Mouse Paneth cell antimicrobial function is independent of Nod2

<jats:sec> <jats:title>Objective</jats:title> <jats:p> Although polymorphisms of the <jats:italic>NOD2</jats:italic> gene predispose to the development of ileal Crohn's disease, the precise mechanisms of this increased susceptibility remain unclear. Previous work has shown that transcript expression of the Paneth cell (PC) antimicrobial peptides (AMPs) α-defensin 4 and α-defensin-related sequence 10 are selectively decreased in <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> mice. However, the specific mouse background used in this previous study is unclear. In light of recent evidence suggesting that mouse strain strongly influences PC antimicrobial activity, we sought to characterise PC AMP function in commercially available <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> mice on a C57BL/6 (B6) background. Specifically, we hypothesised that <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> B6 mice would display reduced AMP expression and activity. </jats:p> </jats:sec> <jats:sec> <jats:title>Design</jats:title> <jats:p> Wild-type (WT) and <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> B6 ileal AMP expression was assessed via real-time PCR, acid urea polyacrylamide gel electrophoresis and mass spectrometry. PCs were enumerated using flow cytometry. Functionally, α-defensin bactericidal activity was evaluated using a gel-overlay antimicrobial assay. Faecal microbial composition was determined using 454-sequencing of the bacterial 16S gene in cohoused WT and <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> littermates. </jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p> WT and <jats:italic> Nod2 <jats:sup>−/−</jats:sup> </jats:italic> B6 mice displayed similar PC AMP expression patterns, equivalent α-defensin profiles, and identical antimicrobial activity against commensal and pathogenic bacterial strains. Furthermore, minimal differences in gut microbial composition were detected between the two cohoused, littermate mouse groups. </jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Our data reveal that Nod2 does not directly regulate PC antimicrobial activity in B6 mice. Moreover, we demonstrate that previously reported Nod2-dependent influences on gut microbial composition may be overcome by environmental factors, such as cohousing with WT littermates.</jats:p> </jats:sec>