Factors in normal human serum that promote bacterial phagocytosis.J. Infect. Dis

Heat-stable and heat-labile factors of normal human serum involved in opsono-phagocytosis and intracellular killing of Pseudomonas aeruginosa by human poly-morphonuclear leukocytes were investigated. Specific natural IgG antibodies, properdin, and a heat-labile factor (presumably C3 proactivator) were all re-quired for phagocytosis and bactericidal activity. This finding suggested that an alternate pathway of the complement system was activated. Addition of immune IgG antibodies to the system eliminated the requirement for properdin and the heat-labile factor. Thus, two different mechanisms of complement activation can participate in the opsonophagocytosis of P. aeruginosa. The capacity of normal animals to resist micro-bial infection depends on numerous humoral and cellular factors, which, when acting in concert, provide adequate antimicrobial protection in the absence of acquired specific immunity. Both heat-labile and heat-stable factors in normal serum aid in the ingestion and killing of extracellular micro-organisms by phagocytic cells [1]. The heat-labile factors in normal serum that enhance phagocy-tosis are components of the complement system [2, 3]. The heat-stable natural antibodies of both classes IgG and IgM are present in sera of all normal adult animals and are directed against a wide array of microbial species [4]. It has been well documented that the bacteriolytic activity of normal serum is dependent on the synergistic ac-tion of these antibodies and complement [5, 6]. However, the contribution of these factors to the opsonic activity of normal serum remains contro-versial. In the present study, the factors of normal human serum that promote opsonophagocytosis and intracellular killing of bacteria by human polymorphonuclear leukocytes (PMNs) were in-vestigated. A strain of Pseudomonas aeruginosa was selected for our experiments. This bacterium This study was supported in part by Parke-Davis &amp