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Infection and Immunity, April 2001, p. 2045-2053, Vol. 69, No. 4
Department of Microbiology and Immunology,
Tohoku University School of Dentistry, Aoba-ku, Sendai
980-8575,1 Department of Immunology,
Saga Medical School, Saga 849-8501,2 and
Department of Host Defense, Research Institute for Microbial
Diseases, Osaka University, Suita, Osaka
565-0871,3 Japan
Received 29 September 2000/Returned for modification 8 November
2000/Accepted 4 January 2001
An analog of 1
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.4.2045-2053.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Synergistic Effect of Muramyldipeptide with
Lipopolysaccharide or Lipoteichoic Acid To Induce Inflammatory
Cytokines in Human Monocytic Cells in Culture
,25-dihydroxyvitamin D3,
22-oxyacalcitriol (OCT), differentiated human monocytic THP-1 and U937
cells to express membrane CD14 and rendered the cells responsive to
bacterial cell surface components. Both THP-1 and U937 cells expressed
Toll-like receptor 4 (TLR4) on the cell surface and TLR4 mRNA in the
cells, irrespective of OCT treatment. In contrast, OCT-treated U937
cells scarcely expressed TLR2 mRNA, while OCT-treated THP-1 cells
expressed this transcript. Muramyldipeptide (MDP) by itself exhibited
only a weak ability to induce secretion of inflammatory cytokines such as interleukin-8 (IL-8) in the OCT-differentiated THP-1 cells but
showed marked synergistic effects with Salmonella
lipopolysaccharide (LPS) or lipoteichoic acid (LTA) from
Staphylococcus aureus, both of which exhibited strong
activities. Combinatory stimulation with LPS plus LTA did not show a
synergistic effect on OCT-differentiated THP-1 cells. Similar results
were observed in OCT-differentiated U937 cells, although combination
experiments were carried out only with MDP plus LPS. Anti-CD14
monoclonal antibody (MAb) MY4, anti-TLR4 MAb HTA125, and the synthetic
lipid A precursor LA-14-PP almost completely inhibited the
IL-8-inducing activities of LTA as well as LPS on OCT-treated THP-1
cells, but these treatments increased MDP activity. OCT-treated THP-1
cells primed with MDP exhibited enhanced production of IL-8 upon
stimulation with LPS, while the cells primed with LPS showed no change
in production upon stimulation with MDP. MDP up-regulated mRNA
expression of an adapter molecule to TLRs, MyD88, to an extent similar
to that for LPS in OCT-treated THP-1 cells. These findings suggested
that LTA as well as LPS activated human monocytic cells in a CD14- and
TLR4-dependent manner, whereas MDP exhibited activity in a CD14-,
TLR4-, and probably TLR2-independent manner and exhibited synergistic
and priming effects on the cells for cytokine production in response to
various bacterial components.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Tohoku University School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan. Phone: 81-22-717-8305. Fax: 81-22-717-8309. E-mail:
dent-ht{at}mail.cc.tohoku.ac.jp.
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