Experimental model for dermal granulomatous hypersensitivity in Q fever.

Q fever has been associated with granulomatous changes in clinical biopsy material obtained from liver and bone marrow. Local reactions to skin testing have been described in previously sensitized humans, but histological studies of such reactions have not been reported. We note that delayed hypersensitivity reactions to whole-cell phase I Q fever vaccine in immunized guinea pigs have a time course of development of induration characteristic of granulomatous hypersensitivity. Histological examination of such skin reactions on day 9 after testing revealed epithelioid cell infiltration and the presence of large numbers of multinucleated giant cells. Prominent in the sections were fragments of disintegrating polymorphonuclear leukocytes having the appearance of leukocytoclasis. Electron microscopic studies confirmed the presence of epithelioid changes in cells of the mononuclear phagocyte series, as well as extensive collagen deposition. This animal system affords a readily reproducible model of dermal granulomatous hypersensitivity and an opportunity to analyze the immunological basis of this reaction.