Abstract： Objective To investigate the role expression of interleukin 22(IL-22) and its receptor,IL-10R2, in pneumonia rats infected with Klebsiella pneumonia. Methods Fifty specific pathogen free SD rats were randomized into the pneumonia group and the control group (n=25 each). The rats in the pneumonia group received intratracheal injection of Klebsiella pneumoniae for establishment of infection model, while those in the control group were injected with equal volume of sterile normal saline. At 4 h, 1,2, 3 and 4 days later, the rats were studied for general conditions, gross and microscopic pathology of the lung tissue, and bacterial colony counts to validate the pneumonia model. At 4 h, 1, 2, 3 and 4 days after modeling, the expression of IL- 10R2 mRNA in lung tissues was determined by real- time fluorescent quantitative PCR and circulating IL-22 examined by ELISA. Linear regression was used to analyze the correlation between colony counts and the expression of IL-22 and its receptor. Results At 4 h after modeling, the pneumonia rars experienced physical inactivity, gathering and pilomotor reflex. The lung tissues appeared grossly congestive and edematous. Under microscopy, destruction of alveoli, remarkable congestion and edema of alveolar space and pulmonary interstitial tissue, and massive neutrophilic infiltration were found. Bacterial culture was positive for lung tissue in pneumonia rats. The bacterial colony count was the highest at 4 h[(0.94±0.02) × 105 CFU/g]and then declined to the nadir on day 4[(0.07±0.00)×105 CFU/g], which indicated successful modeling. Compared with the control group, IL-10R2 mRNA expression in the pneumonia model group began to increase at 4 h, peaked on day 3 (12.95±0.65 vs 0.31± 0.31, P＜0.05), and then declined afterwards. At any given time point, the level of circulating IL-22 was lower in pneumonia group than that in control group. Moreover, the level of circulating IL-22 in pneumonia group started to increase obviously on day 3 as compared to 4 h post-modeling, and then continued to rise with time. At any given time points, the expression of lung tissue IL-10R2 mRNA and the circulating IL-22 were negatively correlated with bacterial colony counts of the lung (r=-0.64, P=0.01 ; r=-0.59, P=0.00).Conclusions IL-22 receptor IL- 10R2 mRNA is highly expressed in pneumonia with Klebsiella pneumoniae.The peripheral blood IL-22 may be depleted during infection but may also recover as the pneumonia is improving. IL-22 is the early inflammatory factor in infection with Klebsiella pneumoniae, and has a role in bacterial eradication in vivo.