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 intraepithelial 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)-β1-dependent in vitro. TGF-β1, which is secreted within tissues as a biologically inactive complex with latency-associated peptide, requires extracellular modification to become functionally active. The integrin-ανβ6 mediates local activation of TGF-β1 in association with epithelia. Using T. spiralis-infected β6−/− 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. spiralis-infected β6−/− mice compared with infected β6+/+ controls. Despite these changes, β6−/− mice still appeared to expel the worms normally. We postulate that compromised TGF-β1 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 β6−/− mice.