Patrolling Monocytes Scavenge Endothelial Adherent Sickle Red Blood Cells in Sickle Cell Disease

Sickle cell disease (SCD) is characterized by hemolytic anemia and increased entrapment of sickle red blood cells (RBCs) via attachment to the underlying activated vascular endothelium, resulting in vaso-occlusive crisis (VOC), marked by severe pain. The endothelial scavenging patrolling monocytes (PMos) expressing high levels of the heme oxygenase 1 (HO-1), a heme degrading enzyme, were recently shown to protect against vaso-occlusion in SCD, although their ability to scavenge endothelial-attached sickle RBCs was not tested. Here, we found that circulating PMos from SCD patients showed roughly 5% ± 0.5% engulfed GPA+ or Band3+ RBC specific material as compared to 0.7% ± 0.04% in healthy donor (HD) PMos or 0.85% ± 0.07% in SCD classical monocytes (CMos) as detected by flow as well as imagining flow cytometry, suggesting that PMos uptake RBCs in SCD. To further investigate this, RBCs purified from HDs (to mimic transfused cells) or SCD patients were labelled with CFSE, and co-cultured with purified monocytes without or with human microvascular endothelial cells (HMVEC). We found 11% ± 0.5% CFSE+ PMos in co-cultures with SCD RBCs in presence of HMVEC as compared to 2.7% ± 0.4% when cultured with HD RBCs, indicating that PMos engulf sickle RBCs, but not HD RBCs. Low levels of CFSE+ PMos (2-3%) were detected in cocultures with either sickle or control RBCs in the absence of HMVEC, implicating that PMos preferentially uptake endothelial cell (EC)...
Source: Blood - Category: Hematology Authors: Tags: 401. Basic Science and Clinical Practice in Blood Transfusion: Basic Science Source Type: research