Electron Microscopic Studies on Mechanismof Phagocytosis

The mechanism of phagocytosis and the intracellular fate of bacteria were investigated electron microscopically. The cells used were Tetrahymena vorax, rabbit neutrophils, mouse peritoneal macrophage and various tissue culture cells including HeLa, L, FL, vero and primary dog kidoney cells. Staphylococcus aureus 209P was used in the adsorption studies. The results obtained were as follows : 1) The attachment to the microvilli or to the cell surface of the test particles was an essential first step of phagocytosis. To the microvilli of HeLa cells, staphylococcus aureus attached and hence was ingested well, whereas Staphylococcus epidermidis did not attach and hence could not be ingested. Sepia melanin particles did not attach efficiently and hence were taken up poorly. Macrophages, on the other hand, absorbed and took up well the two strains of staphylococci and melanin particles. 2) The attachment to the microvilli of the tissue culture cells of Staphylococcus aureus was followed by its attachment to the cell surface and then the invagination under the coccus and simultaneous membraneous elevation of the cell surface around the cocci resulting the formation of acrater(caeola). The mechanism of the invagination and the formation of phagosomes of tissue culture cells were essentially similar to that observed with macrophages. 3) Staphylococcus aureus ingested by Tetrahymena was digested quickly by lysosomal enzymes leaving membraneous configurations which eventually extruded in the form of defecation balls. 4) Digestion by lysosomal enzymes of staphylococci inside the phagosome of tissue culture cells was also observed, although the digree was much slighter than those observed in Tetrahymena. 5) After the digestion of radio active uridine labelled staphylococci by Tetrahymena, the radio activities were observed to be distributed among the cytoplasma and the nucleus indicating that digested substances had passed outside the phagosomes and had been utilized by the cells. Radio active uridine outside the phagosomes was also recognized in macrophages and L cells.