Objective T Iymphocytes were considered to be activated and involved in the ischemia-reperfusion injury during lung transplantation.Carbon dioxide pneumoperitoneum was shown to have inhibitory activity on the immune system.This study was designed to_investigate the effects of the effects of the therapeutic hypercapnia on the T Iymphocytes of rats in which ischemia-reperfusion injury occurred during lung transplantation.Melhods Sixteen Wismr rats weighed 300 to 400 g were randomized into control group(8 rats) or therapeutic group (8 ras)after transplantaion.Animals in both grotups were Oven inluded nitrogen(50%)and oxygen N2+(50%) at baseline. Animats in the control groap were given irked nitrogen (50%)and oxygen(50%)throughout the experiment ,and that in the thera-peutic group were given mixed gas which was composed of nitroged(40%),oxygen(60%)and carbon dioxide in appropriate concentra-tion to keep arterial partial pressure of carbon dioxide (PaCO2)at 80-100 mm Hg and FiO2 at 50%after reperfusion.All of the ani-mals were observed for 90 minutes after reperfusion.Mean arterial pressure(MAP) and arterila partial pressure of oxygen(PaO2) were recorded at baseline and every 15 minutes during the period of reperfusion.The expression of CD3,CD4 and CD28 in the peripheral blood was,examined,and the concentrations of Ifn-у,IL-2,IL-4 and IL-1O in the homogenate were measured after the experiment. Histological analysis of samples from transplanted lungs was performed.Resykts After reoerfysion,MAP and PaO2 in the therapeutic group were higher signitleantly than that in the group(P