Because blood transfusion is routinely given to patients with normal or high fibrinogen level, the transfusion of stored red cells has the potential to induce increased aggregation in vivo, depending on the storage period. This should be taken into account when blood transfusion is considered, particularly for patients with microcirculatory disorders.

Summary. The adherence of red blood cells (RBC) to endothelial cells (EC), shown to correlate with microvascular occlusion in sickle cell disease and malaria, is considered a major contributor to microcirculatory disorders. In the present study the adherence to EC was markedly enhanced with RBC from b-thalassaemia major (TM) patients, and even more so with RBC from b-thalassaemia intermedia (TI) patients (10-fold and 25-fold higher than normal, respectively). It is proposed that enhanced RBC/EC adherence may contribute to the microcirculatory disorders observed in thalassaemia, especially in TI patients who are particularly known to suffer from leg ulcers.Keywords: b-thalassaemia major, b-thalassaemia intermedia, red blood cells, adhesion, endothelial cells.Blood¯ow is strongly in¯uenced by red blood cells (RBC)¯ow properties, namely RBC aggregability (their capacity to aggregate), deformability (ability to change shape) and adherence to endothelial cells (EC). These properties play a major role in haemodynamics, particularly in small blood vessels (the microcirculation), and their impairment has been linked to microcirculatory disorders in numerous pathological states.Thalassaemia (thal) is a congenital haemoglobinopathy, arising from imbalanced synthesis of either the alpha (a-thal) or the beta (b-thal) globin chain, which affects 1±2 million children annually throughout the world (Weatherall et al, 1995). Thalassaemia is characterized by morphological and functional erythrocyte anomalies, leading to chronic anaemia, severe iron overload in vital organs, and death in childhood or at adolescence. In addition, thalassaemic patients suffer from diverse clinical manifestations attributed to circulatory disorders, expressed by transient ischaemic attacks, microvessel obstruction leading to cerebral thrombosis and stroke, and chronic leg ulcers. b-thal patients are classi®ed as thal major (TM) or thal intermedia (TI) patients, mainly by the requirement for periodical blood transfusion in TM, which is not usually required for TI patients.The structural and functional abnormalities of thal RBC are associated with reduced deformability (Mohandas & Chasis, 1993) and increased aggregability (Chen et al, 1996). These are assumed to contribute to the microcirculatory disorders observed in thalassaemia.In recent years adhesion of RBC to EC has been considered to play an important role in the induction of vascular occlusion, as demonstrated in animal models of sickle cell disease and diabetes (Wautier et al, 1981;Kaul et al, 1993). In the present study we examined the adhesiveness of TM and TI RBC to EC, to further explore the possible role of RBC¯ow properties in thalassaemic microcirculatory disorders. METHODSBlood samples (2 ml) were received from volunteer TI and TM, splenectomized, patients. RBC were isolated by routine centrifugation, washed, and resuspended in culture medium (DMEM). The RBC were then placed on con¯uent cultured bovine aortic EC, in amounts suf®cient to cover the EC layer, and incubated for 45 min at 3...

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