Targeting Mac-1-mediated leukocyte–RBC interactions uncouples the benefits for acute vaso-occlusion and chronic organ damage

Vaso-occlusive crisis (VOC) is one of the most common complications of sickle cell disease (SCD). Recurrent episodes of VOC may cause irreversible organ damage and early mortality in patients with SCD. Emerging evidence suggests that VOC arises from a complex cascade that involves interactions among multiple blood and endothelial cells in the vasculature. Previous studies have identified α_Mβ₂ integrin (Mac-1) as a critical molecule that mediates heterotypic interactions between red blood cells (RBCs) and adherent leukocytes and promotes VOC in SCD mice. Here, we show that RBC–leukocyte interactions are significantly diminished in Mac-1-deficient SCD mice, leading to an improvement of blood flow rates and prolonged survival time in a tumor necrosis factor-alpha and surgical-trauma-induced VOC model. Mac-1-deletion, however, was not sufficient to reduce SCD-related chronic organ damage. Our results thus suggest uncoupled mechanisms between acute VOC benefits and the long-term complications of SCD that should be considered in future clinical trials.