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Patients with sickle cell anemia suffer from devastatingly painful episodes, called crises caused by sticky sickle red blood cells that get stuck in small blood vessels and obstruct blood flow. Scientists at the Lindsley F. Kimball Research Institute (LFKRI) of the New York Blood Center have identified a subset of white blood cells called patrolling monocytes which can remove the sickle blood cells attached to the cells of the vessel wall. The study which was published in the August issue of the journal Blood was selected as a Plenary paper and was the cover of the same issue. In the study, Dr. Yunfeng Liu, a LFKRI Research Fellow and colleagues found that patients with sickle cell anemia have reduced numbers of these patrolling monocyte and that during crisis the numbers are further decreased. Using experimental models of sickle cell anemia, the group went on to show that depletion of the patrolling monocytes exacerbated the clogging of the blood vessels by sickle red blood cells and caused cellular damage to the surrounding tissue whereas increasing the numbers of patrolling monocytes using drugs reduced the extent of blood vessel blockage. These findings highlight the therapeutic potential of modulating patrolling monocyte numbers either by using drugs or cellular therapy for prevention of pain crisis in patients with sickle cell anemia. Interestingly, transfusions bolstered the numbers of these patrolling monocytes, uncovering yet another beneficial effect of transfusions for patients with sickle cell anemia besides correcting the anemia and other sickle cell complications.

Liu Y, Zhong H, Bao W, Mendelson A, An X, Shi P, Chou ST, Manwani D, Yazdanbakhsh K. Patrolling monocytes scavenge endothelial adherent sickle RBC: a novel mechanism of inhibition of vaso-occlusion in SCD. Blood. 2019 Aug 15;134(7):579-590.​