Opsonic Effect of Fibronectin on Staphylococcal Phagocytosis by Human Polymorphonuclear Leukocytes: Its Relative Inefficiency in Post-Phagocytic Metabolic Activities and in Intracellular Killing

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Abstract
The binding of 125I-labeled human plasma fibronectin (FN) to two strains of live Staphylococcus aureus (S. aureus) (a coagulase-positve Cowan I and a coagulase-negative Newman D2C) and the opsonic effect of FN on phagocytosis of these bacteria by human polymorphonuclear leukocytes (PMN) have been studied. 125I-FN bound to a similar extent in both staphylococcal strains. The 125I-FN-binding was significantly inhibited by human fibrinogen as well as unlabeled FN. The FN-binding was also reduced markedly by trypsinization of these bacteria, but the extent of its decrease did not correlate with their tryptic susceptibility of protein A and clumping factor. FN enhanced the uptake of these bacteria by PMN. However, its binding had no effect on superoxide anion (O2-) generation. The FN-binding definitely stimulated staphylococcal ingestion and intracellular killing by PMN, but the extent of such promotion was dissimilar between these two strains of bacteria. These results suggest that post-phagocytic metabolic activities as well as intracellular killing of these Staphylococci may also be greatly influenced by FN-unrelated factors as are other bacteria having no FN-receptors.