STUDIES ON BACTERIAL LOCALIZATION

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Abstract
The results of gross and microscopic observations and survival tests after subcutaneous infection of mice with Type I pneumococci can be summarized as follows: Normal mice possessed no adequate means of protection against this organism. The bacteria disseminated freely through the tissue spaces in the presence of widespread inflammation, and were not ingested by significant numbers of host cells. Macrophages mobilized in the subcutis by intraperitoneal vaccinations with homologous killed organisms promptly ingested the living bacteria subsequently introduced. The cocci were sharply localized and destroyed in the presence of minimal amounts of exudation, edema and necrosis. Bacterial localization accompanied a similar hypoergic reaction after passive immunization. When a hyperergic response was induced by repeated local, in addition to intraperitoneal, vaccinations, prompt phagocytosis by macrophages, as after intraperitoneal vaccination alone, was again the outstanding means of disposal of the organisms. The heightened exudation, edema and local necrosis resembled a harmful rather than an important localizing reaction. Immunity was not dependent upon a hyperergic reaction. Prompt in vivo agglutination of living bacteria after passive immunization was an important early localizing phenomenon. After either active or passive immunization, phagocytosis was the only means observed by which the organisms were destroyed. Thus localization and destruction of the bacteria in immunized mice were dependent both on bacterial changes caused by specific antibody and on phagocytic activities of host cells. A viscous gum acacia medium caused a transient delay in bacterial dissemination, but the organisms ultimately became widely scattered in the tissues of the abdominal wall. The animals died earlier, with more extensive and destructive lesions than when the bacteria were introduced in a saline medium. In distinct contrast, the pneumococci were as a rule sharply localized and destroyed when injected in an acacia medium containing a small amount of immune serum. After local active immunization, sufficient to protect about half the animals subsequently infected by pneumococci in a saline medium, extensive and destructive lesions and death of the mice followed introduction of the organisms in acacia. It was suggested that the more viscous medium may have hindered diffusion of immune bodies from the tissues into the inoculum.

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