Red blood cells induce lung inflammation in hypoxia

Abstract

Red blood cells (RBCs) determine systemic vascular tone by releasing vasoactive factors. To determine RBC-induced lung responses, we inflated isolated, blood-perfused lungs of rat or mouse with normoxic or hypoxic gas. Corresponding blood pO2 were 150 and 33 mmHg. Using our reported methods (J. Clin. Invest. 2003. 111: –699), we quantified fluorescence in single endothelial cells (ECs) of lung capillaries by real-time fluorescence imaging. Using the dichloroluorescin (DCF) and fura 2 methods respectively, we detected EC ROS and EC cytosolic Ca2+ (Ca2+cyt) levels. In the presence of RBC-containing perfusion, hypoxic inflation increased both ROS and Ca2+cyt above baseline (P<0.05). However, both increases were blocked during RBC-free perfusion, or by inclusion of the H2O2 hydrolyzing agent, catalase in RBC-containing perfusion. The wild type hypoxic response caused leukocyte recruitment that was inhibited by separate infusions of RBC-free plasma, catalase, or of a blocking mAb against the leukocyte adhesion receptor, P-selectin (P<0.05). Perfusion with RBC from BERK-trait mice, in which hypoxia enhances RBC superoxide production, enhanced both hypoxia-induced EC ROS and the induced leukocyte recruitment (P<0.05). We conclude that in hypoxia, RBCs generate H2O2 that induces Ca2+-dependent EC P-selectin expression, leading to leukocyte recruitment, hence initiation of inflammation (HL69514).