Introduction The pathogen recognition receptor, NLRP3, and its inflammasome are implicated in the innate immunity.1 Both intracellular and extracellular stressors induce its activation including the bacterial protein muramyl dipeptide,2 also recognised by NLRC2 (NOD2) which is known to be associated with Crohn's disease (CD). Little is known about expression of the NLRP3 inflammasome in normal gastrointestinal tract (GIT) or in CD, therefore the expression profile of four inflammasome proteins in the GIT has been investigated in this study.
Methods Paraffin embedded colonic tissue from healthy controls (HC) and CD patients were cut and fixed on slides. Protein antigens were exposed by pressure cooker heating in 0.01% antigen retrieval solution and water. Following application of a primary antibody (anti-NLRP3, anti-ASC, anti-pyrin, anti-caspase-1) the proteins were observed by washing in DAB/chromogen solution, following incubation with a Horseradish peroxidase-labelled secondary antibody. Degree of staining was assessed using a validated Quick score model3 where intensity of staining is scored 0–3, and proportion of cells stained is scored 0–5, a maximum Quick score per sample of 8. Differences in expression between HC and CD samples were analysed using Mann–Whitney U test.
Results Colonic biopsies from 20 HC and 20 CD patients were stained for NLRP3, ASC, Pyrin and Caspase-1 protein expression. All four proteins were expressed in HC and CD tissue. There were significant differences in expression of all 4 proteins when HC and colonic CD samples were compared (Abstract PTU-116 table 1).
Conclusion The NLRP3 inflammasome is expressed in normal, healthy GIT mucosa and is upregulated in colonic tissue from CD patients with active disease. This suggests the NLRP3 inflammasome may play a role in mucosal immunity in CD patients.
Competing interests None declared.
References 1. Petrilli V, Dostert C, Muruve DA, et al. The inflammasome: a danger complex triggering innate immunity. Curr Opin Immunol 2007;19:615–22.
2. Martinon F, Agostini L, Meylan E. Identification of bacterial muramyl dipeptide as activator of the NALP3/cryopyrin inflammasome. Curr Biol 2004;14:1929–34.
3. Detre S, Saclani Jotti G, Dowsett M. A “quickscore” method for immunohistochemical semiquantification: validation for oestrogen receptor in breast carcinomas. J Clin Path 1995;48:876–8.
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