Analysis of ReceptorLigand Interactions by Surface Plasmon Resonance

Many immunological responses are often regulated by cell surface receptors in cell–cell recognition events. Such immune receptors on the cell surface typically exhibit low-affinity and fast-kinetic ligand interactions (e.g., K _d in the μM range, k _off  =  10⁻² to 20 s⁻¹ ). Real-time surface plasmon resonance (SPR) detection systems are generally useful for determining these binding parameters. However, several technical points should be considered because the determination of low-affinity binding and fast kinetics is often rather difficult. Here, we introduce a general procedure for SPR experiments and, moreover, show typical examples for ligand binding of immune cell surface receptors, including experimentally useful tips. We also show how to determine the thermodynamic characteristics using the nonlinear van’t Hoff and Arrhenius analyses. These affinity, kinetic, and thermodynamic parameters of immune–receptor binding are important for understanding immunological events as well as developing drugs and vaccines.