Studies on Immunity of Experimental Typhoid

In the immunity of experimental infection of mice with Salmonella enteritidis, two kinds of mechanism were differentiated by previous studied; the role of O antibodies seemed to control the clearance phenomenon of bacteria inoculated into the peritoneal cavity, whereas the inhibition of intracellular growth of bacteriawas regarded to be of cellular nature.The local clearance phenomenon of bacteria was investigated by inoculating 32P-labelled organisms into the peritoneal cavity of mice passively immunized with anti-O serum, and by phagocytizing peritoneal cells of mice in vitro with organisms in the presence of antiserum. In the experiment with 32P-labelled organisms, the distribution of radioactivity within 6hours was not different between immunized and normal mice, but the number of living organisms in the peritoneal cavity was markedly decreased in immunized mice during that period. When peritoneal fluid was centrifuged, much higher radioactivity was detected in cell components (sediment) in immunized mice compared with normal mice.These results, together with data of the in vitro phagocytosis experiment, indicate that bacteria are rapidly phagocytosed and killed by peritoneal cells in the presence of antiserum, but not in the presence of normal serum. The antiserum alone showed no, if any, antibacterial action without living cells in the in vitro experiment.