Relationship Between GUT Associated Dendritic Cells And Intestinal Immune Barrier Dysfunction After Trauma/Hemorrhagic Shock

BackgroundIt’s well known that Trauma/hemorrhagic shock (TH/S) is associated with immunosuppression, which can render patients susceptible to nosocomial infection and multiorgan dysfunction. We have previously demonstrated in a rat model of TH/S the typical differentiation towards Th2phenotype in the T-cell population with an associated increase in the apoptosis of CD4+T-cells. However, the mechanisms leading to TH/S immunosuppression are poorly understood.As one of the most vulnerable organs under ischemia reperfusion injury, an organ access to the largest amount of bacteria and one of the largest immune organ, the gut has been hypothesized to be the "motor" of nosocomial infection and multiple organ dysfunction syndrome (MODS). Under the attacking of ischemia reperfusion and pathogen, the destroyed mucosal immune system (including dendritic cells and epithelium) will induce local and systemic immunosuppression consequent with bacterial translocation.MLN-DCs and LPDCs as the main part of gut associated DCs are thought to be critical in "decision" of whether to tolerant or protective immune response in the intestinal immune barrier. A subset of CD11chiCD11bhi lamina propria dendritic cells (LPDCs) discovered by Satoshi Uematsu has been identified that expressed Toll-like receptor5(TLR5) in the small intestine. When stimulated by the TLR5ligand flagellin, TLR5+LPDCs can induce the differentiation of naive B cells into immunoglobulin A-producing plasma cells and of antigen-specific interleukin17-producing T helper cells and type1T helper cells. More interesting, unlike spleen DCs, the LPDCs specifically produced retinoic acid (RA), which is regulated by Tlr5-Myd88signaling system and in a dose-dependent way regulated the differentiation interleukin17-producing T helper cells in the lamina propria.The adult human intestine is home to more than100trillion bacteria, which dwarves the number of somatic and germ cells in the entire human organism. There are estimated to be between500-1000species of bacteria present in our intestines. Aerobic, facultative, and anaerobic bacteria are all part of the enteric microflora. It was found that broad-spectrum antibiotics were able to promote the development of pathogenic bacteria, which will finally induce infectious diarrhea and extraenteric infections.We make a hypothesis that weakness of intestinal immune barrier and disorder of immune state of the body induced by TH/S companied with the large number of intestinal pathogenic bacteria growth result in the increase the bacterial translocation and severe infection, and the mechanism of the hypothesis needs conclusive evidence. Aim:With the gut associated dendritic cells and intestinal epithelial cells as the key cells of intestinal immune barrier, the disfunction of dendritic cells and intestinal mucosal damage induced by intestinal bacteria as the two research thinking, this study will try find out the important mechanism of the injury of intestinal immune barrier and bacterial translocation after traumatic shock. Methods:1) Evaluate the effects of TH/S on the function of MLN-DCs in a Sprague-Dawley rat model with mid-diaphyseal transverse fracture and an MAP of3±5mmHg for90min. MLN-DCs were evaluated for surface expression of CD80, CD86, and MHC II, as well as for apoptosis. The in-vitro and in-vivo effects of MLN-DCs-induced induction of CD4T cell differentiation, and the underlying mechanisms were investigated.2) Under the help of TH/S mice model and TLR5-/-KO mice, this study used the LPDCs as the key cells with the characteristic of Toll-like5receptor and retinoic acid (RA) production, which is regulated by T1r5-Myd88signaling system and in a dose-dependent way regulated the differentiation of thl and th17cells. Eexamined the effects of TH/S on the function of LPDCs on induction of CD4T cell differentiation especially TH1and TH17, and the underlying mechanisms such as the RALDH synthetic ability. Additionally the intra-intestinal bacterial translocation was monitored using bioluminescent citrobacter and IVIS Spectrum optical imaging system.3) Several VRE samples which induced severe enteritis and extraenteric disseminations were used to infect the human intestinal Caco-2cell line, followed by inflammatory cytokine assays and morphological characterization by electron microscopy.Results:1) T/HS-induced increase in early apoptosis of MLN-DCs which was likely mediated by cleaved-caspase-3and-9, AKT and ERK. CD80and MHC-II expression levels were downregulated in the T/HS group compared to the SHAM, Importantly, MLN-DCs from T/HS rats promoted differentiation of CD4+T-cells to Th2and Treg cells. The partial amelioration of these trends by allicin treatment could be mediated by STAT1and STAT6.2) LPDCs from wide type TH/S mice induced lower differentiation ratio of CD4+T cells towards Thl and Thl7especially under severe TH/S attack, in TLR5KO mice with or without TH/S the ability of LPDCs of inducing differentiation ratio of CD4+T cells towards Thl and Th17was low, which likely mediated by the ability of RA production. In wild type mice, TH/S can induce a higher ratio of citrobacter translocation to liver and blood. To our interesting, there is low ratio of citrobacter translocation in TLR5KO mice with or without TH/S.3) All six VRE strains isolated from stool samples caused severe enteritis. The same strains further inflicted significant damage and induced inflammatory reactions in Caco-2cells. Homologous assays demonstrated high homology between samples from stool and peripancreatic effusions in two patients, indicating the occurrence of extraenteric disseminations.Conclusion: T/HS resulted in less functionally mature gut associated DCs and significant DCsrelated immunosuppression, and the gut sourced pathogenic bacteria may causeinflammatory injuries to enteric epithelium during the course of TH/S, which resultingin enteritis and extraenteric disseminations.