Objective: A role for leukocytes in vasoocclusion is becoming increasingly recognized. Here we investigate a possible role for the eosinophil in sickle cell anemia (SCA).
Patients and methods: Eosinophils were isolated from whole blood samples of 59 steady-state SCA homozygous SS and control individuals using Percoll gradient separation, followed by immunomagnetic sorting. Adhesion of cells to FN was evaluated using static adhesion assays (60 min, 37 degrees C, 5% CO2) and eosinophil adhesion molecular expression was observed by flow cytometry.
Results: SCA patients presented significantly elevated absolute eosinophil numbers. Furthermore, eosinophils isolated from these individuals demonstrated a significantly greater adhesion ( approximately 70% increased) to fibronectin (FN) than normal eosinophils in static adhesion assays. Coincubation of eosinophils with integrin-blocking monoclonal antibodies in adhesion assays showed that an association of the VLA-4, LFA-1, and Mac-1 integrins mediate the adhesion of SCA eosinophils to FN. Flow cytometry demonstrated that the expression of these integrins, however, was unaltered on the surface of SCA eosinophils, suggesting that the increased SCA eosinophil adhesion is a consequence of increased integrin affinity or avidity. SCA eosinophil adhesion to FN was further increased by the cytokine, GM-CSF, indicating that inflammation processes may further stimulate eosinophil adhesion in these patients.
Conclusion: We report that eosinophil numbers may be significantly increased in SCA individuals and that these cells appear to exist in an activated state. Such alterations may indicate a role for the eosinophil in the vasooclusive process.