Infection of human monocyte-derived macrophages with Coxiella burnetii.

Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that has a tropism for cells of the mononuclear phagocyte system. Following internalization, C. burnetii remains in a phagosome that ultimately matures into a vacuole with lysosomal characteristics that supports pathogen replication. Most in vitro investigations of Coxiella - macrophage interactions have employed continuous cell lines. Although these studies have been informative, genetic alterations of immortalized cells may result in attenuated biological responses to infection relative to primary cells. Consequently, primary macrophages are preferred as in vitro model systems. Here, we describe procedures for propagation and isolation of C. burnetii from cell culture and the use of these preparations to infect primary macrophages derived from human peripheral blood monocytes. Both virulent phase I and avirulent phase II C. burnetii productively infect human monocyte-derived macrophages (MDMs) and replicate with approximately the same kinetics, thereby providing a more physiologically relevant in vitro model system to study the infectious process of this pathogen.