GM-CSF downregulates expression of tryptase, Fc epsilon RI and histamine in HMC-1 mast cells.

Fibroblast-derived growth factors like SCF are able to upregulate the expression of mast cell characteristics in human multilineage hematopoietic progenitor cells. Other factors, like GM-CSF, have been reported to inhibit this process, probably by the competitive recruitment of cells not belonging to the mast cell lineage. In this study, we investigated the influence of GM-CSF on immature mast cells of the HMC-1 cell line which already show low-level expression of mast cell tryptase, histamine and Fc epsilonRI alpha. Culture of HMC-1 cells with mast-cell-conditioning medium, containing fibroblast supernatants, upregulated tryptase activity, histamine contents and expression of Fc epsilonRI alpha. However, addition of GM-CSF (10 ng/ml) markedly downregulated these mast cell markers, without affecting proliferation and viability of cells. Thus, GM-CSF may provide an inhibitory signal during mast cell differentiation and probably even downregulates mast cell characteristics in more differentiated cells.