Differential Induction of the Toll-Like Receptor 4-MyD88-Dependent and -Independent Signaling Pathways by Endotoxins

• Published in: Infection and Immunity Vol. 73; no. 5; pp. 2940 - 2950
• Main Authors: Zughaier, Susu M, Zimmer, Shanta M, Datta, Anup, Carlson, Russell W, Stephens, David S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.05.2005
• Subjects: Adaptor Proteins, Signal Transducing; Animals; Antigens, Differentiation - metabolism; Biological and medical sciences; Cell Line; Cellular Microbiology: Pathogen-Host Cell Molecular Interactions; Cytokines - metabolism; Endotoxins - chemistry; Endotoxins - physiology; Escherichia coli; Fundamental and applied biological sciences. Psychology; Gram-Negative Bacteria - immunology; Gram-Negative Bacteria - metabolism; Gram-Negative Bacteria - pathogenicity; Humans; Lipid A - chemistry; Lipid A - pharmacology; Lipopolysaccharides - chemistry; Macrophage Activation - drug effects; Macrophage Activation - immunology; Macrophages - immunology; Macrophages - metabolism; Membrane Glycoproteins - metabolism; Mice; Mice, Inbred C3H; Microbiology; Myeloid Differentiation Factor 88; Neisseria meningitidis; Nitric Oxide - metabolism; Receptors, Cell Surface - metabolism; Receptors, Immunologic - metabolism; Salmonella enterica; Signal Transduction; Toll-Like Receptor 4; Toll-Like Receptors; Vibrio cholerae; Toxin; Toll like receptor; Microbiology; Endotoxin; Immunity
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/iai.73.5.2940-2950.2005

The biological response to endotoxin mediated through the Toll-like receptor 4 (TLR4)-MD-2 receptor complex is directly related to lipid A structure or configuration. Endotoxin structure may also influence activation of the MyD88-dependent and -independent signaling pathways of TLR4. To address this possibility, human macrophage-like cell lines (THP-1, U937, and MM6) or murine macrophage RAW 264.7 cells were stimulated with picomolar concentrations of highly purified endotoxins. Harvested supernatants from previously stimulated cells were also used to stimulate RAW 264.7 or 23ScCr (TLR4-deficient) macrophages (i.e., indirect induction). Neisseria meningitidis lipooligosaccharide (LOS) was a potent direct inducer of the MyD88-dependent pathway molecules tumor necrosis factor alpha (TNF-[alpha]), interleukin-1{szligbeta} (IL-1{szligbeta}), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein 3[alpha] (MIP-3[alpha]), and the MyD88-independent molecules beta interferon (IFN-{szligbeta}), nitric oxide, and IFN-[gamma]-inducible protein 10 (IP-10). Escherichia coli 55:B5 and Vibrio cholerae lipopolysaccharides (LPSs) at the same pmole/ml lipid A concentrations induced comparable levels of TNF-[alpha], IL-1{szligbeta}, and MIP-3[alpha], but significantly less IFN-{szligbeta}, nitric oxide, and IP-10. In contrast, LPS from Salmonella enterica serovars Minnesota and Typhimurium induced amounts of IFN-{szligbeta}, nitric oxide, and IP-10 similar to meningococcal LOS but much less TNF-[alpha] and MIP-3[alpha] in time course and dose-response experiments. No MyD88-dependent or -independent response to endotoxin was seen in TLR4-deficient cell lines (C3H/HeJ and 23ScCr) and response was restored in TLR4-MD-2-transfected human embryonic kidney 293 cells. Blocking the MyD88-dependent pathway by DNMyD88 resulted in significant reduction of TNF-[alpha] release but did not influence nitric oxide release. IFN-{szligbeta} polyclonal antibody and IFN-[alpha]/{szligbeta} receptor 1 antibody significantly reduced nitric oxide release. N. meningitidis endotoxin was a potent agonist of both the MyD88-dependent and -independent signaling pathways of the TLR4 receptor complex of human macrophages. E. coli 55:B5 and Vibrio cholerae LPS, at the same picomolar lipid A concentrations, selectively induced the MyD88-dependent pathway, while Salmonella LPS activated the MyD88-independent pathway.