Effect of Pseudomonas aeruginosa proteases on human leukocyte phagocytosis and bactericidal activity

The effect of Pseudomonas aeruginosa alkaline protease (AP) and elastase (Ela) on neutrophil phagocytosis and bactericidal activity was examined. It was found that both proteases reduced the phagocytic activity of the leukocytes against P. aeruginosa, whereas they had little effect on the phagocytosis of S. aureus. AP and Ela at concentration of up to 250 micrograms per ml (much higher than the levels detectable under in vivo conditions) did not interfere with the bactericidal activity of the leukocytes against both test organisms. Inhibition of phagocytosis by AP and Ela without effect on the bactericidal activity suggests that the P. aeruginosa proteases most probably exert their effect on the cell surface perhaps by proteolytic cleavage of the cell receptors which are necessary for phagocytosis.