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Abstract

Members of the Toll-like receptor (TLR) family are key regulators of both innate and adaptive immune responses. The function of TLRs in various human diseases has been investigated by comparison of the incidence of disease among people having different polymorphisms in genes that participate in TLR signaling. These studies have shown that TLR function affects several diseases, including sepsis, immunodeficiencies, atherosclerosis and asthma. As this body of data grows, it will provide new insights into disease pathogenesis as well as valuable information on the merits of various therapeutic options.

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Regulatory T Cells Selectively Express Toll-like Receptors and Are Activated by Lipopolysaccharide

Iris Caramalho, Thiago Lopes-Carvalho, Dominique Ostler … (2003)

Regulatory CD4 T cells (Treg) control inflammatory reactions to commensal bacteria and opportunist pathogens. Activation of Treg functions during these processes might be mediated by host-derived proinflammatory molecules or directly by bacterial products. We tested the hypothesis that engagement of germline-encoded receptors expressed by Treg participate in the triggering of their function. We report that the subset of CD4 cells known to exert regulatory functions in vivo (CD45RBlow CD25+) selectively express Toll-like receptors (TLR)-4, -5, -7, and -8. Exposure of CD4+ CD25+ cells to the TLR-4 ligand lipopolysaccharide (LPS) induces up-regulation of several activation markers and enhances their survival/proliferation. This proliferative response does not require antigen-presenting cells and is augmented by T cell receptor triggering and interleukin 2 stimulation. Most importantly, LPS treatment increases CD4+ CD25+ cell suppressor efficiency by 10-fold and reveals suppressive activity in the CD4+ CD45RBlow CD25− subset that when tested ex-vivo, scores negative. Moreover, LPS-activated Treg efficiently control naive CD4 T cell–dependent wasting disease. These findings provide the first evidence that Treg respond directly to proinflammatory bacterial products, a mechanism that likely contributes to the control of inflammatory responses.

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Toll-like receptor 4 polymorphisms and atherogenesis.

Johann Willeit, Eva Lorenz, Friedrich Oberhollenzer … (2002)

The ability to mount a prominent inflammatory response to bacterial pathogens confers an advantage in innate immune defense but may signal an increased risk of atherosclerosis. We determined whether recently discovered genetic variants of toll-like receptor 4 (TLR4) that confer differences in the inflammatory response elicited by bacterial lipopolysaccharide are related to the development of atherosclerosis. As part of the five-year follow-up in the Bruneck (Italy) Study, we screened 810 persons in the study cohort for the TLR4 polymorphisms Asp299Gly and Thr399Ile. The extent and progression of carotid atherosclerosis were assessed by high-resolution duplex ultrasonography. As compared with subjects with wild-type TLR4, the 55 subjects with the Asp299Gly TLR4 allele had lower levels of certain proinflammatory cytokines, acute-phase reactants, and soluble adhesion molecules, such as interleukin-6 and fibrinogen. Although these subjects were found to be more susceptible to severe bacterial infections, they had a lower risk of carotid atherosclerosis (odds ratio, 0.54; 95 percent confidence interval, 0.32 to 0.98; P=0.05) and a smaller intima-media thickness in the common carotid artery (regression coefficient, -0.07; 95 percent confidence interval, -0.12 to -0.02; P=0.01). The Asp299Gly TLR4 polymorphism, which attenuates receptor signaling and diminishes the inflammatory response to gram-negative pathogens, is associated with a decreased risk of atherosclerosis. This finding is consistent with the hypothesis that innate immunity may play a part in atherogenesis. Copyright 2002 Massachusetts Medical Society.

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Toll-like receptor-4 is expressed by macrophages in murine and human lipid-rich atherosclerotic plaques and upregulated by oxidized LDL.

O Equils, T Rajavashisth, D Luthringer … (2001)

Inflammation is implicated in atherogenesis and plaque disruption. Toll-like receptor 2 (TLR-2) and TLR-4, a human homologue of drosophila Toll, play an important role in the innate and inflammatory signaling responses to microbial agents. To investigate a potential role of these receptors in atherosclerosis, we assessed the expression of TLR-2 and TLR-4 in murine and human atherosclerotic plaques. Aortic root lesions of high-fat diet-fed apoE-deficient mice (n=5) and human coronary atherosclerotic plaques (n=9) obtained at autopsy were examined for TLR-4 and TLR-2 expression by immunohistochemistry. Aortic atherosclerotic lesions in all apoE-deficient mice expressed TLR-4, whereas aortic tissue obtained from control C57BL/6J mice showed no TLR-4 expression. All 5 lipid-rich human plaques expressed TRL-4, whereas the 4 fibrous plaques and 4 normal human arteries showed no or minimal expression. Serial sections and double immunostaining showed TLR-4 colocalizing with macrophages both in murine atherosclerotic lesions and at the shoulder region of human coronary artery plaques. In contrast to TLR-4, none of the plaques expressed TLR-2. Furthermore, basal TLR-4 mRNA expression by human monocyte-derived macrophages was upregulated by ox-LDL in vitro. Our study demonstrates that TLR-4 is preferentially expressed by macrophages in murine and human lipid-rich atherosclerotic lesions, where it may play a role to enhance and sustain the innate immune and inflammatory responses. Moreover, upregulation of TLR-4 in macrophages by oxidized LDL suggests that TLR-4 may provide a potential pathophysiological link between lipids and infection/inflammation and atherosclerosis.

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PubMed ID:: 15454920

DOI:: 10.1038/ni1116

ScienceOpen disciplines: Chemistry

Keywords: Animals,Arteriosclerosis,etiology,Asthma,Autoimmune Diseases,Bacterial Infections,Humans,I-kappa B Kinase,Immune Tolerance,Membrane Glycoproteins,physiology,Protein-Serine-Threonine Kinases,Receptors, Cell Surface,Sepsis,Toll-Like Receptors

Toll-like receptors in the pathogenesis of human disease.

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Most cited references 38

Regulatory T Cells Selectively Express Toll-like Receptors and Are Activated by Lipopolysaccharide

Toll-like receptor 4 polymorphisms and atherogenesis.

Toll-like receptor-4 is expressed by macrophages in murine and human lipid-rich atherosclerotic plaques and upregulated by oxidized LDL.

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