Humoral and cellular defense against intestinal murine infection with Yersinia enterocolitica.

The role of phagocytes and the complement system as potential host defense mechanisms against bacterial infection were studied in mice with two isogenic strains of Yersinia enterocolitica serotype O8 differing in pathogenicity because of differences in plasmid content. Complement depletion in mice by intraperitoneal injection of cobra venom factor did not affect the course of colonization of the intestinal tissue by each strain, indicating that in mice complement is not essential for the elimination of these bacteria. This conclusion is supported by the fact that fresh murine serum had no bactericidal effect in vitro either on the pathogenic or on the nonpathogenic strain. However, in the intestinal tissue as well as in the peritoneal cavity, only the pathogenic, plasmid-bearing Y. enterocolitica strain survived, while the nonpathogenic, plasmidless strain was rapidly eliminated. Since elimination from the peritoneal cavity is due to phagocytosis by polymorphonuclear leukocytes and macrophages, resistance to phagocytosis in vivo seems to be the decisive factor determining the virulence of pathogenic Y. enterocolitica strains.