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Infection and Immunity, October 2000, p. 5673-5678, Vol. 68, No. 10
Unité des Rickettsies, CNRS UPRESA
6020, Faculté de Médecine, Université de la
Méditerranée, 13385 Marseille Cedex 05, France,1 and Department of
Rickettsiology and Chlamydiology, Institute of Virology, Slovak
Academy of Sciences, 842 45 Bratislava, Slovak
Republic2
Received 10 April 2000/Accepted 26 June 2000
Coxiella burnetii, the agent of Q fever, enters human
monocytes through
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
v
3 Integrin and
Bacterial Lipopolysaccharide Are Involved in Coxiella
burnetii-Stimulated Production of Tumor Necrosis Factor by
Human Monocytes
v
3 integrin and
survives inside host cells. In addition, C. burnetii
stimulates the synthesis of inflammatory cytokines including tumor
necrosis factor (TNF) by monocytes. We studied the role of the
interaction of C. burnetii with THP-1 monocytes in TNF
production. TNF transcripts and TNF release reached maximum values
within 4 h. Almost all monocytes bound C. burnetii
after 4 h, while the percentage of phagocytosing monocytes did not
exceed 20%. Cytochalasin D, which prevented the uptake of C. burnetii without interfering with its binding, did not affect the
expression of TNF mRNA. Thus, bacterial adherence, but not
phagocytosis, is necessary for TNF production by monocytes. The
monocyte
v
3 integrin was involved in TNF
synthesis since peptides containing RGD sequences and blocking
antibodies against
v
3 integrin inhibited TNF transcripts induced by C. burnetii. Nevertheless, the
cross-linking of
v
3 integrin by specific
antibodies was not sufficient to induce TNF synthesis. The signal
delivered by C. burnetii was triggered by bacterial
lipopolysaccharide (LPS). Polymyxin B inhibited the TNF production
stimulated by C. burnetii, and soluble LPS isolated from
C. burnetii largely mimicked viable bacteria. On the other
hand, avirulent variants of C. burnetii induced TNF production through an increased binding to monocytes rather than through the potency of their LPS. We suggest that the adherence of
C. burnetii to monocytes via
v
3 integrin enables surface LPS to
stimulate TNF production in THP-1 monocytes.
*
Corresponding author. Mailing address: Unité des
Rickettsies, CNRS UPRESA 6020, Faculté de Médecine, 27 Bd
Jean Moulin, 13385 Marseille Cedex 05, France. Phone: (33) 4 91 32 43 75. Fax: (33) 4 91 38 77 72. E-mail:
Jean-Louis.Mege{at}medecine.univ-mrs.fr.
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