The Study Of Regulatory B Cells And Their Immunoregulatory Function In Sepsis Mice

BACKGROUND:Sepsis is caused by the immune responses triggered by infection factors,which always accompanied with systemic inflammatory response syndrome(SIRS).The pathology of sepsis depends on a combination of factors,such as the invading pathogens,the status of the immune system of the host,etc.Sepsis is a serious disease on clinic,with severe symptoms and high mortality.The pathogenic mechanism of sepsis is not clarified at present and there are no effective clinical therapies yet.Some researches reported that the survival of bacterial infection induced sepsis in mice decreased in B-cell-deficient mice.This reminds us,there might be a B cell subset which could suppress the infectous induced immune reactions to protect sepsis mice.Certain B cells can suppress immune responses,which termed "Regulatory B cell(Breg)".According to current researches,there are multiple B cell subsets being described as "Breg".Among these subsets,CD5+CD1dhi Breg as one of the earliest discovered immunosuppressive B cells.Breg subset plays a regulatory role in the development of a variety of diseases,such as autoimmune diseases,infection and tumor,etc.While the relationship between Breg and sepsis has not been well characterized yet and there is still no report about CD5+CD1dhi Breg in sepsis.OBJECTIVE:This study is to investigate the involvements of immunosuppressive CD5+CD1dhi Breg subset in sepsis mice and to see whether splenic CD5+CD1dhi Breg could protect mice from sepsis.This will help us to clarify the pathogenesis of sepsis and improve the treatment of sepsis.METHODS:We established different severity of sepsis models by intraperitoneal injection of different doses of lipopolysccharide(LPS)or using cecum ligation puncture(CLP).IFN-? in peripheral blood was detected by ELISA.The changes of splenic CD5+CD1dhi Breg and function-related molecules,including CD25,CD86,FasL and IL-10,etc,in splenocytes or CD19+B cells were measured by Flow cytometry.The suppressive function of CD5+CD1dhi Breg in sepsis mice and control mice were judged by the suppressive effect indicated by inhibiting the proliferation of CD4+T cells.Then adoptive transfer of CD5+CD1dhi Breg to sepsis mice were executed to observe whether IL-10 producing Breg could alleviate sepsis.RESULTS:1.Splenic CD5+CDldhi Breg number reduced in sepsis mice;2.The expression of CD25,CD86 and FasL in splenic CD5+CD1dhi Breg subset increased in LPS-induced sepsis mice,which indicated the activation of Breg;3.The secretion of IL-10 by splenic CD5+CD1dhi Breg decreased in severe sepsis mice but increased in moderate sepsis mice;4.The suppressive function of splenic CD5+CD1dhi Breg weakened in LPS-induced severe sepsis mice;5.Adoptive transfer of activated splenic CD5+CD1dhi Breg alleviated sepsis and prolonged the survival of LPS-induced sepsis in miceCONCLUSIONS:The number and immune suppressive function of splenic CD5+CD1dhi Breg decreased in severe sepsis;the defect immunoregulatory function of CD5+CD1dhi Breg might due to the reduction of IL-10 production after activation in this Breg subset and attribute to the rapid death in severe sepsis mice compared with moderate sepsis mice.IL-10 producing CD5+CD1dhi Breg could protect sepsis by prolonged survival time.These results indicated their important involvement of IL-10 producing Breg subset in the pathogenesis and treatments of sepsis.