Hybridoma antibodies against protective and nonprotective antigenic determinants of a structurally defined polypeptide fragment of streptococcal M protein.

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Abstract
Hybridoma technology was used to produce a set of monoclonal antibodies against a purified polypeptide fragment of type 24 streptococcal M protein to delineate the protective determinants of M protein exposed on the surface of the virulent streptococci. Several mouse hybridoma antibodies were found to be opsonic against the homologous type streptococci. At least 2 of these antibodies (IIC3.7 and IIC4.6) protected mice against challenge infections with the homologous, but not a heterologous, serotype of bacteria. One of the hybridoma antibodies that reacted in high dilution (1:204,800) with the isolated M protein failed to react with the M protein on the surface of type 24 streptococci and thus did not opsonize the homologous organisms or protect mice against challenge infections. Because hybridoma antibodies are directed against a single distinct immunodeterminant, protective immunity may be directed at any 1 of several distinct antigenic determinants of M protein exposed on the surface of virulent group A streptococci.