A streptococcus ( GAS). Convalescent sera with high bactericidal activities against an M-1 se rotype were used to opsonize different M-types of GAS. CL responses were mo nitored for 20 min, and results were expressed as integral counts/minute pe r phagocyte. CL responses of phagocytes incubated with M-1 GAS opsonized wi th homologous (M-1) serum were significantly higher than responses of phago cytes incubated with heterologous (M-3) GAS. Adsorption of convalescent ser um against the homologous, but not the heterologous, strain markedly reduce d the CL response, demonstrating type specificity. The CL assay showed a hi gh correlation with the indirect bactericidal test (r = 0.90). In conclusio n this CL assay is a rapid, highly sensitive, specific, and reproducible me thod for quantifying type-specific opsonic antibodies against GAS and will be a useful tool for future clinical, basic science, and epidemiological st udies.