Alloimmunization in Hong Kong southern Chinese transfusion-dependent thalassemia patients.

factor-a, which increase endothelial expression of E-selectin. These molecules tether rolling neutrophils by binding to granulocyte Lewis x sialyated carbohydrate (CD15). This allows neutrophil integrins such as complement receptor 3 (CD11b) to adhere to the endothelium via interaction with its ligand intercellular adhesion molecule-1.7 The importance of CD64 (Fc-gamma receptor I) as a marker of endothelial adherence in patients with sickle cell disease and its notable increase during sickle cell crisis has been demonstrated. CD11b and CD64 expression on neutrophils is enhanced by G-CSF,8,9 providing further insight into mechanisms whereby G-CSF can enhance the trapping of neutrophils in the microcirculation, resulting in vascular occlusion, increased red cell transit time, and sickle cell polymer formation. In addition, sickle cells appear to be more adherent to neutrophils than to normal red cells.10 Sickle cells also increase neutrophil oxidative activity, which may be important in neutrophil-induced tissue damage during vaso-occlusive episodes. G-CSF, both by increasing the number of circulating neutrophils and enhancing neutrophil activation and endothelial attachment, may serve to transform a relatively stable steady state into a catastrophic cascade of events resulting in a sickle cell crisis and, in severe cases, multiorgan dysfunction. G-CSF should be given with extreme caution in patients with sickle cell disease. Further study is required to delineate the critical Hb S level that predisposes patients to developing G-CSF–induced sickle cell complications. Andrew Wei and Andrew Grigg