At present, the receptor for human PSGs remains unknown. Because human PSGs share 80% identity at the amino acid level, it is worth exploring whether all 11 members of the family bind to the same receptor to perform these functions. We performed our studies with two recombinant PSG1 proteins, which differ in the nature of the tag at the Cterminus. Both proteins had the same activity in target cells with small variations in the concentration of protein required to observe the effects reported.