Factors influencing antibody responses to streptococcal M proteins in humans.

In a defined population of 174 children followed at one- to two-week intervals for 23 months, the development of M type-specific antibodies to four different types of group. A streptococci was assayed in 408 serum samples from 68 children who acquired one or more of these types in the upper respiratory tract and/or skin lesions. M type 6, a classic pharyngitis strain, was isolated almost exclusively from the upper respiratory tract. Acquisition of this type resulted in the highest percentage of responders without antibody to M protein and in the greatest magnitude of type-specific bactericidal activity as compared with M types 31, 49, and 52, which were commonly associated with pyoderma lesions. Factors that appeared to influence the M type-specific antibody response included the streptococcal type, the age of the child, the number of culture-positive visits, and the stage of the outbreak. The site(s) of isolation by itself and the serum opacity reaction of the infecting strain did not appear to be important determinants of the M type-specific antibody response.