Intraperitoneal immunity and pneumoperitoneum

Background: Carbon dioxide (CO2) pneumoperitoneum has been implicated as a possible factor in depressed intraperitoneal immunity. Using in vitro funct ional assays, CO2 has been shown to decrease the function of peritoneal mac rophages harvested from insufflated mice. However, an effective in vivo ass essment is lacking. Listeria monocytogenes (LM), an intracellular pathogen, has served as a well-established in vivo model to study cell-mediated immu ne responses in mice. This study examines the immune competence of mice bas ed on their ability to clear intraperitoneally administered LM following CO 2 vs helium (He) insufflation. Methods: Eighty-five mice (C57Bl/6, males, 4-6 weeks old) were divided betw een the following four treatment groups: CO2 insufflation, He insufflation, abdominal laparotomy (Lap), and control (anesthesia only). Immediately pos toperatively, each group was inoculated percutaneously and intraperitoneall y with a sublethal dose (.015 x 10(6) org) of virulent LM (EGD strain). Hal f of the animals were killed on postoperative day 3 and half on day 5. Sple ens and livers (sites of bacterial predilection) were harvested, homogenize d, and plated on TSB agar. The amount of bacteria (1 x 10(6) LM/spleen and liver) from each group was then compared. Statistical significance was set at p less than or equal to 0.05. Results: Control animals had nominal bacteria on day 3 (0.016 x 10(6) LM/sp leen and liver), and the bacterial burden remained low at day 5 (0.038 x 10 (6) LM/spleen and liver) postchallenge. On day 3, the bacterial burden was significantly higher in the CO2 group (5.46 x 10(6) LM/spleen and liver) as compared to He (0.093 x 10(6) LM/spleen and liver) and controls. The Lap g roup (3.44 x 10(6) LM/spleen and liver) had significantly more bacteria tha n the controls. There were no significant differences between any of the gr oups on day 5. Conclusions: In this animal model, CO2 pneumoperitoneum impaired cell-media ted intraperitoneal immunity significantly more than He pneumoperitoneum an d controls on day 3. Also on day 3, laparotomy caused impairment of intrape ritoneal immunity when compared to controls. Finally, intraperitoneal immun osuppression resolved by day 5.