Investigation On The Mechanism Of AIM Induced Immune-Modulation In Sepsis

Objective Sepsis,characterized by failed host defense which leads to multiple organ dysfunctions,is the major cause of death in patients with infection.About 14000 people die from sepsis every day,leading to more deaths than AIDS,breast cancer and prostate cancer combined.The pathogenesis of sepsis includes early infection and imbalance of host response.However,the factors involved in disturbing host homeostasis during sepsis are largely unknown.Apoptosis inhibitor of macrophage(AIM/CD5L)is a novel immunoregulatory molecule belonging to scavenger receptor cysteine-rich(SRCR)domain superfamily.Recently,it's found that AIM is mainly produced by tissue macrophages and exists in the form of free and binding AIM in peripheral blood.AIM in the form of compounds bounding to IgM is not easy to be cleared by kidneys,which keeps AIM at a high level in peripheral blood(~10?g/ml).Many studies have found that AIM,as a new type of pattern recognition receptor,can recognize bacterial and fungal components,inhibit the release of inflammatory factors such as TNF-? and regulate the function of macrophages,thus playing a key role in inflammatory response.However,whether AIM participates in multiple organ damage caused by immune disorders in sepsis remains to be elucidated.This study aims to determine the immunopathological role of apoptosis inhibitor of macrophage AIM in sepsis by detecting the expression of AIM in septic patients and mice,and observing the effects of AIM blockade in septic mice model.Methods Pathogen-free 6 to 8-week-old female C57BL/6 mice were anesthetized with a mixture of xylazine(4.5 mg/kg)and ketamine(90mg/kg)intraperitoneally,and cecal ligation puncture(CLP)was used as a model of systemic sepsis syndrome.The expression of AIM in peripheral blood,peritoneal lavage fluid(PLF),liver,spleen,lung and kidney of septic mice was detected by ELISA.The immune regulatory role of AIM in sepsis was evaluated by survival rate test,bacterial load test,multi-organ histopathological score and organ damage marker evaluation.The specific molecular mechanisms of AIM induced immune-modulation in sepsis was explored by flow cytometry,factor screening,and in vitro cell culture.Results We showed that blockade of AIM led to significantly increased survival after experimental sepsis,and it decreased local and systemic inflammation,reduced tissue injury,and inhibited bacterial dissemination in the blood,in particular at later time points.Supplementation of recombinant AIM in sepsis resulted in increased tissue injury,amplified inflammation,increased bacteremia,and worsenedmortality.Interestingly,the most important difference in the production of cytokines and chemokines after in vivo AIM blockade or AIM administration during sepsis was IL-10.In vitro,AIM enhanced IL-10 production from macrophages,neutrophils,or lymphocytes.In vivo,the beneficial effects of AIM blockade and the detrimental effects of AIM addition on experimental sepsis were ablated by treatment with recombinant IL-10 and neutralizing anti–IL-10 antibodies,respectively.Conclusion AIM may play an immunological role in sepsis by participating in the process of bacterial clearance and inflammation regulation.In the early phage of sepsis,AIM is highly expressed and acts on natural immune cells.On the one hand,the release of pro-inflammatory factors directly aggravate multiple organs injury.On the other hand,AIM induces the release of anti-inflammatory factor IL-10,leading to immune suppression and impairs the ability of bacterial clearance.Thus,the proliferation of bacteria further aggravates the immune disorder of inflammation,resulting in a vicious circle,leading to the death of sepsis.This study is the first to identify AIM as an important mediator in disturbing host homeostasis in sepsis.