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In vivo and in vitro studies on Anaplasma phagocytophilum infection of the myeloid cells of a patient with chronic myelogenous leukaemia and human granulocytic ehrlichiosis

¹ Department of Pathology, New York Medical College, Westchester Medical Center, Valhalla, New York 10595, USA
² Department of Medicine, New York Medical College
³ Division of Infectious Diseases, New York Medical College
⁴ Division of Biochemistry and Molecular Biology, New York Medical College
⁵ Department of Pediatrics, Cornell Medical Center, 525E 68th Street, New York, NY 10021, USA

Correspondence to:
Dr M E Aguero-Rosenfeld
Clinical Laboratories Room 1J-04, Westchester Medical Center, Valhalla, NY 10595, USA; m_aguero-rosenfeld{at}nymc.edu Aims: The occurrence of human granulocytic ehrlichiosis (HGE) in a patient with chronic myelogenous leukaemia (CML) provided an opportunity to study whether Anaplasma phagocytophilum, the aetiological agent of HGE, infects mature or immature cells, both in vivo and in vitro.

Methods: Diagnosis of HGE was confirmed by culture, polymerase chain reaction (PCR), detection of intragranulocytic inclusions, and serology. The infection rates of different myelogenous stages of granulocytic differentiation were determined by microscopy. Anaplasma phagocytophilum infection of the bone marrow was analysed by PCR, culture, and microscopy. In addition, the in vitro growth of A phagocytophilum in the patient’s granulocytes and in HL-60 cells (a promyelocytic leukaemia cell line) was compared.

Results: Pretreatment blood smears showed that mature granulocytic cells had a higher infection rate with A phagocytophilum than did immature cells. In the original inoculation of the patient’s cells into HL-60 cells to isolate A phagocytophilum, the bacterium grew faster in the patient’s leukaemic cells than in HL-60 cells. Anaplasma phagocytophilum inclusions were rarely seen in bone marrow granulocytes and PCR was negative. In vitro, two A phagocytophilum isolates grew faster in the patient’s granulocytes than in HL-60 cells.

Conclusions: The superior growth in CML cells compared with HL-60 cells suggests that A phagocytophilum preferentially infects mature granulocytes. The higher infection rate of the patient’s mature versus immature granulocytes before treatment and the minimal level of infection of the patient’s bone marrow support this. It is possible that the primary site of infection in HGE is the peripheral mature granulocytic population.

Abbreviations: CML, chronic myelogenous leukaemia; HGE, human granulocytic ehrlichiosis; PCR, polymerase chain reaction; PSGL-1, P selectin glycoprotein ligand-1; WBC, white blood cell count