Modulation of phagocytosis and intracellular bactericidal activity of polymorphonuclear and mononuclear cells by cationic proteins from human granulocytes: alternative pathway of phagocytic enhancement.

Cationic lysosomal proteins from human polymorphonuclears (PMN) were isolated by column chromatography and divided into five fractions. On acrylamide gel electrophoresis, fraction I had four bands slower than lysozyme (LZM) mobility; fraction II had five or six bands slower than LZM; fraction III had at least seven bands slower and two bands faster than LZM; fraction IV contained LZM, two bands faster and a few faint bands slower than LZM; fraction V was composed of almost pure LZM. Partial characterization of the fractions showed presence of neutral protease in fractions I-IV, chymotrypsin in fraction III, lysozyme in fractions IV and V, and phospholipase A2 mainly in fractions II and III. Modulatory activity of fractions I-V were tested at concentrations up to 50 micrograms/ml. Enhancement of phagocytosis of Staphylococcus aureus was observed by fractions I, IV, and V, whereas phagocytic index was enhanced by all but the fraction II. Intracellular bactericidal activity (ICBA) was markedly enhanced by fractions I, II, and V. Addition of DNA or cytochalasine B inhibited or abolished phagocytosis-enhancing activity of cationic fractions. Their influence on ICBA was much less pronounced. Fraction III enhanced phagocytic index and phagocytosis of E. coli, whereas fractions I and II enhanced intracellular bactericidal activity against this bacteria. Enhancement of phagocytic activity of monocytes has also been observed. The data suggest that some cationic lysosomal fractions from human PMNs enhance phagocytosis and phagocytic index by human PMNs and monocytes and intracellular bactericidal activity of human PMNs. This alternative pathway of phagocytic enhancement is unrelated to the previously described enhancers of phagocytosis and may play a role in defense mechanisms against infection.