ADHESIVE BOND DYNAMICS IN CONTACTS BETWEEN T-LYMPHOCYTES AND GLASS-SUPPORTED PLANAR BILAYERS RECONSTITUTED WITH THE IMMUNOGLOBULIN-RELATED ADHESION MOLECULE CD58

The interaction of the IT cell glycoprotein CD2 and its ligand CD58 is important for T cell interaction with antigen-presenting and target c ells, The binding interaction is of low affinity and has a fast off-ra te (>5 s(-1)) ill solution, However, solution measurements may not acc urately predict the behavior of molecules in an adhesive contact area, Interaction between T cells that express CD2 and glass-supported plan ar bilayers containing purified and fluorescently labeled CD58 leads t o accumulation of CD58 (fluorescence) in the cell/ bilayer contact are a, CD58 molecules accumulated within the contact area in excess of the CD58 density in the bilayer outside the contact area call be consider ed as bound by cell surface CD2. Here, this phenomena and fluorescence photobleaching recovery were utilized to determine whether CD2-CD58 b onds are transient in contact areas, Fluorescent CD58 molecules accumu lated in the T cell-bilayer inter face were completely bleached, The b leached CD58 molecules accumulated in the contact area were rapidly re placed by fluorescent CD58 that diffused into the contact area from ad jacent bilayer regions outside the contact area, Rapid recovery of the accumulated fluorescence directly demonstrates that the CD2-CD58 bond s are dissociating and that the dissociation leads to partner exchange , rather than rebinding of the same CD2-CD58 pairs, This suggests that the solution off-rate provides an accurate description of CDB-CD58 in teraction in contact areas, Accumulated fluorescent IgG in contacts be tween K562 cells expressing low affinity Fe receptors and planar bilay ers with fluorescent IgG bound to hapten-derivitized phospholipids dis played slower recovery than CD58 by a factor of 10, This suggests that the Fc receptor-IgG interaction has a longer life-time than the CD2-C D58 interaction, These findings have implications for the mechanism of signaling by CD2 and the mechanism of cell detachment from large numb ers of transient interactions.