Genotype-dependent effects of TGF-ß1 on mast cell function: targeting the Stat5 pathway.

We previously demonstrated that TGF-ß1 suppresses IgE-mediated signaling in human and mouse mast cells in vitro, an effect that correlated with decreased expression of the high-affinity IgE receptor, FcεRI. The in vivo effects of TGF-ß1 and the means by which it suppresses mast cells have been less clear. This study shows that TGF-ß1 suppresses FcεRI and c-Kit expression in vivo. By examining changes in cytokine production concurrent with FcεRI expression, we found that TGF-ß1 suppresses TNF production independent of FcεRI levels. Rather, IgE-mediated signaling was altered. TGF-ß1 significantly reduced expression of Fyn and Stat5, proteins critical for cytokine induction. These changes may partly explain the effects of TGF-ß1, because Stat5B overexpression blocked TGF-mediated suppression of IgE-induced cytokine production. We also found that Stat5B is required for mast cell migration toward stem cell factor, and that TGF-ß1 reduced this migration. We found evidence that genetic background may alter TGF responses. TGF-ß1 greatly reduced mast cell numbers in Th1-prone C57BL/6, but not Th2-prone 129/Sv mice. Furthermore, TGF-ß1 did not suppress IgE-induced cytokine release and did increase c-Kit-mediated migration in 129/Sv mast cells. These data correlated with high basal Fyn and Stat5 expression in 129/Sv cells, which was not reduced by TGF-ß1 treatment. Finally, primary human mast cell populations also showed variable sensitivity to TGF-ß1-mediated changes in Stat5 and IgE-mediated IL-6 secretion. We propose that TGF-ß1 regulates mast cell homeostasis, and that this feedback suppression may be dependent on genetic context, predisposing some individuals to atopic disease.

ADAM10 is required for SCF-induced mast cell migration.

A Disintegrin and Metalloproteinase (ADAM)-10 plays critical roles in neuronal migration and distribution. Recently, ADAM10 deletion was shown to disrupt myelopoiesis. We found that inducible deletion of ADAM10 using Mx1-driven Cre recombinase for a period of three weeks resulted in mast cell hyperplasia in the skin, intestine and spleen. Mast cells express surface ADAM10 in vitro and in vivo, at high levels compared to other immune cells tested. ADAM10 is important for mast cell migration, since ADAM10-deficiency reduced c-Kit-mediated migration. As with some mast cell proteases, ADAM10 expression could be altered by the cytokine microenvironment, being inhibited by IL-10 or TGFß1, but not by several other T cell-derived cytokines. Collectively these data show that the ADAM10 protease is an important factor in mast cell migration and tissue distribution, and can be manipulated by environmental cues.

Myeloid-derived suppressor cells enhance IgE-mediated mast cell responses.

Mast cells and MDSCs are increased by parasitic infection and tumor growth. We previously demonstrated that enhanced MDSC development in ADAM10 transgenic mice yielded resistance to Nb infection and that coculturing MDSCs and mast cells enhanced cytokine production. In the current work, we show that MDSC-mast cell coculture selectively enhances IgE-mediated cytokine secretion among mast cells, without increasing MDSC cytokine production. This effect was independent of cell contact and elicited by Ly6C(+) and Ly6C/G+ MDSC subsets. These interactions were functionally important. MDSC depletion with the FDA-approved drug gemcitabine exacerbated Nb or Trichinella spiralis infection and reduced mast cell-dependent AHR and lung inflammation. Adoptive transfer of MDSC worsened AHR in WT but not mast cell-deficient Wsh/Wsh mice. These data support the hypothesis that MDSCs enhance mast cell inflammatory responses and demonstrate that this interaction can be altered by an existing chemotherapeutic.