A model for cell adhesion mediated by dimeric binding was developed in a companion paper. To test the model, we used a micropipette adhesion frequency assay to measure dimeric E-selectin-Ig or monomeric soluble E-selectin (sE-selectin) interacting with dimeric P-selectin glycoprotein ligand 1 (PSGL-1) or monomeric soluble PSGL-1 (sPSGL-1). Higher adhesions were mediated by E-selectin-Ig interacting with PSGL-1 than sPSGL-1, whereas similar adhesions were mediated by sE-selectin interacting with PSGL-1 or sPSGL-1. Respectively fitting the measured kinetics of E-selectin-Ig adhesion to PSGL-1 by the newly developed dimeric model and to sPSGL-1 by a previous monomeric model resulted in a chi square much smaller than that resulted from respectively fitting the PSGL-1 data by the monomeric model and the sPSGL-1 data by the dimeric model. For sE-selectin, the goodness-offit was indifferent to whether the models matched or mismatched the ligand valencies. These results support the validity of the models and illustrate a strategy of using a dimeric ligand probe to discriminate multimeric from monomeric receptors. To apply the models and the strategy, we analyzed T cell receptor (TCR) interacting with dimeric peptide-major histocompatibility complex (pMHC). Adhesions of activated T cells were higher than those of naïve T cells. Respectively fitting the activated T cell data by the dimeric model and the naïve T cell data by the monomeric model resulted in chi squares much smaller than those resulted from respectively fitting the activated T cell data by the monomeric model and the naïve T cell data by the dimeric model. These results suggest that T cell activation converts TCR-pMHC interactions from monomeric to multimeric.
T cell activation enables T cell receptor to form multimeric bonds with peptide-major histocompatibility complex molecule