Monoclonal antibodies (mAbs) directed against E2, a 32-kDa transmembrane protein 
encoded by the MIC2 gene located in the pseudoautosomal region, induce a 
transbilayer movement of phosphatidylserine and, to a lesser extent, 
phosphatidylethanolamine in human thymocytes and a Jurkat T lymphocytes. The 
translocation of phosphatidylserine has been evidenced by using either 
derivatization of anionic phospholipids with trinitrobenzenesulfonate (TNBS) or 
cytofluorimetry after labeling of cells with antiphosphatidylserine antibodies. 
The perturbation of membrane phospholipids induced by anti-E2 mAbs was further 
evidenced by labeling the cells with merocyanine 540. The specificity of 
anti-E2-induced perturbations of membrane asymmetry was tested by using a number 
of mAbs able to activate T cells, including CD3 and CD2. The results strongly 
suggest that anti-E2-induced changes in PtdSer are related to cell aggregation 
since the same mAbs specifically induce the aggregation of both thymocytes and 
Jurkat cells and since the E2 molecule has been previously implicated in the 
adhesive properties of human T cells with erythrocytes.