Acidification enhances peritoneal macrophage phagocytic activity

BACKGROUND: Laparoscopic surgery is currently used in an array of diverse clinical situations, including cases with potential bacterial contamination. Previous studies have shown that CO2 insufflation during laparoscopic procedures modulates the immune response due to the acidification of the peritoneum. In the present study, we investigated whether exposure of macrophages to an acidic environment, such as that produced by CO2 insufflation, could affect phagocytosis, which is the fundamental process for bacterial clearance. MATERIALS AND METHODS: A murine peritoneal macrophage line (J774) was pre-incubated at pH levels of 6.0 or 7.4 for 3 h at 37 degrees C and returned to neutral pH (7.4). Phagocytosis was evaluated by incubation with fluorescein isothiocyanate-conjugated IgG-opsonized bacterial particles, IgG-opsonized fluorescent latex beads, and non-opsonized fluorescent latex beads at 37 degrees C, pH 7.4. The intensity of the internalized signal was measured by using a fluorometer. RESULTS: Pre-incubation of macrophages at a pH of 6.0 resulted in a significant increase of phagocytic activity of opsonized particles. However, it did not change the uptake of non-opsonized particles. This effect was due to the internalization process since there were no differences in foreign particle binding of cells exposed to acidic or neutral pH levels. CONCLUSIONS: This study demonstrates that environmental acidification increases the phagocytosis of opsonized particles by macrophages. These results suggest that CO2 insufflation during laparoscopic surgery may be beneficial for the clearance of pathogens, particularly in cases where there is a high risk of potential intra-abdominal infections.