Abstract: Objective: To study the role of immune imbalance in patients with severe acute pancreatitis secondary to systemic infection. Methods: 55 cases of patients with severe acute pancreatitis was divided into secondary to systemic infection group (A group) and suspected systemic infection with or without systemic infection group (B group).Assayed the level of human leukocyte antigen DR (HLA-DR), T helper lymphocyte 1 / 2 (Th1 / Th2) ratio, the regulation of T cell (Treg) level in peripheral blood on the 1st, 3rd, 7th, 10th day. The mortality rate at 28 days and the length of stay in surgical intensive care unit(SICU)were recorded. Results: In 55 patients, length of SICU stay were(9.82± 4.32) days, length of hospital stay were (24.72±10.35)days, the mortality rate at 28 days was 9.09% (5 / 55). The mortality of Group A was higher than the B group .At each time point, the value of HLA-DR i n A group were significantly lower than B group. Two groups of the Th1 / Th2 value increased firstly, after reducing, at each time point in A group were significantly lower than B group. Two groups of Treg decreased, increased after, the A group were significantly higher than that of B group. All patients at each time point Th1 / Th2 value was closely related to Treg. Two groups of SICU stay stay, mortality significantly associated with HLA-DR%. The number of involved organ was closely related to HLA-DR and the mortality rate ,wich was significantly increased in group A, decreased in group B. Conclusion: The group of patients with systemic infection occurs early antigen presenting function hindrance, immune imbalance, increased body internally, exogenous susceptibility to infection, the body can not effectively remove pathogens ,appearing systemic infection, prolonged SICU stay days, increased the mortality rate.

Key words: Immune imbalance, Severe Acute Pancreatitis, Human Leukocyte Antigen DR (HLA-DR)