摘要Objective:Xuebijing Injection(XBJI)is mainly used for treating sepsis in China,and even COVID-19 recently.This study aimed to clarify the molecular mechanism(s)and identify the potential"common culprit(s)"for XBJI-caused immediate hypersensitivity reaction(IHR)which is the main type of its adverse reactions.Methods:Antiserum against XBJI was prepared by intraperitoneal immunization in combination with aluminum adjuvant for five weeks.Antagonistic experiments were performed by using several antago-nists against different mediators in Evans Blue leakage model.Propranolol-pretreated mice were used to determine the capacity of XBJI to trigger systemic IHR.Serum total IgE(tIgE)and mouse mast cell pro-tease 1(MCPT-1)levels,complement activation,and the levels of supernatant inflammatory mediators were determined by ELISAs.Lipopolysaccharide(LPS)-activated RAW264.7 macrophages were used for evaluating the anti-inflammatory activity of XBJI,while human mast cells(LAD2)were used for assessing the effect of XBJI on mast cell degranulation.Results:Continuous treatment(i.p.)with XBJI along with aluminum adjuvant did not elevate the levels of serum tIgE and MCPT-1.In vitro,XBJI could not directly cause the degranulation of LAD2 cells.It induced a robust Evans Blue leakage after the first injection in mouse paw.Mechanism study demonstrated that antagonists for histamine H1/H2 receptors and complement C3a receptor counteracted XBJI-induced IHR.XBJI also directly activated complement C3 in human serum.Through screening five herbs of XBJI and the constituents,only safflower yellow(SY)in Carthami Flos was able to induce IHR.The discolored-XBJI not only did not induce IHR locally and systemically,but also could suppressing the pro-duction of proinflammatory mediators in LPS-activated RAW264.7 macrophages.Conclusion:XBJI failed to induce immune IHR,but potently triggered non-immune IHR through direct activating complement C3 to provoke histamine release.SY in Carthami Flos was the underlying"common culprit"responsible for XBJI-caused IHR.The anti-inflammatory action of XBJI can be retained after decol-orization.Our study provides a scientific basis for not only preventing and treating XBJI-caused IHR clin-ically,but also improving its production process.