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Cationic polyamino acids are known to enhance a variety of cell-cell interactions by virtue of their ability to alter electrostatic forces of cell surfaces. In this study, the effect of polyamino acids on phagocytosis of 3H-labeled bacteria by human polymorphonuclear leukocytes (PMNs) and peritoneal macrophages was investigated. Negatively charged and neutral polyamino acids did not influence phagocytosis of unopsonized Staphylococcus epidermidis, whereas protamine, poly-L-arginine, and poly-L-lysine stimulated phagocytosis in a dose-dependent manner. At 50 micrograms/ml, greater than 30% uptake by PMNs was seen with each of these cationic polyamino acids. Although cationic polyamino acids promoted PMN and peritoneal macrophage phagocytosis of unopsonized S. epidermidis, Staphylococcus aureus M (encapsulated) and M variant (unencapsulated), and Escherichia coli J5, little effect was seen with the parent E. coli O111:B4 or a serotype O222:H16 strain. Pretreatment of bacteria and phagocytes separately demonstrated that the phagocytosis-promoting property of polyamino acids is manifest predominantly on the bacteria. Bacteria pretreated with cationic polyamino acids also elicited a PMN chemiluminescent response, and PMN-associated bacteria were killed, as determined by a fluorochrome microassay. Thus, cationic polyamino acids promote the phagocytosis and killing of many but not all bacterial strains, and in this respect polyamino acids function as opsonins.

Polyamino acid enhancement of bacterial phagocytosis by human polymorphonuclear leukocytes and peritoneal macrophages