GIF binds GM-CSF and IL-2 via mutually exclusive epitopes
Previous studies demonstrated that GIF inhibits the biological activities of both ovine GM-CSF and ovine IL-2 in soft bone marrow cell colony and T-cell proliferation assays, respectively20. To characterize the interaction between GIF and its two target cytokines kinetically and in terms of binding affinity we employed bio-layer interferometry (BLI) using biotinylated GIF immobilized onto streptavidin-coated BLI sensors. Our measurements reveal that GIF binds GM-CSF and IL-2 with high affinities yet with quite distinct kinetic binding profiles (Fig. 5a,b). On one hand, binding of GM-CSF to GIF is characterized by rather slow association kinetics and very slow dissociation kinetics leading to a KD=27 nM, whereas IL-2 binds to GIF with ∼60-fold higher affinity (KD=0.47 nM) that can be recapitulated by fast association kinetics and moderately slow dissociation kinetics (Fig. 5a,b).