Phenotypic commitment of monocytes towards a protective hemoglobin scavenging phenotype (CD14posCD163highHLA-DR low) following cardiopulmonary bypass

Abstract

Background: Intravascular hemolysis may cause tissue injury directly or via a systemic inflammatory response. Under physiological conditions, extracorpuscular hemoglobin (Hb) is bound by haptoglobin (Hp) and the complex internalized via the hemoglobin scavenger receptor CD163 on monocytes, prior to catabolism via heme-oxygenase-1 (HO-1). Recently, a novel subset of CD68 posCD163highHLA-DRlow macrophages with high expression of HO-1 was recognized in hemorrhagic areas of atherosclerotic plaques, distinct from CD68posCD163lowHLA-DR high foam cell macrophages with low- HO-1 content. Considering the hemolytic insult during CPB, we hypothesized that an equivalent compensatory CD163highHLA-DRlow phenotype will evolve in circulating CD14pos monocytes post surgery. Methods: Twelve patients undergoing elective surgery with CPB were enrolled with informed consent. Whole-blood samples were collected in EDTA at predetermined time-points, pre- intra-, and postoperatively. Whole-blood was evaluated by three-color flow cytometry for expression of CD14, CD163, and HLA-DR; CD14pos cells were also permeabilized to detect intracellular HO-1 protein. Plasma [Hp-Hb] concentration was determined by ELISA. Results: A striking phenotypic switch from CD163 lowHLA-DRhigh preoperatively to CD163highHLA- DRlow postoperatively at 24 h was observed on circulating CD14 pos monocytes. Intracellular HO-1 protein was also significantly up-regulated at 24 h after declamping. These phenotypic changes were preceded by peak Hb-Hp levels observed at 2 h. Conclusion: We have shown for the first time, a phenotypic commitment of monocytes towards a protective CD14 posCD163highHLA-DRlow population with increased intracellular HO-1 occurring in the circulation during the recovery phase of CPB. These findings have implications for monitoring of antiinflammatory interventions and linkage to clinical outcomes. © 2010 International Clinical Cytometry Society.