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(Journal of Leukocyte Biology. 2001;69:397-404.)
© 2001 by Society for Leukocyte Biology

Phagocytosis and killing of Mycobacterium avium complex by human neutrophils

Pia Hartmann^*, Ralph Becker^*, Caspar Franzen^*, Elisabeth Schell-Frederick^*, Jens Römer^*, Michaela Jacobs^*, Gerd Fätkenheuer^* and Georg Plum

Departments of
^* Internal Medicine I and
Medical Microbiology and Hygiene, University of Cologne, Germany

Correspondence: Pia Hartmann, M.D., Department of Internal Medicine I, Division of Infectious Diseases, Joseph-Stelzmann-Strasse 9, 50924 Cologne, Germany.

Organisms belonging to the Mycobacterium avium complex (MAC) cause life-threatening bacteremia in immunocompromised patients. Monocytes and macrophages are thought to be responsible for ingestion and killing of MAC. However, it has been suggested that neutrophils may play a role in the early immune response to MAC infection. Here, neutrophils in autologous plasma were incubated (at 0 and 37°C) with M. avium labeled with Auramine O, a potent fluorochrome. Neutrophil phagocytosis was measured by flow cytometry. Neutrophils incubated at 37°C showed an increase in fluorescence over time with a maximum at 15 min, whereas neutrophils on ice showed no time-dependent increase in FL1. At 15 min Fl 1 at 37°C was twice as high as FL1 at 0°C. Examination under the fluorescent microscope showed multiple intracellular fluorescent mycobacteria. Results in nine independent experiments showed time-dependent decrease of colony-forming units in neutrophil-associated live M. avium. Significant killing was observed within 30 min and was complete by 120 min. Observation by electron microscopy clearly confirmed the presence of intraphagosomal MAC, both intact and with evidence of degradation. These data demonstrate that MAC is rapidly phagocytized and killed by human neutrophils. The newly established flow cytometry method should be useful in further studies of neutrophil function and of the role of G-CSF and other cytokines in MAC disease.

Key Words: granulocytes • host defense • atypical mycobacteria

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