Objective: To investigate the value of co-stimulatory molecule CD86 in evaluating sepsis in emergency infected patients. Methods: Patients who were18 years or older and had infection or were clinically highly suspected of infection admitted to the emergency intensive care unit and wards of Renji Hospital (affiliated to Shanghai Jiaotong University School of Medicine) between September 2019 to September 2020 were prospectively observed. According to the Sepsis 3.0, patients were divided into a sepsis group and a non-sepsis group. We recorded the clinical data of all patients, and checked all their complete blood cell, peripheral blood mononuclear cell (PBMC) CD86 and HLA-DR expression level, C-reactive protein (CRP), procalcitonin (PCT), albumin (ALB), lactic acid (Lac), serum interleukin level and calculation of CRP/ALB ratio, neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), lymphocyte/monocyte cell ratio (LMR) within 24 hours of admission. We compared the differences of the above indicators between the groups, and then further use the Logistics regression model for multivariate analysis. Results: A total of 91 patients were enrolled: 49 sepsis patients (15 deaths, 30.6%), 42 non-sepsis patients (0 deaths). In the sepsis group, the levels of CD86%, Neutrophils (N), CRP/ALB, NLR, IL-6, IL-10, SIL-2R, CRP, PCT were significantly higher than in the non-sepsis group (P<0.05), while HLA-DR, LY (lymphocytes), PLT (Platelets), ALB and LMR were significantly lower in the sepsis group than in the non-sepsis group (P<0.05). Multivariate Logistics regression analysis established the CD86 model and HLA-DR model, and found that in the CD86 model, CD86 respiration rate (RR), LYand PCT were independent predictors for sepsis (P<0.05), and the OR values were 1.539 (1.148-2.064), 1.141 (1.009-1.290), 0.280 (0.097-0.811)and 1.036 (1.005-1.068), respectively. In the HLA-DR model, HLA-DR and LY were found to be independent predictors for sepsis (P<0.05), with OR values of 0.971 (0.953-0.988) and 0.290 (0.117-0.718). Finally, the CD86 model, HLA-DR model and APACHII score were analyzed by ROC curve, and the areas under the curve (AUC) were 0.870 (0.796-0.944), 0.793 (0.700-0.887), 0.754 (0.653-0.855), respectively. Conclusion: The CD86 of PBMC in sepsis patients is increased, and HLA-DR is decreased. CD86 and HLA-DR can be used as early predictors for the occurrence of emergency sepsis. [ABSTRACT FROM AUTHOR]