Human and murine recombinant c-kit ligands support the development of human mast cells from umbilical cord blood cells: Ultrastructural identification

The recently identified ligand for C-kit, a protooncogene encoded by the Wlocus in mice, is a member of the tyrosine kinase receptor family with growth factor activity for mouse mast cells. Mature human mast cells regularly develop from agranular precursors in cord blood in long-term cocultures of cord blood and murine fibroblasts. Since the c-kit ligand is a product of murine fibroblasts, wc examined the growth effect of recombinant human c-kit ligand (stem cell factor), of recombinant murine c-kit ligand (mast cell growth factor), and of a partially purified fraction derived from mouse fibroblast culture supernatant on the mast cell lineage of humans by electron microscopy in 8-week cultures of cord blood cells. We found thai immature mast cells which developed in cultures containing the recombinant ligand for c-kit of human or murine origin as well as the naturally occurring c-kit ligand in.YI3 fibroblast supernatants were identical. Thus, each of these sources of the c-kil ligand exerted identical effects on the ontogeny of human mast cells as they develop from their agranular precursors in cord blood. Full maturity of factor-supported mast cells did not occur.