CD4+ lymphocytes require platelets for adhesion to immobilized fibronectin in flow: role of beta(1) (CD29)-, beta(2) (CD18)-related integrins and non-integrin receptors

The role of platelets in T-lymphocytes adhesion is not clear yet. Herpesvirus saimiri (HVS)-infected CD4(+) T-lymphocytes were placed into polystyrene plates pre-coated with fibronectin. The adherent T-cells were enumerated by image analysis. Under static condition, 38+/-10cells/mm(2) adhered and addition of gel-filtered platelets (GFP) and PMA enhanced cell adhesion 4.3- and 4.1-fold. Using PMA plus GFP 11.9-fold enhancement in cell adhesion was achieved. In contrast, under flow (200s(-1)), neither basal adhesion nor following separate addition of PMA or GFP was observed, whereas combined addition of PMA and GFP induced noticeable adhesion (34cells/mm(2)). The adhesion was inhibited by blockade of alpha(5)-integrin (CD49e, 87%), beta(2)-integrin (CD18, 78%), CD40L (60%), PSGL-1 (CD162, 60%), and CD40L plus PSGL-1 (83%). Thus, activated platelets promote activated T-cell adhesion to fibronectin under flow via integrins (alpha(5)beta(1), and alpha(L)beta(2)), CD40-CD40L and P-selectin-PSGL-1 mediated interactions.