Interaction of Rickettsiae and Phagocytic Host Cells

Abstract

Summary In contrast to the focal perivascular collections of mononuclear cells which constitute the classical basic lesion seen in persons dying of typhus fevers, the initial cellular response in man to the presence of typhus rickettsiae, as revealed by the skin window technique, consisted of a typical acute inflammatory reaction. Polymorphonuclear leukocytes appeared within 1.5 hr after introduction of the organisms and increased in numbers during the first 24 hr. Although mononuclear cells began to appear in the lesions between 6 and 12 hr, the polymorphonuclear leukocyte remained the dominant cell throughout the 24-hr observation period. The main difference between the responses of susceptible and immune subjects lay in the more intense polymorphonuclear reaction in the immune subjects. In vivo phagocytosis of living and dead rickettsiae was demonstrable with both polymorphonuclear and larger mononuclear cells in immune as well as nonimmune subjects. The experimental conditions employed reproduced closely the conditions which obtain at the time of natural infection. The implications of these findings with regard to host defense reactions against typhus rickettsiae are discussed.