Red blood cells regulate eosinophil chemotaxis by scavenging RANTES secreted from endothelial cells

Background Eosinophils play a critical role in the pathogenesis of allergic diseases. CC chemokines, such as regulated on activation, normal, T cell expressed, and secreted (RANTES), are key regulators of eosinophil locomotion. Although eosinophils migrate from the bloodstream into tissues, mechanisms that generate a chemogradient across the endothelium remain to be fully elucidated. Objective We first examined the polar secretion of RANTES by endothelial cells. We also studied the functional scavenging effect of red blood cells (RBCs) on RANTES secreted into the intravascular side. Methods and results Endothelial cells were cultured in a transwell chamber with a membrane pore size of 0.45, 3.0, and 8.0 mum and stimulated with TNF-alpha, IL-1beta, or IFN-gamma from the apical or basolateral side for 16 h. The measurement of RANTES in the supernatant was performed by ELISA. We did not see any difference in the amount of RANTES secreted from the cytokine-stimulated endothelium between inner (intravascular side) and outer (extravascular side) wells separated by the 8.0-mum membrane, although apical polarization was observed with the 0.45-mum membrane. The addition of RBCs (hemoglobin (Hb): 0.5-15 g/dL) to the apical supernatant of TNF-alpha-stimulated endothelial cells reduced the RANTES level in a concentration-dependent manner. The treatment of supernatant on the intravascular side with RBCs significantly enhanced the migration of eosinophils. Conclusion RBCs possess a scavenging effect on intravascular RANTES, and thereby regulate transendothelial migration of eosinophils. Our findings suggest a new role of RBCs in allergic inflammation.