Recent advances in endotoxin tolerance

Endotoxin tolerance is defined as a reduced capacity of a cell to respond endotoxin (lipopolysaccharide, LPS) challenge after an initial encounter with endotoxin in advance. The body becomes tolerant to subsequent challenge with a lethal dose of endotoxin and cytokines release and cell/tissue damage induced by inflammatory reaction are significantly reduced in the state of endotoxin tolerance. The main characteristics of endotoxin tolerance are downregulation of inflammatory mediators such as tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), and C-X-C motif chemokine 10 (CXCL10) and upregulation of anti-inflammatory cytokines such as IL-10 and transforming growth factor β (TGF-β). Therefore, endotoxin tolerance is often regarded as the regulatory mechanism of the host against excessive inflammation. Endotoxin tolerance is a complex pathophysiological process and involved in multiple cellular signal pathways, receptor alterations, and biological molecules. However, the exact mechanism remains elusive up to date. To better understand the underlying cellular and molecular mechanisms of endotoxin tolerance, it is crucial to investigate the comprehensive cellular signal pathways, signaling proteins, cell surface molecules, proinflammatory and anti-inflammatory cytokines, and other mediators. Endotoxin tolerance plays an important role in reducing the mortality of sepsis, endotoxin shock, and other endotoxin-related diseases. Recent reports indicated that endotoxin tolerance is also related to other diseases such as cystic fibrosis, acute coronary syndrome, liver ischemia-reperfusion injury, and cancer. The aim of this review is to discuss the recent advances in endotoxin tolerance mainly based on the cellular and molecular mechanisms by outline the current state of the knowledge of the involvement of the toll-like receptor 4 (TLR4) signaling pathways, negative regulate factor, microRNAs, apoptosis, chromatin modification, and gene reprogramming of immune cells in endotoxin tolerance. We hope to provide a new idea and scientific basis for the rational treatment of endotoxin-related diseases such as endotoxemia, sepsis, and endotoxin shock clinically.