Animal-free Recombinant Human Pleiotrophin is expressed in Human 293 cells as a secreted unglycosylated monomer. PTN is a member of a family of heparin-binding proteins that share sequence, structural, and functional similarity. Other members of this family include midkine (MK), and chicken retinoic acid- induced heparin-binding protein (RI-HB), an avian homologue of MK. The expression of all these cytokines is restricted and highly regulated during development.