A single tissue culture system for the propagation of the agents of the human ehrlichioses

Two newly emergent human diseases found in the United States, human monocytotropic ehrlichiosis (HME) and human granulocytotropic ehrlichiosis (HGE), are caused by pathogens of the genus Ehrlichia. The causative agent of HGE can be propagated in HL-60 human promyelocytic leukemia cells. Herein, we report the development of a method to propagate E. chaffeensis, the causative agent of HME, in HL-60 cells, thus providing a common system for the study of both species. The continuous propagation of E. chaffeensis requires the induction of HL-60 differentiation along the monocytic pathway toward phenotypically mature macrophages by the addition of 25-OH vitamin D-3 to the growth medium.