Human Immunity to Pseudomonas aeruginosa. I. In-Vitro Interaction of Bacteria, Polymorphonuclear Leukocytes, and Serum Factors

Abstract

The interaction between Pseudomonas aeruginosa, human polymorphonuclear leukocytes (PMNs), and serum factors was evaluated by use of serum bactericidal tests and quantitative tests of phagocytosis and killing. Forty-two of 46 blood-culture isolates (91 %) of P. aeruginosa were serum-resistant; organisms recovered from 12 patients who survived bacteremia were not killed by fresh autologous convalescent serum containing high titers of antibody. However, fresh sera from these patients (as well as fresh normal sera), when combined with normal PMNs, promoted a 10- to 100-fold killing of bacteria within 60–120 min. Optimal phagocytosis by PMNs required the presence of heat-stable antibody and heat-labile opsonin; the activity of the latter was primarily due to the first four components of complement. Heat-stable opsonizing antibody was greatly augmented in sera of survivors of bacteremic infection. Normally functioning PMNs are essential to host defenses, since most invasive strains of P. aeruginosa are resistant to serum.