Interactions of Gut Microbiota, Endotoxemia, Immune Function, and Diet in Exertional Heatstroke

Figure 4

Many compounds other than lipopolysaccharide (LPS) can bind to a proinflammatory receptor on immune cells, TLR-4 (toll-like receptor-4). When TLR-4 and its accessory proteins, including lymphocyte antigen 96 (MD-2), are triggered by some of these compounds, two main pathways through initial signaling proteins MyD88 (myeloid differentiation primary response gene 88) and TRIF (TIR domain containing adaptor-inducing interferon-beta) stimulate a cascade of signaling to multiple proteins. The end result involves proteins that enter the nucleus, bind to DNA, and change gene expression to stimulate the production of proinflammatory proteins. Structural variations in LPS molecules can affect how robustly this response occurs, by affecting the strength of binding at TLR-4 to stimulate the initial signal. Additionally, other molecules or proteins may independently affect the strength of the proinflammatory response to LPS. MAPK (mitogen associated protein kinase); NFκB (nuclear factor kappa light chain enhancer of activated B-cells); IRF3 (interferon regulatory factor 3); AP-1 (activator protein 1).