Abstract: Objective To study the expression levels of annexin A1 (ANXA1), GATA-3, and T-bet in T lymphocytes of peripheral blood in burned mice with sepsis at early stage, and to analyze their immune regulatory mechanisms. Methods Seven-hundred and eighty male mice of clean grade were divided into sham injury group (n=60, sham injured on the back by immersing in 37 ℃ warm water for 10 s), burn group (n=240, inflicted with 20% TBSA deep partial- thickness burn on the back by immersing in 100 ℃ hot water for 10 s), sepsis group (n=240, intraperitoneally injected with 6 mg/kg lipopolysaccharide), and burn+ sepsis group (n=240) according to the random number table. Mice of burn+ sepsis group were treated as that in burn group at first, and then they were treated as that in sepsis group. (1) Immediately after injury, six mice in sham injury group were selected to collect lymphocyte suspension of peripheral blood (1 tube each mouse) according to the random number table. According to the random number table, 6 mice of each of the other three groups were respectively selected at post injury hour (PIH) 12, 24, 48, and 72 for the collection of lymphocyte suspension from peripheral blood (1 tube each mouse). Each tube of cell suspension was equally divided into two parts. Fluorescein isothiocyanate (FITC)-labeled human anti-mouse CD4 monoclonal antibody and phycoerythrin (PE)-labeled human anti-mouse interferon-γ monoclonal antibody were added to one part of cell suspension to mark helper T lymphocyte 1 (Th1). FITC-labeled human anti-mouse CD4 monoclonal antibody and PE-labeled human anti-mouse interleukin-4 (IL-4) monoclonal antibody were added to the other part of cell suspension to mark Th2. The percentages of Th1 and Th2 were determined with flow cytometer, and the ratio of Th1 to Th2 was calculated. (2) According to the random number table, 18 mice in sham injury group were selected immediately after injury for the collection of lymphocyte suspension of peripheral blood (1 tube each mouse), and 18 mice of each of the other 3 groups were respectively selected at PIH 12, 24, 48, and 72 to collect the lymphocyte suspension of peripheral blood (1 tube each mouse). The mRNA expression levels of ANXA1, GATA-3, and T-bet were determined by real-time fluorescent quantitative reverse transcription-PCR. (3) Immediately after injury, 36 mice in sham injury group were selected to collect lymphocyte suspension of peripheral blood (1 tube each mouse) according to the random number table, and then 36 tubes of cell suspension were divided into 6 batches (6 tubes each batch). Each one of 6 kinds of antibody combinations: antibodies for labeling Th1 and Th2 in combination with PE-anthocyanin 7 labeled human anti-mouse ANXA1 monoclonal antibody, PE-anthocyanin 7 labeled human anti-mouse GATA-3 monoclonal antibody, and PE-anthocyanin 7 labeled human anti-mouse T-bet monoclonal antibody was added to 1 tube of cell suspension at each batch. According to the random number table, 36 mice of each of the other 3 groups were respectively selected at PIH 12, 24, 48, and 72 for the collection of lymphocyte suspension of peripheral blood (1 tube each mouse), and then 36 tubes of cell suspension at each time point were divided into 6 batches for marking with 3 kinds of surface markers of Th1 and Th2 (6 tubes each batch). Each one of above-mentioned 6 kinds of antibodies was added to 1 tube of cell suspension at each time point for each batch. The percentages of ANXA1, GATA-3, and T-bet positive cells in Th1 and Th2 were determined with flow cytometer. Data were processed with one-way analysis of variance, analysis of variance of factorial design, and SNK test. The relationship between the percentages of ANXA1 positive cell and the percentages of GATA-3 positive cell in Th1 and Th2, and mRNA expression level of ANXA1 and mRNA expression level of GATA-3 in lymphocytes were assessed by linear correlation analysis. Results (1) Compared with those in sham injury group immediately after injury, the percentages of Th1 and Th2 and the ratio of Th1 to Th2 of mice in burn group were significantly decreased from PIH 24 on, with P values below 0.05; the percentages of Th1 and Th2 and the ratios of Th1 to Th2 of mice in sepsis group and burn+ sepsis group were significantly decreased from PIH 12 on, with P values below 0.05. (2) Compared with those in sham injury group immediately after injury, the mRNA expression levels of ANXA1 and GATA-3 in lymphocyte of mice in burn group were significantly decreased from PIH 24 on, with P values below 0.05; the mRNA expression level of T-bet was significantly decreased at PIH 24 but significantly increased at PIH 48 and 72, with P values below 0.05. Compared with those in sham injury group immediately after injury, the mRNA expression levels of ANXA1 and GATA-3 in lymphocytes of mice in sepsis group were significantly decreased from PIH 12 on, and the mRNA expression level of T-bet was increased significantly from PIH 12 on, with P values below 0.05; the mRNA expression levels of ANXA1, GATA-3, and T-bet in lymphocytes of mice in burn+ sepsis group were significantly decreased from PIH 12 on, with P values below 0.05, reaching the nadir at PIH 72 (0.50±0.04, 0.45±0.03, 0.21±0.05, respectively). (3) A significant positive correlation was observed between ANXA1 mRNA expression level and GATA-3 mRNA expression level in lymphocytes of peripheral blood (r=0.862, P<0.05). (4) Compared with those in sham injury group immediately after injury, the percentages of ANXA1 and GATA-3 positive cellsin Th1 and Th2 of mice in burn group were significantly lowered from PIH 24 on, and the percentage of T-bet positive cells was significantly decreased at PIH 24, but it was increased from PIH 48 on, with P values below 0.05. The percentages of ANXA1 and GATA-3 positive cells in Th1 and Th2 of mice in sepsis group were continuously decreased from PIH 12 on, which were lower at most time points than those in sham injury group immediately after injury, with P values below 0.05. The percentages of T-bet positive cells in Th1 and Th2 of mice in sepsis group were significantly increased since PIH 12 as compared with those in sham injury group immediately after injury, with P values below 0.05. The percentages of ANXA1, GATA-3, and T-bet positive cells in Th1 and Th2 of mice in burn+ sepsis group were continuously lowered from PIH 12, with significantly statistical differences at most time points as compared with those in sham injury group immediately after injury, with P values below 0.05. (5) The percentages of GATA-3 positive cells in Th1 and Th2 were significantly positively correlated with those of ANXA1 (with r values respectively 0.747 and 0.787, P values below 0.05). Conclusions The expression levels of ANXA1, GATA-3, and T-bet were continuously lowered in burned mice with sepsis, and it may play an important role in Th1/Th2 balance switching to Th2 bias and immunosuppressive process.