Objective:To study the dynamic changes of cellular immune function in peripheral blood of trauma patients and its role in the evaluation of traumatic complications.Methods:A prospective cohort study design was conducted. Patients with blunt trauma admitted to Chongqing Emergency Medical Center from November 2019 to January 2020 were consecutively enrolled. The peripheral blood samples were collected at 1, 3, 5, 7, and 14 days after injury. The expressions of CD64, CD274, and CD279 on the surface of neutrophils, lymphocytes, and monocytes as well as CD3 +, CD4 + and CD8 + T lymphocyte subsets were measured by flow cytometry. The trauma patients were divided into different groups according to the injury severity score (ISS) and sepsis within 28 days after injury, respectively. The dynamic changes of cellular immune function in different time points after injury and differences between different groups were compared. Furthermore, the correlation with acute physiology and chronic health evaluation Ⅱ (APACHEⅡ), sequential organ failure assessment (SOFA), and ISS were evaluated by Pearson correlation analysis. Results:A total of 42 patients with trauma were finally enrolled, containing 8 severe trauma patients with ISS greater than 25 scores, 17 patients with ISS between 16 and 25 scores, and 17 patients with ISS less than 16 scores. The sepsis morbidity rates were 14.3% (n = 6) within 28 days after injury. CD64 index and CD4 +T lymphocyte subsets were significantly increased at different time points after trauma (H = 15.464, P = 0.004; F = 2.491, P = 0.035). The CD64 index and positive rates of CD279 in neutrophils, lymphocytes, and monocytes were increased with the severity of injury at day 1 and day 3 after injury, respectively. At the first day after injury, CD64 index were 2.81±1.79, 1.77±0.92, 3.49±1.09; positive rate of CD279 in neutrophils were 1.40% (0.32%, 2.04%), 0.95% (0.44%, 2.70%), 12.73% (3.00%, 25.20%); positive rate of CD279 in lymphocytes were 3.77% (3.04%, 5.15%), 4.71% (4.08%, 6.32%), 8.01% (4.59%, 11.59%); positive rate of CD279 in monocytes were 0.57% (0.24%, 1.09%), 0.85% (0.22%, 1.25%), 6.74% (2.61%, 18.94%) from mild to severe injury groups, respectively. The CD64 index in severe injury group was significantly higher than that in moderate group, and the positive rates of CD279 in neutrophils, lymphocytes and monocytes of severe injury patients were higher than those in other two groups (all P < 0.05). At 3rd day after injury, compared to moderate group, severe injury patients had significantly higher CD64 index and positive rate of CD279 in lymphocytes [4.58±2.41 vs. 2.43±1.68, 7.35% (5.90%, 12.28%) vs. 4.63% (3.26%, 6.06%), both P < 0.05]. Compared with the non-sepsis patients, the sepsis patients had significantly higher CD64 index and positive rate of CD279 in monocytes at day 1 after injury [4.06±1.72 vs. 2.36±1.31, 3.29% (1.14%, 12.84%) vs. 0.67% (0.25%, 1.48%), both P < 0.05], and positive rate of CD279 in lymphocytes significantly higher at 3rd day after injury [8.73% (7.52%, 15.82%) vs. 4.67% (3.82%, 6.21%), P < 0.05]. In addition, correlation analysis showed that positive rate of CD279 in lymphocytes was positively correlated with SOFA and ISS, respectively (r values were 0.533 and 0.394, both P < 0.05), positive rate of CD279 in monocytes was positively correlated with APACHEⅡ, SOFA and ISS scores, respectively (r values were 0.579, 0.452 and 0.490, all P < 0.01), positive rate of CD279 in neutrophils was positively correlated with APACHEⅡ and ISS, respectively (r values were 0.358 and 0.388, both P < 0.05). Conclusions:CD64 index and CD279 expression in neutrophils, lymphocytes, and monocytes are significantly related to the severity and prognosis of trauma. Dynamic monitoring the cellular immune function may be helpful for assessing the prognosis of trauma patients.