Carbon Dioxide Sensing by Immune Cells Occurs through Carbonic Anhydrase 2–Dependent Changes in Intracellular pH

Abstract

CO 2 , the primary gaseous product of respiration, is a major physiologic gas, the biology of which is poorly understood. Elevated CO 2 is a feature of the microenvironment in multiple inflammatory diseases that suppresses immune cell activity. However, little is known about the CO 2 -sensing mechanisms and downstream pathways involved. We found that elevated CO 2 correlates with reduced monocyte and macrophage migration in patients undergoing gastrointestinal surgery and that elevated CO 2 reduces migration in vitro. Mechanistically, CO 2 reduces autocrine inflammatory gene expression, thereby inhibiting macrophage activation in a manner dependent on decreased intracellular pH. Pharmacologic or genetic inhibition of carbonic anhydrases (CAs) uncouples a CO 2 -elicited intracellular pH response and attenuates CO 2 sensitivity in immune cells. Conversely, CRISPRdriven upregulation of the isoenzyme CA2 confers CO 2 sensitivity in nonimmune cells. Of interest, we found that patients with chronic lung diseases associated with elevated systemic CO 2 (hypercapnia) display a greater risk of developing anastomotic leakage following gastrointestinal surgery, indicating impaired wound healing. Furthermore, low intraoperative pH levels in these patients correlate with reduced intestinal macrophage infiltration. In conclusion, CO 2 is an immunomodulatory gas sensed by immune cells through a CA2-coupled change in intracellular pH.

Hypercapnia alters mitochondrial gene expression and acylcarnitine production in monocytes

“…Given that monocyte infiltration, M2 macrophage polarization and hypercapnia are co-incident in COPD, our data provide novel insights into the immunometabolic landscape of hypercapnic lung disease. Hypercapnia and acidosis have previously been reported to attenuate M1 macrophage differentiation and migration, 46 which is indicative of an attenuated inflammatory immune response. Here we build on these studies to demonstrate that CO 2 per se causes a marked immunometabolic shift in monocytes and macrophages that further attenuates proinflammatory signaling.…”

“…In addition, THP‐1 cells respond to LPS 49–51 stimulation and differentiated THP‐1 macrophages have shown an altered immune response to elevated CO 2. 28,46,52 We have recently extensively characterized the shNT version of these cells described by Phelan et al 20 . where monocytes have been stably transduced with a nontarget short hairpin RNA.…”

“…After lysing of erythrocytes and repeated centrifugation, cells were resuspended in Roswell Park Memorial Institute 1640 (Merck) with 10% fetal calf serum, 1% penicillin–streptomycin, 2 m m L‐glutamine and 10 ng mL −1 macrophage colony–stimulating factor. Pooled cells of one mouse were seeded in one T‐75 flask (660175‐120G; Greiner Bio‐One International, Frickenhausen, Germany) and split after 48 h. After 7 days in culture, cells were harvested and identified by F4/80 immunostaining as described previously. 46 …”

“…For most THP‐1 experiments, cells were used at a density of 750 000 cells mL −1 of media. We have recently demonstrated that intracellular pH does not change significantly in Phorbol 12‐myristate 13‐acetate (PMA)‐treated THP‐1s cultured under these buffered hypercapnia conditions 46 . Representative media pH, pCO 2 and pO 2 measurements are included in Supplementary table 1.…”

Laparoscopic-Assisted Colorectal Resection Can Reduce the Inhibition of Immune Function Compared with Conventional Open Surgery: A Retrospective Clinical Study

“…The application of pneumoperitoneum requires the introduction of large amounts of CO 2 gas into the abdominal cavity, and studies have shown that CO 2 pneumoperitoneum may produce hypercapnia and have immunological effects on the body [ 24 ]. Kim I. and his colleague reported that low intra-abdominal pressure during laparoscopic colorectal surgery, which means less CO 2 , preserved innated immune homeostasis and formed a valuable addition to future enhanced recovery [ 25 ].…”