1. ^*Department of Pathophysiology-Periodontal Science, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
2. ^†Department of Global Health and Environmental Sciences-Oral Microbiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
3. ^‡Current address: Department of Dental Science for Health Promotion, Division of Cervico-Gnathostomatology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan

Correspondence: Fusanori Nishimura Department of Dental Science for Health Promotion, Division of Cervico-Gnathostomatology, Hiroshima University Graduate School of Biomedical Sciences, 1–2-3 Kasumi, Minami-ku, Hiroshima, 734-8553, Japan. E-mail: fusanori@hiroshima-u.ac.jp

^**The costs of publication of this article were defrayed, in part, by the payment of page charges. This article must, therefore, be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 20 December 2006; Accepted 7 March 2007.

Abstract

Objective: Recent studies suggested macrophages were integrated in adipose tissues, interacting with adipocytes, thereby exacerbating inflammatory responses. Persistent low-grade infection by gram-negative bacteria appears to promote atherogenesis. We hypothesized a ligand for toll-like receptor 4 (TLR4), bacterial lipopolysaccharide (LPS), would further exaggerate macrophage-adipocyte interaction.

Research Methods and Procedures: RAW264.7 macrophage cell line and differentiated 3T3-L1 preadipocytes were co-cultured using transwell system. As a control, each cell was cultured independently. After incubation of the cells with or without Escherichia coli LPS, tumor necrosis factor (TNF)- and interleukin (IL)-6 production was evaluated.

Results: Co-culture of macrophages and adipocytes with low concentration of Escherichia coli LPS (1 ng/mL) markedly up-regulated IL-6 production (nearly 100-fold higher than that of adipocyte culture alone, p < 0.01), whereas TNF- production was not significantly influenced. This increase was partially inhibited by anti-TNF- neutralizing antibody. Recombinant TNF- and LPS synergistically up-regulated IL-6 production in adipocytes. However, this increase did not reach the level of production observed in co-cultures stimulated with LPS.

Discussion: A ligand for TLR-4 stimulates macrophages to produce TNF-. TNF-, thus produced, cooperatively up-regulates IL-6 production with other soluble factors secreted either from adipocytes or macrophages in these cells. Markedly up-regulated IL-6 would greatly influence the pathophysiology of diabetes and its vascular complications.