Abstract: Objectives To examine sICAM-1 in Pneumocystis carinii pneumonia (PCP) and the effect of TMP-SMZ therapy on its level and on pathological and immunological changes in rats. Methods 50 female Wistar rats were randomly divided into normal group (N group), PCP model group (PCP group) and TMP-SMZ therapy group (SMZ group). 1 mg of dexamethasone was injected intramuscularly twice a week for rats in PCP and SMZ groups to induce PCP. Normal saline was injected for N group in the same way. When the infection was confirmed, TMP-SMZ was given to rats in SMZ group by 25 mg/(kg.d) for 5 days for 3 courses with an interval of 2 weeks. sICAM-1 in serum was detected by ELISA, and the pathological changes in lungs and liver and the Pc in alveoli of lungs were observed. Results The level of sICAM-1 in PCP and SMZ groups at the 3rd week [(1.847±0.50) ng/ml，(1.787±0.59) ng/ml] was lower notably than that at 0 week[（2.407±0.81) ng/ml， [(2.478±0.59) ng/ml respectively](P<0.05), and then increased gradually. It was significantly higher in PCP group at 9th week[（3.233±0.83) ng/ml] and at 12th week[（3.984±0.87) ng/ml] than that of 0 week (P<0.05). Its level in SMZ group at 12th week[（3.621±1.62) ng/ml] was also higher than that in 0 week [（2.478±0.59) ng/ml] (P<0.05). sICAM-1 level in both PCP and SMZ groups at 9th week and 12th week was higher than that of N group (P<0.05，P<0.01). There was no significant difference between SMZ and PCP groups at 9th week and 12th week (P>0.05). Conclusion The sICAM-1 level in rats was low but significantly increases after the induction of PCP.

Key words: Pneumocystis carinii, Rat, Soluble intercellular adhesion molecule-1（sICAM-1）, Histopathology