The monoclonal antibody M.Ab.F11 recognizes junctional adhesion molecule-A (JAM-A) also known as the human platelet F11-Receptor (F11R) and JAM-1 is a cell adhesion molecule (CAM). JAM-A is a member of the immunoglobulin superfamily found on the surface of human platelets and at intercellular junctions of endothelial cells and epithelial cells. JAM-A belongs together with JAM-C (JAM-2) and JAM-B (VE-JAM or JAM-3) to a family of adhesion proteins with a V-C2 immunoglobulin domain organization. JAM plays an important role in tight junctions where it is involved in cell-to-cell adhesion through homophilic interaction. It codistributes with other tight junction components as ZO-1, 7H6 antigen, cingulin and occludin. JAM-A plays a role in platelet aggregation, secretion, adhesion, spreading.In the platelet F11R/JAM-A is a membrane protein involved in 2 distinct processes initiated on the platelet surface. Antibody-induced platelet aggregation and secretion both dependent on FcgammaRII and GPIIb/IIIa integrin, a process that may be involved in pathophysiological processes associated with certain thrombocytopenias. Antibody mediated platelet adhesion independent from FcgammaRII or fibrinogen receptor and that appears to play a role in physiological processes associated with platelet adhesion and aggregation. A physiological role for the F11R/JAM-A protein was demonstrated by its phosphorylation after the stimulation of platelets by thrombin and collagen. A pathophysiological role for the F11R/JAM-A was revealed by demonstrating the presence of F11R/JAM-A antibodies in patients with thrombocytopenia. Adhesion of platelets through the F11R resulted in events characteristic of the action of cell adhesion molecules (CAMs). Recent data suggests a role for F11R/JAM-A in the adhesion of platelets to cytokine-inflamed endothelial cells and thus in thrombosis and atherosclerosis induced in non-denuded blood vessels by inflammatory processes.