The mode of action of antibody in neutrophil bactericidal activity against highly pathogenic group-B streptococci.

An investigation was undertaken into the post-phagocytic action of specific antibody in initiating neutrophil bactericidal activity against highly pathogenic group-B streptococci that survive within these cells. Specific antibody appears to gain access to the interior of the neutrophil and binds to the intracellular bacteria. Activation of Fc receptors on the neutrophil surface is not sufficient to initiate bactericidal activity, but the antibody may utilise the surface Fc receptors to gain access to the ingested organisms. Fusion of the lysosomes with the phagosomes containing the streptococci occurs normally in the cells, and proceeds in both the presence and absence of specific antibody. The organisms are resistant, however, to the microbicidal agents of lysosomes. A significant role is demonstrated for specific antibody in "masking" protective determinants on the bacterial surface during the destruction of these organisms by neutrophils. The relevance of antibody entry into neutrophils in relation to the treatment of bacterial infection is discussed.