Phagocytosis by Human Leucocytes. I. Effect of Fibrin on Phagocytosis of Staphylococci and of Encapsulated Pneumococci by Normal Human Leucocytes1

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Abstract
Fibrin formed in blood as a result of coagulase production by staphylococci appears to diminish the ingestion of the microorganisms by human neutrophilic polymorphonuclear leucocytes. The in vitro inhibition was not of sufficient magnitude to indicate that coagulase is of prime importance in staphylococcal pathogenicity. Using a newly described technique, a quantitative evaluation of "surface phagocytosis" of encapsulated pneumococci was obtained. Exposure of type II encapsulated pneumococci to neutrophils in a fibrin clot resulted in a marked increase in the mean ingestion of the microorganisms over that occurring in a fluid medium. The observed ingestion was nearly as efficient as opsonin-potentiated phagocytosis. The addition of streptokinase to the in vitro preparations, which prevented fibrin formation, resulted in increased but not a maximal ingestion of coagulase positive staphylococci; but the ingestion of encapsulated pneumococci was significantly reduced in the absence of fibrin.