Expression of integrin-αE by mucosal mast cells in the intestinal epithelium and its absence in nematode-infected mice lacking the transforming growth-factor-β1-activating integrin αvβ6

Peak intestinal mucosal mast cell (MMC) recruitment coincides with expulsion of Trichinella spiralis, at a time when the majority of the MMCs are located within the epithelium in BALB/c mice. Although expression of integrin-alpha(E)beta(7) by MMCs has not been formally demonstrated, it has been proposed as a potential mechanism to account for the predominantly intraepithelial location of MMCs during nematode infection. Co-expression of integrin-alpha(E)beta(7) and the MMC chymase mouse mast cell protease-1, by mouse bone marrow-derived mast cells, is strictly regulated by transforming growth factor (TGF)-beta(1). However, TGF-beta(1) is secreted as part of a latent complex in vivo and subsequent extracellular modification is required to render it biologically active. We now show, for the first time, that intraepithelial MMCs express integrin-alpha(E)beta(7) in Trichinella-infected BALB/c and S129 mice. In S129 mice that lack the gene for the integrin-beta(6) subunit and, as consequence, do not express the epithelial integrin-alpha(v)beta(6), integrin-alpha(E) expression is virtually abolished and recruitment of MMCs into the intestinal epithelium is dramatically reduced despite significant overall augmentation of the MMC population. Because a major function of integrin-alpha(v)beta(6) is to activate latent TGF-beta(1), these findings strongly support a role for TGF-beta(1), in both the recruitment and differentiation of murine MMCs during nematode infection.