BACTERIAL EVASION OF THE ANTIBODY-RESPONSE - HUMAN-IGG ANTIBODIES NEUTRALIZE SOLUBLE BUT NOT BACTERIA-ASSOCIATED GROUP-B STREPTOCOCCAL C5A-ASE

Most strains of group B streptococci (GBS) possess an enzyme that inactivates the human anaphylatoxin C5a by cleaving a heptapeptide from the carboxyl terminus of C5a. This enzyme, called GBS C5a-ase, has been purified to homogeneity and cleaves and inactivates C5a in physiologic buffer. The enzymatic activity of soluble C5a-ase is completely inhibited, however, in the presence of plasma or serum from normal human adults. The neutralization of soluble C5a-ase by plasma and serum results largely from naturally occurring IgG antibodies directed against C5a-ase. IgG does not neutralize C5a-ase present on intact encapsulated type III GBS but does neutralize the C5a-ase activity associated with a transposon-induced mutant strain of type III GBS that lacks capsule. The location of GBS C5a-ase on the surface of encapsulated type III GBS permits the C5a-ase to inactivate C5a while evading neutralization by IgG antibodies.