Phagocytosis of Type III Group B Streptococci by Neonatal Monocytes: Enhancement by Fibronectin and Gammaglobulin

The potential of fibronectin to enhance phagocytosis of type III group B streptococci by cultured neonatal monocytes was evaluated. Fibronectin had significantly less effect on phagocytosis compared with type-specific antibody to group B streptococci; fibronectin increased the cell association of organisms to a level comparable to that of adult pooled serum and significantly more than that of serum-free controls. Microbicidal activity suggested that this cell association consisted of attachment but not ingestion, and electron micrographs showed the extracellular location of these organisms. In contrast, the effect of fibronectin on type III group B streptococci preopsonized with intravenous gammaglobulin revealed significantly greater numbers of cell-associated organisms than did addition of type-specific antibody to group B streptococci, pooled adult serum plus fibronectin, or serum-free controls. Phagocytosis was similar when assessed by microbicidal activity compared with the cultures with added type-specific antibody and significantly greater when compared with those with added pooled serum, and results were confirmed by electron microscopy. Therefore, fibronectin together with intravenous gammaglobulin enhanced ingestion of type III group B streptococci by neonatal monocytes.