Gross and Microscopic Skin Reactions to Killed Typhus Rickettsiae in Human Beings

Summary Studies of the skin reactions produced by formalin-killed suspensions of Rickettsia mooseri and Rickettsia prowazekii in normal human subjects and in subjects with various kinds of previous experience with typhus organisms have yielded the following observations: Relatively concentrated rickettsial suspensions produce local “toxic” reactions in the skin of normal subjects which are compatible with an endotoxic component in the organisms.Subjects with previous typhus experience exhibit a markedly enhanced local and systemic reactivity to the typhus antigens. Thir reaction is compatible with a delayed type hypersensitivity to typhus antigens.Histologic studies of skin biopsies taken from different subjects at various times after injection of test material revealed an early inflammatory response in normal subjects compatible with that induced by endotoxins and a delayed inflammatory response in hypersensitive subjects compatible with a reaction of delayed type hypersensitivity.The skin reaction did not distinguish between murine and epidemic typhus, suggesting that the major antigen(s) involved is common to both species of organism.The delayed type hypersensitivity to typhus antigens developed with regularity following vaccination with the attenuated living E strain of R. prowazekii, a positive reaction often appearing as early as 7 to 10 days following vaccination.