Pleiotrophin is a heparin-binding growth factor that has mitogenic effects on fibroblast, epithelial, and endothelial cells. Pleiotrophin is made by many tissues, but is predominantly secreted by nervous tissue during development. Pleiotrophin induces neurite outgrowth and is involved in tumor growth and metastasis. Pleiotrophin binds with low affinity to the cell surface receptor nucleolin to inhibit HIV-1 infection and can also bind the receptor protein tyrosine phosphatase type Z (PTPRZ), syndecan-3, and anaplastic lymphoma kinase (ALK) receptors.