Contributions of molecular binding events and cellular compliance to the modulation of leukocyte adhesion

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Physiology and Biophysics

First Committee Member

Vincent T. Moy - Committee Chair


The interaction of leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) is central to the regulation of adhesion in leukocytes. In this report, we investigated the mechanisms by which phorbol myristate acetate (PMA) promotes LFA-1-dependent cell adhesion. The adhesion of PMA-stimulated cells to immobilized ICAM-1 was quantified in direct force measurements acquired by atomic force microscopy (AFM). Enhanced adhesion of PMA-stimulated cells to immobilized ICAM-1 stemmed from an increase in the number of LFA-1/ICAM1 complexes formed between the two opposing surfaces on contact, rather than by affinity modulation of LFA-1. Single molecule force measurements revealed that the force spectrum of the LFA-1/ICAM-1 complex formed by PMA-stimulated cells is identical to the force spectrum of the complex formed by resting cells. Thus, PMA stimulation does not modify the mechanical strength of the individual LFA-1/ICAM-1 interaction. Instead, the enhanced cell adhesion of PMA-stimulated cells appeared to be a complex process that is correlated with changes in the mechanical properties of the cell. We estimated that changes in the elasticity of the cell gave rise to a greater than 10-fold increase in cell adhesion. We investigated this further by examining the contribution of LFA-1 receptor redistribution on the cell surface to cell adhesion. Using cell cross-linking that retarded receptor movement on the cell surface, we found a 20% reduction in the energy of de-adhesion. Finally, we examined alternative methods of cell stimulation that relied on increases in [Ca2+]i. The use of thapsigargin and ionomycin revealed similar increases in the energy of de-adhesion as stimulation of cells with PMA.


Biology, Cell; Biophysics, Medical

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