Aberrant mucosal mast cell protease expression in the enteric epithelium of nematode-infected mice lacking the integrin αvβ6, a transforming growth factor-β1 activator

infection of mice with the nematode Trichinella spiralis triggers recruitment and differentiation of intra-epithelial intestinal mucosal mast cells expressing mouse mast cell protease 1 (Mcpt-1), which contributes to expulsion of the parasite. Expression of Mcpt-1 is transforming growth factor (TGF)-beta 1-dependent in vitro. TGF-beta 1, which is secreted within tissues as a biologically inactive complex with latency-associated peptide, requires extracellular modification to become functionally active. The integrin-alpha(v)beta(6) mediates local activation of TGF-beta 1 in association with epithelia. Using T. spiralis-infected beta(-/-)(6) mice, we show accumulation of mucosal mast cells in the lamina propria of the small intestine with minimal recruitment into the epithelial compartment. This was accompanied by a coordinate reduction in expression of both Mcpt-1 and -2 in the jejunum and increased tryptase expression, whereas Mcpt-9 became completely undetectable. in contrast, the cytokine stem cell factor, a regulator of mast cell differentiation and survival, was significantly up-regulated in T spiratis-infected beta 6(-/-) mice compared with infected beta(+/+)(6) controls. Despite these changes, beta(-/-)(6) mice still appeared to expel the worms normally. We postulate that compromised TGF-beta(1), activation within the gastrointestinal epithelial compartment is a major, but not the only, contributing factor to the observed changes in mucosal mast cell protease and epithelial cytokine expression in beta(-/-)(6) mice.