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Infect. Immun., Feb 1996, 452-459, Vol 64, No. 2
P Laochumroonvorapong, S Paul, KB Elkon and G Kaplan
Mycobacterium avium-M. intracellulare, an intracellular parasite of
mononuclear phagocytes, rarely causes disease in immunocompetent
individuals. In contrast, in human immunodeficiency virus type 1- infected
patients, M. avium-M. intracellulare can infect almost every tissue and
organ. This suggests that immunocompetent individuals have a protective
mechanism to control or prevent the infection. How mycobacterial may be
killed by the host immune response is unclear. We have recently reported
that induction of apoptosis of Mycobacterium bovis BCG-infected macrophages
with ATP4- was associated with killing of the intracellular mycobacteria.
In the present study, a long-term culture of M. avium-M.
intracellulare-infected monocytes was used to further evaluate the
interaction between M. avium-M. intracellulare and primary human monocytes.
In our system, M. avium-M. intracellulare parasitized the human monocytes
and appeared to replicate slowly over 14 days within the host cells. To
examine the role of apoptotic mechanisms in survival or death of
intracellular mycobacteria, M. avium- M. intracellulare-infected human
monocytes were treated with a monoclonal antibody to Fas receptor
(APO-1/CD95) or with various concentrations of H2O2. Although both of these
exogenous agents induced monocyte apoptosis, optimal killing (65% reduction
in CFU) of intracellular M. avium-M. intracellulare was observed only when
M. avium-M. intracellulare-infected cells were treated with 10 mM H2O2.
Fas-induced apoptosis did not affect M. avium-M. intracellulare viability.
Our results suggest that not all stimuli of monocyte apoptosis induce
killing of intracellular M. avium-M. intracellulare. Since release of H2O2
following phagocytosis of mycobacteria has been documented, H2O2-induced
apoptotic death of M. avium-M. intracellulare- infected monocytes and its
association with killing of the intracellular bacilli may be a
physiological mechanism of host defense against M. avium-M. intracellulare.
Copyright © 1996, American Society for Microbiology
H2O2 induces monocyte apoptosis and reduces viability of Mycobacterium avium-M. intracellulare within cultured human monocytes
Laboratory of Cellular Physiology and Immunology, Rockefeller University, New York, New York, USA.
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