PRIMARY BONE-MARROW PROGENITORS OF BOTH GRANULOCYTIC AND MONOCYTIC LINEAGES ARE SUSCEPTIBLE TO INFECTION WITH THE AGENT OF HUMAN GRANULOCYTIC EHRLICHIOSIS

Human granulocytic ehrlichiosis (HGE) is an emerging tickborne infecti on resulting in an acute febrile illness associated with cytopenias an d characteristic intracellular organisms within peripheral blood granu locytes. The etiologic agent of HGE has recently been isolated and cul tivated in the HL-60 promyelocytic leukemia cell line, but the spectru m of host cells that it naturally infects remains unknown, To determin e if normal hematopoietic progenitors could be targets of infection, C D34(+) primary human bone marrow cells, stimulated to differentiate al ong myelomonocytic lineages, were incubated with the HGE agent, Immatu re marrow progenitors and, remarkably, not only granulocytic but also CD14(+) monocytic cells from these cultures supported replication of t he HGE agent, suggesting that all are potential targets of infection i n vivo, Infection of bone marrow progenitors may contribute to the hem atologic manifestations of HGE, Furthermore, the ability of the agent to interact with monocytes has significant implications regarding dise ase pathogenesis and host response.