Affinity and kinetic analysis of Fcγ receptor IIIa (CD16a) binding to IgG ligands

Binding of pathogen-bound immunoglobulin IS (IgG) to cell surface Fc gamma receptors (FcyRs) triggers a wide variety of effector functions. The binding kinetics and affinities of IgG-Fc gamma R interactions are hence important parameters for understanding Fc gamma R-mediated immune functions. We have measured the kinetic rates and equilibrium dissociation constants of IgG binding to a soluble Fc gamma RIIIa fused with Ig Fc (sCD16a) using the surface plasmon resonance technique. sCE116a interacted with monomeric human IgG and its subtypes IgG1 and IgG3 as well as rabbit IgG with on-rates of 6.5 X 10(3) 8.2 X 10(3), 1.1 X 10(4) and 1.8 X 10(4)M(-1) s(-1), off-rates of 4.7 X 10(-3), 5.7 X 10(-3) 5.9 X 10(-3), and 1.9 X 10(-2) s(-1), and equilibrium dissociation constants of 0.72, 0.71, 0.56, and 1.1 mu m, respectively. The kinetics and affinities measured by surface plasmon resonance agreed with those obtained from real time flow cytometry and competition inhibition binding experiments using cell surface CD16a. These data add to our understanding of IgG-Fc gamma R interactions.