Human dermal endothelial cells express membrane-associated mast cell growth factor.

Mast cell growth factor (MGF), a molecule that serves as a ligand for the receptor tyrosine kinase c-kit, is important in mast cell differentiation, migration, and activation. Previous studies of paraffin-embedded human skin using antibody to murine MGF and reverse transcription-polymerase chain reaction have demonstrated MGF protein and mRNA expression in keratinocytes and isolated dermal cells. We utilized a monoclonal antibody to human MGF to further define patterns of immunoreactivity in frozen specimens of neonatal and adult skin from normal individuals and from patients with urticaria pigmentosa. In addition to keratinocytes and isolated dermal cells in normal and urticaria pigmentosa skin, MGF was detected in cells lining superficial and mid-dermal vessels. Co-expression of MGF and the vascular antigen CD31, and immunoelectron microscopy, identified MGF-positive cells as endothelial cells. Patterns of endothelial MGF expression were not influenced by mast cell degranulation and endothelial E-selectin induction in vitro. By ultrastructure, unfixed specimens demonstrated MGF expression both within the endothelial cytoplasm and in association with lumenal, but not ablumenal, surfaces. Specimens fixed with Nakane's solution had diminished endothelial cytoplasmic MGF reactivity, but lumenal expression was maintained, suggesting persistence of a membrane-associated reactivity. MGF mRNA was also detected in cultured dermal microvascular endothelial cells using reverse transcription-polymerase chain reaction. These data establish human dermal endothelial cells as sites of MGF production and expression in human skin. Mast cell precursors must home to skin via vascular channels and differentiate in the immediate perivascular space. Thus, endothelial MGF may be an important determinant of adhesion and differentiation of mast cell progenitors expressing receptors for MGF.