The adhesion of lymphocytes to one another or to other cells is a poorly understood phenomenon which is presently analyzed via purely qualitative and non-physical methods. To address this concern, the Principal Investigators propose to characterize fundamental physical, chemical, and molecular interactions that occur during the process of lyphocyte adhesion. This characterization will be achieved through: - Measurement of affinity constants of known adhesion molecules. - Quantification of the rate of change of the rate of change of the intercellular contact area during the adhesion event. Techniques in fluorescence energy transfer spectroscopy, video microscopy, and digital image analysis will be employed for this analysis and the results will be used to develop physical and mathematical models of lymphocyte adhesion processes.