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Infection and Immunity, March 2001, p. 1287-1297, Vol. 69, No. 3
Department of Immunology, Polish-American
Institute of Paediatrics,1 and
Department of Microbiology and Immunology, Institute of
Molecular Biology,2 Jagiellonian University,
Cracow, Poland, and Department of Immunology and Cell Biology,
Forschungszentrum Borstel, Borstel, Germany3
Received 28 June 2000/Returned for modification 6 September
2000/Accepted 27 November 2000
Human peripheral blood monocytes become apoptotic following
phagocytosis of Staphylococcus aureus. In this study, we
investigated the mechanisms involved in this phenomenon. Cells exposed
to bacteria were examined for the surface expression of Fas and Fas
ligand (FasL). The level of soluble form of FasL was also measured in the culture supernatants. As Fas-mediated apoptosis involves the activation of caspases, the activities of caspase-8 and caspase-3 were
determined. Finally, the involvement of oxidative stress in apoptosis
of infected monocytes was investigated. The data indicated that as a
consequence of phagocytosis of S. aureus, FasL is released
from the monocyte surface and induces apoptosis of phagocytic monocytes
and to some extent the bystander cells. The importance of this
mechanism was confirmed by demonstrating that blockage of CD95 prevents
S. aureus-induced apoptosis of monocytes. Cell death
occurring after phagocytosis of S. aureus involves the
activation of caspase-3-like proteases, as the specific caspase-3
inhibitor suppressed apoptosis of infected cells. The generation of
reactive oxygen intermediates by phagocytic monocytes by itself is not
sufficient as a death signal but rather acts in up-regulating FasL
shedding and possibly in modulating caspase activity.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.3.1287-1297.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Fas (CD95)-Fas Ligand Interactions Are Responsible
for Monocyte Apoptosis Occurring as a Result of Phagocytosis and
Killing of Staphylococcus aureus
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Institute of Molecular Biology,
Jagiellonian University, Al. Mickiewicza 3, 31-120 Cracow, Poland.
Phone: (4812) 6341662, ext. 258. Fax: (4812) 6336907. E-mail:
PRYJMA{at}mol.uj.edu.pl.
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