IMMUNOGLOBULINS TO GROUP-A STREPTOCOCCAL SURFACE MOLECULES DECREASE ADHERENCE TO AND INVASION OF HUMAN PHARYNGEAL CELLS

The M protein is one of the most important virulence factors of group A streptococci (Streptococcus pyogenes) and mag pig an important role in the first steps of streptococcal infection. Since acute pharyngitis is a frequently occurring infectious disease caused by these bacteria , we wished to know whether antibodies to the M protein or other surfa ce components inhibit adherence and internalization of streptococci to pharyngeal cells. We investigated the role of whole human secretary i mmunoglobulin A (sIgA), M6 protein-specific sIgA, and MG protein-speci fic serum IgG in the inhibition of streptococcal adherence and interna lization to cultured human pharyngeal cells. S. pyogenes D471, which p roduces a type 6 M protein (M+), and its isogenic M-negative (M-) deri vative JRS75 were tested. Purified whole sIgA, M protein-specific sIgA , and sIgA preabsorbed with M protein were able to decrease significan tly the adherence of streptococci to pharyngeal cells. Purified IgG ag ainst the M6 protein did not diminish the attachment of streptococci t o the pharyngeal cells but did reduce internalization. Thus, our data suggest that secretory IgA may play a key role in preventing streptoco ccal infection at mucosal surfaces by blocking adherence while affinit y-purified anti-M protein-specific IgG blocks epitopes responsible for invasion.