Introduction Innate immunity is attenuated in patients with Crohn's disease (CD) with impaired neutrophil recruitment to skin and bowel, delayed clearance of Escherichia coli from the skin, and impaired secretion of pro-inflammatory cytokines from macrophages (Marks et al, 2006; Smith et al, 2009). The primary defect of acute inflammation results in failure to eradicate bacterial flora entering the bowel wall leading to the chronic granulomatous inflammation characteristic of CD. Microarray analysis of peripheral blood monocyte derived macrophage mRNA expression, confirmed by qPCR, revealed that ADAMDEC1 (ADAM like Decysin1) was under-expressed in 10% (6/60) of CD patients. ADAMDEC1, a Metalloprotease and Decysin, is part of a family of proteins involved in wound healing and tissue repair, and is almost exclusively expressed in macrophages, dendritic cells and the gastrointestinal tract. To determine the role of this protein we examined E coli induced inflammation and Dextran Sodium Sulphate (DSS) colitis in the Adamdec1 knockout (KO) mouse.
Methods In an acute colitis model, Adamdec1 KO mice were exposed to 2% DSS for 7 days. Controls, wild type (WT) litter mates, were age, weight and sex matched (n=11 per group). Clinical colitis scores (weight loss, PR blood, loose stool) were recorded daily. Histology was obtained from small and large bowels. For bacterial inflammation, 5×108 heat killed E coli (HkEc) were injected subcutaneously (SC) into two sites on the backs of KO and WT mice (n=8 per group). Mice were weighed, injection sites inspected for ulceration and subcutaneous inflammatory nodules measured, daily. Injection sites were excised at different time points for histology and identification of infiltrating cells by FACS.
Results Adamdec1 KO mice were more susceptible to DSS colitis. They demonstrated higher clinical colitis scores with an earlier and more dramatic weight loss (p<0.001). A more florid inflammatory response was seen on histology. In response to a subcutaneous injection of E coli, Adamdec1 KO mice had significantly smaller inflammatory nodules and less ulceration at the injection sites after 48–72 h, compared with WT mice (p<0.001).
Conclusion Mice lacking Adamdec1 develop a phenotype that closely mirrors that observed in patients with CD, an attenuated and delayed E coli induced acute inflammatory and an increased susceptibility to bowel inflammation. These results suggest ADAMDEC1 plays an important role in the acute inflammatory response to bacteria and has a protective role within the intestine, reduced levels may have a pivotal role in the development and persistence of CD.
Competing interests None declared.
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