RESUMO
Immunity to group A streptococci (GAS) is thought to be related to the acquisition of type-specific antibody directed against the M protein. However, recent work suggests that immunity may only be strain and not M-type specific. Therefore, susceptibility of 70 different GAS M-1 strains to opsonization and killing by convalescent sera was compared by using a highly sensitive chemiluminescence assay and by standard bactericidal assay. Sequencing of the emm1 gene in 10 strains with variable susceptibility to opsonization revealed 100% homology in 9 strains. Several substitutions in the N-terminal and 2 in the A3 repeat regions of strain CS-190 were associated with profound resistance to opsonization. Thus amino acid substitutions within different regions of the M-1 protein molecule may adversely affect opsonization by immune sera. In addition, non-M protein factors from identical M types influence susceptibility to phagocytosis. These findings may in part explain the persistently high prevalence of M-1 strains worldwide over the last 15 years.
Assuntos
Antígenos de Bactérias , Proteínas da Membrana Bacteriana Externa , Proteínas de Bactérias/imunologia , Proteínas de Transporte/imunologia , Soros Imunes/imunologia , Proteínas Opsonizantes/imunologia , Fagocitose/imunologia , Streptococcus pyogenes/imunologia , Sequência de Aminoácidos , Substituição de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Atividade Bactericida do Sangue , Proteínas de Transporte/química , Proteínas de Transporte/genética , Proteínas do Sistema Complemento/imunologia , Humanos , Medições Luminescentes , Dados de Sequência Molecular , Análise de Sequência de DNA , Sorotipagem , Infecções Estreptocócicas/microbiologia , Streptococcus pyogenes/classificaçãoRESUMO
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.