DiscussionThe ability to identify allosteric inhibitors of protein function is highly desirable in drug discovery. Here we describe the identification of steric and allosteric binding sites on the human Fcg Receptor IIIa (FcgRIIIa – CD16) using a novel affinity scaffold protein (Affimers). There are two versions of the scaffold, one based on a mammalian Stefin A (Stadler et al. 2011) and a second based on plant Cystatin A (Tiede et al. 2014). The tertiary structure of both types are homologous and the interaction with the target is mediated via 2 or 3 loops, selected from a highly diverse library using phage display. FcgR-ligand interactions constitute a complex biological system whereby multiple layers of complexity facilitate the fine-tuning of immune responses to infections, whilst maintaining an ability to rapidly switch off these responses following clearance of the infectious/inflammatory stimulus; thus preventing excessive tissue damage.