RESUMO

OBJECTIVE: To determine the immune responses to the streptococcal M protein in patients with poststreptococcal acute glomerulonephritis (PSAGN). STUDY DESIGN: The gene coding type 12 M protein of group A streptococcus (M12), a known PSAGN-associated serotype, was cloned and expressed in Escherichia coli to investigate the specific immune responses to the M12 protein in patients with PSAGN. Recombinant M proteins for the variable N-terminal half (AB region) and conserved C-terminal half (C region) were produced separately. IgG titers against each region were measured by enzyme-linked immunosorbent assay in patients with PSAGN (n = 51), uncomplicated streptococcal pharyngitis (n = 26), chronic glomerulonephritis (n = 10), and in healthy control subjects (n = 51). Immunodominant domains within the M protein in PSAGN were further investigated by use of overlapping synthetic peptides. RESULTS: IgG titers against the C region, but not the AB region, were markedly higher in the PSAGN group than in other groups (p < 0.01), and these titers were maintained for at least several months after antistreptolysin O or antistreptokinase levels had returned to normal. Studies with overlapping synthetic peptides demonstrated that increased IgG reactivity was observed against the C repeat blocks. CONCLUSION: IgG titers against the C region are significantly elevated in patients with PSAGN, and it may be a diagnostic marker for PSAGN.

Assuntos

Anticorpos Antibacterianos/análise , Antígenos de Bactérias/imunologia , Antígenos de Superfície/imunologia , Proteínas da Membrana Bacteriana Externa , Proteínas de Bactérias/imunologia , Proteínas de Transporte , Glomerulonefrite/microbiologia , Imunoglobulina G/análise , Infecções Estreptocócicas/imunologia , Streptococcus pyogenes/imunologia , Doença Aguda , Antígenos de Bactérias/genética , Antígenos de Superfície/genética , Antiestreptolisina/análise , Proteínas de Bactérias/genética , Biomarcadores/análise , Estudos de Casos e Controles , Criança , Doença Crônica , Ensaio de Imunoadsorção Enzimática , Escherichia coli/genética , Feminino , Expressão Gênica , Glomerulonefrite/imunologia , Humanos , Epitopos Imunodominantes/genética , Epitopos Imunodominantes/imunologia , Masculino , Peptídeos , Faringite/imunologia , Faringite/microbiologia , Reação em Cadeia da Polimerase , Proteínas Recombinantes , Sequências Repetitivas de Ácido Nucleico , Análise de Sequência de DNA , Streptococcus pyogenes/genética , Estreptoquinase/análise