Surface Phagocytosis

Abstract

Experiments recently reported (18) have been interpreted to indicate that surface phagocytosis plays no significant part in natural antipneumococcal defense. A repetition of these experiments has revealed: (a) that the cellular content of the leucocytic suspensions used in the phagocytic tests was of a different order of magnitude from that of the exudates which usually exist in infected tissues, (b) that the suspensions were too dilute to allow surface phagocytosis of pneumococci to occur, and (c) that the ratio of bacteria to leucocytes. was such that, when a sufficiently concentrated exudate was employed, the pneumococci injured the leucocytes and thus prevented phagocytosis from taking place. When conditions of the tests were suitably controlled, and conventional quantitative methods were employed to measure the end results of the phagocytic reaction, the essential observations relating to surface phagocytosis were fully confirmed. The significance of this non-antibody mechanism of defense in pneumococcal infections was thus further substantiated.

Studies on the Pathogenicity of Group a Streptococci

“…Tests for surface phagocytosis were performed as previously described (16)(17)(18). The streptococcus-leucocyte mixture (0.03 ml.)…”

“…Phagocytic Tests in Vitro.--Tests for phagocytosis in vitro were performed on glass slides, in roller tubes (29), and on the surfaces of fresh tissue (16) or moistened filter paper (16)(17)(18). The bacteria were harvested from 2 to 2~ hour cultures, and after having been washed twice in iced Locke's or gelatin-Locke's solution, the centrifugate was diluted in broth and counted in a Petroff-Hausser counting chamber.…”

“…with iced gelatin-Locke's solution. The final suspension, which contained a 1 to I ratio of streptococcal units and leucocytes (18), was thoroughly mixed and used immediately.…”

“…When, on the other hand, the laboratory phagocytic tests are modified to simulate more closely the actual conditions which obtain Cn vivo, phagocytosis of fully encapsulated pneumococci is readily demonstrated in vitro. The principal factors which determine the validity of phagocytic tests of this kind are: (a) the absolute concentration of leucocytes in the mixture, (b) the ratio of microorganisms to leucocytes, and (c) the availability to the leucocytes of suitable surfaces against which they can trap the encapsulated organisms (18). Since virulent pneumococci and Friedlander's bacilli are phagocyted in the absence of antibody only when they can be trapped against such surfaces, the mechanism by which they are ingested has been termed "surface phagocytosis."…”

“…As in the case of the pneumococcal and Friedlander's bacillus experiments (15)(16)(17)(18), the in vitro phagocytic tests were performed in the absence of serum to avoid the possible effect of opsonins, and were carried out with washed leucocytes obtained from the same species of host in which virulence was measured. The in vivo observations were made in mice with acute streptococcal peritonitis, particular attention being paid to the earliest stages of the infection.…”