Infectious process in the lungs after intranasal challenge of white mice with Rickettsia prowazekii. A histologic immunoluminescent and electron microscopic study.

The lungs of white mice given intranasal injections of various amounts of Rickettsia prowazekii were studied. Agent parasitism, mainly in the alveolar epithelium and nonciliated cells of bronchiolar epithelium, underlies the infectious process developing in the lungs. Rickettsiae may lodge in these cells without inducing both local and general alterations or a leukocyte response. After being released from the cells they inhabit, rickettsiae evoke acute exudative inflammation. The inflammation is accompanied by marked circulatory disorders, necrosis of exudate cells and vascular thrombosis, which are induced by toxic products of the agent. Polymorphonuclear leukocytes and macrophages represent the main defense mechanism of a host. They ingest and destroy rickettsial organisms. If infection runs a favorable course, phagocytes destroy the rickettsiae, and the organisms are entirely cleared from the lungs.