Time course of differences in lymphocyte proliferation rates after laparotomy vs CO₂ insufflation

Background: Our laboratory has previously demonstrated that cell- mediated immune function is significantly more suppressed after both laparotomy and laparoscopic-assisted bowel resection than after peritoneal insufflation or open bowel resection, as assessed by delayed-type hypersensitivity (DTH) response. The purpose of this study was to further evaluate cell-mediated immunity by examining lymphocyte proliferation rates after laparotomy vs CO₂ insufflation. Methods: Female Balb/C mice (n = 75) were randomly divided into the following three groups: (a) anesthesia control (A/C), (b) CO₂ insufflation (INS), and (c) sham laparotomy (OPEN). The A/C group mice underwent no procedure. The INS group underwent insufflation with CO₂ gas at 4-6 mmHg for 20 min. The OPEN group underwent a midline incision from xiphoid to pubic symphysis, which was clipped closed after 20 min. Splenocytes were obtained via splenic harvest and lymphocyte isolation on postoperative days (POD) 1, 2, 3, 4, and 8. Lymphocyte proliferation was determined by a nonradioactive colorimetric MTS/PMS assay 72 h after concanavalin A stimulation. Results: The laparotomy group's lymphocyte proliferation rates were significantly lower than both the control and the insufflation groups on POD 2, POD 3, and POD 4. On POD 1 and POD 8, there were no significant differences in lymphocyte proliferation among the three groups. No differences were found between the control and insufflation groups at any point. Conclusions: After stimulation, lymphocytes proliferate at a lower rate after laparotomy than after CO₂ insufflation. Significant differences in lymphocyte proliferation rates between groups persist at least through POD 4. By POD 8, the mean lymphocyte proliferation rate in the laparotomy group was back to the baseline level. Our results suggest greater immunosuppression after sham laparotomy than after CO₂ insufflation.