text: We have described a protein from human placenta which supports growth of keratinocytes in culture (O'Keefe and Payne, 1985). This material has now been partially purified and partially characterized. It is precipitated by ammonium sulfate, destroyed by heat, acid, or trypsin, does not compete for binding with EGF, and migrates on gel filtration with a Mr of 41,000. The partially purified material also stimulates thymocyte growth but is not IL- 1, and it is uncertain whether the same factor stimulates both keratinocytes and thymocytes. In order to continue to purify and characterize this factor, we will test new purification methods and try to obtain enough purified material to produce antibody or to obtain a partial amino acid sequence which can be used to synthesize a polypeptide which can be used for immunization. The antibody will be used to further purify the material by western blotting. We will determine whether the more purified material continues to stimulate thymocytes or is separable from the IL-l-like activity. We will continue to validate a rapid 3H-thymidine assay that has facilitated our efforts at purification for use in assessing promotion of proliferation growth in cultured keratinocytes. We will characterize the biologic activities of the purified material by testing its ability to phosphorylate target cell membranes, to stimulate protein kinase C, to stimulate polyphosphoinositide metabolism, to alter intracellular calcium ion concentrations, and to interact with matrix components in enhancing keratinocyte growth. We will study interaction of the radioactively labelled factor with target cell including keratinocytes and other cell types and begin to study the receptor for the factor. Finally, we will use a radioimmunoassay for the factor to measure its concentration in plasma and tissues and to determine the cell of origin of the factor. These studies will elucidate the structure and function of this unique growth factor for keratinocytes.