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

Abstract

A whole-blood chemiluminescence (CL) assay was developed to determine the presence of type-specific opsonic antibodies against group A streptococcus (GAS). Convalescent sera with high bactericidal activities against an M-1 serotype were used to opsonize different M-types of GAS. CL responses were monitored for 20 min, and results were expressed as integral counts/minute per phagocyte. CL responses of phagocytes incubated with M-1 GAS opsonized with homologous (M-1) serum were significantly higher than responses of phagocytes incubated with heterologous (M-3) GAS. Adsorption of convalescent serum against the homologous, but not the heterologous, strain markedly reduced the CL response, demonstrating type specificity. The CL assay showed a high correlation with the indirect bactericidal test (r=0.90). In conclusion, this CL assay is a rapid, highly sensitive, specific, and reproducible method for quantifying type-specific opsonic antibodies against GAS and will be a useful tool for future clinical, basic science, and epidemiological studies.