Antibody-dependent cellular cytotoxicity of Coxiella burnetii-infected J774 macrophage target cells

Abstract

By using a mouse macrophage tumor cell line, J774, persistently infected with C. burnetii phase I organisms, in a standard 51Cr-release cytotoxicity assay, the possibility that antibody-dependent cellular cytotoxicity may be an immune mechanism in Q fever was explored. After 16 h of incubation in the presence of immune sera from Q fever hepatitis or endocarditis patients, nonimmune human peripheral blood effector cells specifically lysed infected J774 target cells; no 51Cr release was seen in the presence of nonimmune sera or uninfected target cells. An effector/target ratio of at least 5:1 was required; monocytes were more efficient effector cells than lymphocytes. Cytotoxicity was blocked by preincubation of effector cells with purified aggregated human IgG, indicating the role of Fc receptor-bearing effector cells. Two nonphagocytic lymphoid tumor cell targets, passively coated with C. burnetii, did not induce substantial immune-specific cytolysis, suggesting that cytotoxicity may participate in primary defense, alternatively, it may facilitate the dissemination of C. burnetii or surreptitiously participate in granuloma formation.