Engagement of integrins by natural ligands or specific antibodies initiates biochemical signaling events within the cell, important for regulating different cell functions, such as migration, adhesion, proliferation, differentiation, apoptosis, and specific gene expression (1–3). Integrin-mediated cell adhesion has been shown to be accompanied by tyrosine phosphorylation of several proteins in a variety of cell types including lymphoid cells (4–7).