Detection of group B streptococcal antibodies in human sera by radioimmunoassay: concentrations of type-specific antibodies in sera of adults and infants infected with group B streptococci

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Abstract
Current interest in determining the possible protective role of antibodies against group B streptococcal disease prompted this study of the feasibility of using a radioimmunoassay to measure type-specific immunity in humans. The radioimmunoassay was standardized as a quantitative test for antibodies against the carbohydrate (CHO) antigens of all 5 group B types. The CHO antigens extracted by a cold trichloroacetic acid-sonification method measure more antibodies than do the corresponding CHO antigens extracted by hot hydrochloric acid. The Ia CHO extracted from 2 different types, Ia and Ic, measure the same quantity of Ia antibodies; and that human sera contain antibodies reactive with all five type-specific CHO. No evidence of protective antibody was found in the serum samples studied, although there was evidence of an antibody response in adults to prolonged colonization by group B streptococci. The wide ranges of antibody concentration in a serum bank collection, the broad reactivity of all human sera tested, and the mixed populations of antibodies in human sera that react with different determinants on the same type-specific CHO antigen (type III) indicate that further studies must be done to better define normal and susceptible populations and to determine antigenic components important in protection.