Background: Matrix metalloproteinase-7 (MMP7) processes mouse pro-␣-defensins to bactericidal forms in Paneth cells, and MMP7(Ϫ/Ϫ) mice are considered to be ␣-defensin-null. Results: Activated ␣-defensins occur in the colonic lumen of MMP7(Ϫ/Ϫ) mice. Conclusion: ␣-Defensins are activated in MMP7(Ϫ/Ϫ) large bowel lumen by alternative proteolytic conversion mechanisms. Significance: MMP7(Ϫ/Ϫ) mice are unsuitable for studying ␣-defensin deficiency in large intestine.

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In mice, Paneth cell α‐defensins, termed cryptdins (Crps), are converted intracellularly from inactive precursors to bactericidal forms by matrix metalloproteinase‐7 (MMP‐7). Because it is possible that other extracellular proteinases may be capable of similar processing, we tested whether secreted proCrps are converted to active forms in the MMP‐7−/− mouse. Protein extracts from complete (organ plus luminal contents) ileum, cecum, and colon of MMP‐7−/− and wild‐type C57Bl/6 mice were compared by gel permeation chromatography and acid‐urea (AU)‐PAGE. As anticipated, MMP‐7−/− ileum lacked appreciable levels of processed Crps. However, high levels of apparent Crps were purified from the cecum and colon of MMP‐7−/− mice. N‐terminal sequencing and mass spectrometry identified α‐defensins consisting of a mixture of native Crps, N‐terminally truncated Crps, and Crps with elongated N termini that retain proregion residues near the proregion‐Crp junction. Thus, secreted mouse proCrps may be processed in the large bowel lumen, even in the absence of the intracellular activating enzyme. Also, the MMP‐7−/− mouse may be a useful model of innate mucosal immunity in the small intestine, but the knockout is not α‐defensin deficient in cecum or distal colon, downstream from the site of precursor secretion in small intestinal crypts of Lieberkühn.Supported by NIH grants DK044632, AI059346, and AI057757.