Antibacterial precipitating antibodies in Group A hemolytic streptococcus sore throat

1.1. Purified c carbohydrate and a nontype-specific “x” substance present in acid extracts of Group A hemolytic streptococcal cells have been used in precipitin tests with human sera. 2.2. Antibodies against one or the other or both of these antigens were demonstrable in the sera of certain cases of acute streptococcal sore throat at the onset of infection. 3.3. An anti-c antibody response occurred in 6 per cent of the patients, and an anti-x antibody response occurred in 22 per cent of the men infected by Group A hemolytic streptococci. 4.4. The presence or development of neither antibody could be correlated with any aspect of the acute suppurative phase of the illness. 5.5. Poststreptococcal arthritis and pneumonitis occurred more frequently in infected men in whom anti-x antibody was demonstrable in the initial serum or during convalescence than in those in whom it was not present. A similar relationship was not discovered for anti-c precipitin. 6.6. Anti-x antibody was infrequently discovered during the course of streptococcal respiratory disease complicated by late fever. 7.7. It is suggested that the “x” substance may be the antigen responsible for serious streptococcal hypersensitivity.