Transforming growth factor alpha （TGF-α）, a polypeptide of 5.5kDa that is partially homologous to epidermal growth factor （EGF）, is important in the control of glial and Schwann cell proliferation and survival of differentiated neurons. TGF-α is a mitogenic polypeptide that is able to bind to the EGF receptor/EGFR and to act synergistically with TGF-β to promote anchorage-independent cell proliferation in soft agar. Although TGF-α commonly acts via autocrine or paracrine signaling in solid tissues, it can also mediate paracrine signaling by activated macrophages, monocytes, neutrophils, and eosinophils.