Regulation of Murine Mast Cell Homeostasis by TGF-β1 and CD4+CD25+C Regulatory T Cells

Understanding mast cell development is central to allergic disease pathophysiology. Our laboratory has previously shown that cytokines such as IL-4 and IL-10 inhibit mast cell development from bone marrow progenitors. These studies encouraged our interest in other regulatory cytokines, including transforming growth factor β1 (TGF- β1). TGF- β1 has many cellular sources, one of which is CD4+CD25 regulatory T cells (Tregs). We wanted to determine the effects of Transforming Growth Factor (TGF) βl on mast cell development. We find that TGFβl decreased FcεRI, c-Kit, T1/ST2 and FcεR expression, and inhibited granule formation in developing mast cells. Accessory cells were not required for this inhibition. Smad3-deficiency did not alter the response of bone marrow cells to TGFβ1. TGFβl inhibited expression of the FcεRI a subunit protein, without decreasing β or γ proteins. Mast cells derived in the presence of TGFβl were functionally impaired, as IgE-mediated cytokine secretion was greatly reduced. The changes in granule formation and surface antigen expression were long-standing, as they were not reversed by transfer to W/WV mice. The TGF-β1 dependent transcriptional regulation of bone marrow cells from which mast cells develop was examined through DNA microarray analysis. Wild type (WT) bone marrow cells were stimulated with IL-3+SCF+vehicle or IL-3+SCF+TGF-βI for 10 days and their transcriptomes* analyzed. The results identified which components of transcriptional regulation were regulated by TGF- β1. Of particular interest was the upregulation of the β subunit of the FcεRI, inspite of no receptor surface expression and the differential regulation of various mast cell proteases (MCPs). This initial survey provides a potential starting point for further analysis of the role of TGF-β1 -dependent signaling in developing mast cells. Because they produce TGF-β1 and/or IL-10, regulatory T cell-dependent murine mast cell inhibition was examined. Co-culture of mast cells with regulatory T cells for 6 days downregulated mast cell number, high affinity IgE receptor and c-Kit surface expression. This led to a decrease in TNFa release making mast cells functionally impaired. By using Tregs from IL-10 KO mice, this effect was proven to be IL-10 dependent. Mast cells are mediators of inflammatory disease. TGFβl and IL-10 may contribute to mast cell homeostasis by inhibiting maturation from bone marrow precursors. The effects of TGFβ1 and regulatory T cell derived IL-10 result in greatly diminished expression of cell surface markers, reduced granulation, and lack of responsiveness to IgE-mediated activation. Thus TGFβl and/or CD+CD25+ T cells can serve as potent and multifunctional regulators of mast cell maturation and/or function.* A set of genes that are expressed in a cell at any given time