Platelet and leucocyte activation in childhood sickle cell disease: association with nocturnal hypoxaemia

We hypothesized that vaso-occlusive events in childhood sickle cell disease (SCD) may relate to inflammatory cell activation as well as interactions b etween sickle erythrocytes and vascular endothelium. Peripheral blood was e xamined from 24 children with SCD, of whom 12 had neurological sequelae and seven had frequent painful crises, and 10 control subjects. Platelet (CD62 P and CD40L expression) and granulocyte (CD11b expression) activation and l evels of platelet-erythrocyte and platelet-granulocyte complexes were deter mined by flow cytometry. Platelets (P = 0.019), neutrophils (P = 0.02) and monocytes (P = 0.001) were more activated and there were increased platelet -erythrocyte complexes (P = 0.026) in SCD patients compared with controls. Platelet-granulocyte complexes were not raised. There were no differences b etween the different groups of SCD. As hypoxia activates monocytes, platele ts and endothelial cells and causes sickling of SCD erythrocytes, we also i nvestigated 20 SCD patients with overnight pulse oximetry. Minimum overnigh t saturation correlated with the level of platelet-erythrocyte complexes (S pearman's rho -0.668, P < 0.02), neutrophil CD11b (Spearman's rho -0.466, P = 0.038) and monocyte CD11b (Spearman's rho -0.652, P = 0.002). These find ings provide important clues about the mechanism by which SCD patients may become predisposed to vaso-occlusive events.