Role of LFA-1, CD2, VLA-5/CD29, and CD43 surface receptors in CD4+ T cell adhesion to B cells

We investigated the adhesion to B cells of CD4+ T cells both in the resting state and following activation by CD3 cross-linking or stimulation by PMA/ionomycine/IL2 for 6 days. Both resting and activated CD4+ T cell adhesion were inhibited by anti-LFA-1, -CD2, -VLA-5/CD29, and -CD43 antibodies, suggesting coordinated upregulation of T cell adhesion. The CD2 and LFA-1 adhesion pathways were found to act independently, as CD2 was functional in T cells not expressing LFA-1, and vice versa, and as specific antibodies had additive effects. In contrast, LFA-1- and VLA-5/CD29-specific antibodies did not have an additive blocking effect on CD4+ T cell adhesion, suggesting that efficient adhesion requires a competitive association of integrins with cytoskeleton elements. Although the involvement of fibronectin (coated to B cells via VLA-4) in VLA-5-mediated T cell adhesion to B cells is feasible, an anti-fibronectin and a VLA-4-specific antibody had no blocking effect. The involvement of an unidentified B cell ligand can also be envisaged.