The Immune Regulatory Function And Mechanism Of Mannan-binding Lectin In Fulminant Hepatitis

Fulminant hepatitis(FH)is a serious liver disease characterized by rapid deterioration of hepatic functions,massive hepatocyte necrosis and loss of liver structure.It can be secondary to viruses,drugs and metabolic diseases.Acute liver failure is associated with serious metabolic disorders.The hypercatabolism is associated with release of inflammatory cytokines and catabolic products in the systemic circulation,which can worsen patients’ clinical conditions.Activation of immune cells and their subsequent production of inflammatory cytokines such as TNFα,IL-1β and IL-6 can affect the course of fulminant hepatitis.Activation of immune cells can undergo metabolic reprogramming.For example,metabolism of activated macrophage can be converted from oxidative phosphorylation to aerobic glycolysis,which in turn mediates the release of inflammatory cytokines.Mannan-binding lectin(MBL)is a key molecule in immunity.It is mainly synthesized by liver cells and secreted into the blood.As a pattern recognition molecule,MBL can recognize carbohydrates on the surface of pathogens and activate the complement cascade to exert anti-infective effects.It has been reported that MBL is closely related to various liver diseases such as hepatitis,liver failure and liver cancer and so on.The serum levels and gene mutations of MBL are related to fulminant hepatitis caused by hepatitis B virus.Hepatitis B virus is an important reason for serious hepatitis in China.But the role of MBL in virus-induced fulminant hepatitis and its regulatory mechanisms are unknown.We found that in the model of fulminant hepatitis induced by mouse hepatitis virus A59(MHV-A59)or polyinosine-polycytidylic(polyI:C)and D-Galactosamine(D-GalN),MBL deficient mice compared with WT,had more serious liver damage,a higher proportion of tunel-staining cells,increased neutrophils and macrophages.The level of TNFα,IL-1β and IL-6 were also increased.It suggested that MBL may play a protective role in virus-induced fulminant hepatitis.NOD-like receptor 3 is a danger signal sensor,which can activate Caspasel and mediate the production of inflammatory cytokines such as IL-1β and IL-18.NLRP3 is also reported as an important molecule in fulminant hepatitis.Metabolic reprogramming in immune cell plays an important role in the various diseases.It has been reported that pyruvate kinase M2 can regulate the metabolism and inflammation.It can activate the NLRP3,an inflammasome which can mature Pro-IL-1β into IL-1β.Therefore,we further tested the level of PKM2 and the activation of NLRP3,We found that compared with WT mice,the expression of PKM2 and NLRP3 activation related proteins were increased in MBL deficient mice.Immunofluorescence analysis showed that macrophage expressed the PKM2 and its expression was increased in MBL deficient mice than WT.It suggested that macrophage played an important role in fulminant hepatitis.We used the PKM2 inhibitor shikonin to verify our results.It showed that the activation of NLRP3 were down-regulated,and the difference between the two groups of mice disappeared after using inhibitor.The bone marrow-derived macrophages were isolated from WT and MBL deficient mice and stimulated with polyI:C in vitro.It displayed that the expression of PKM2 and activation of NLRP3 were increased in cells isolated from MBL deficient mice than WT.The activation of NLRP3 was down-regulated and the differences between the two groups disappeared after using inhibitor of PKM2.In summary,MBL may reduce the activation of NLRP3 and the release of IL-1βin virus-induced fulminant hepatitis through down-regulating PKM2.The results may provide new ideas and basis for clinical drug guidance for those MBL gene deletion or low expression patients with fulminant hepatitis.