Although it has been shown that mast cell-deficient mice have diminished innate immune
responses against bacteria, the most important immunoprotective factors secreted from
activated mast cells have not been identified. Mouse mast cell protease 6 is a tetramer-
forming tryptase. This serine protease is abundant in the secretory granules and is
exocytosed upon bacterial challenge. Here we have described the generation of a mast cell
protease-6-null mouse. Our discovery that mice lacking this neutral protease cannot …