Involvement of locomotion of granulocytes in the phagocytosis of glass-adherent group B streptococci in the absence of opsonins

Abstract

Phagocytosis of glass-adherent group B streptococci (GBS) by bovine polymorphonuclear leukocytes (PMN) was investigated by a fluorochrome microassay. Three out of the four tested strains were taken up in the absence of serum, but phagocytosis was increased when immobilized bacteria were pre-treated by either normal bovine serum (NBS, containing antibodies to GBS), precolostral calf serum (PCS, virtually devoid of antibodies), heat-inactivated PCS (H-PCS), or to a lesser extent by human serumalbumin (HSA) or gelatin. The fourth strain required opsonization by NBS to be ingested. The under-agarose PMN migration assay showed that HSA, PCS, H-PCS, and NBS had locomotion-promoting effects that ranked as for enhancement of phagocytosis. In addition, fixed antigen-antibody complexes inhibited both migration under agarose and surface phagocytosis. These findings suggested that when bacteria are sensitive to surface phagocytosis in the absence of opsonins, the enhancing effect of serum is essentially mediated through promotion of PMN locomotion and not through opsonin-enhanced ingestion.