ORIGINAL ARTICLE Diclofenac enhances allergic responses in a mouse peanut allergy model M. Bol-Schoenmakers 1 , R. Bleumink 1 , M. Marcondes Rezende 1,2 , E. Mouser 1 , I. Hassing 1 , I. Ludwig 1,3 , J. J. Smit 1,2 and R. H. H. Pieters 1 1 Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands, 2 Utrecht Center for Food Allergy, Utrecht, The Netherlands and 3 TIPharma, Leiden, The Netherlands Clinical & Experimental Allergy Correspondence: M. Bol-Schoenmakers, Utrecht University, IRAS, ITX, P.O. box 80177, NL 3508 TD Utrecht, The Netherlands. E-mail: m.bol-schoenmakers@uu.nl Cite this as: M. Bol-Schoenmakers, R. Bleumink, M. Marcondes Rezende, E. Mouser, I. Hassing, I. Ludwig, J. J. Smit and R. H. H. Pieters, Clinical & Experimental Allergy , 2011 (41) 424–433. Summary Background Diclofenac and other non-steroidal anti-inflammatory drugs (NSAIDs) interfere with cyclo-oxygenase-mediated synthesis of prostaglandins, resulting in the inhibition of inflammatory immune responses. In contrast, it is known that NSAIDs are able to induce gastrointestinal damage. Objective Our aim was to investigate whether NSAIDs are able to enhance sensitization or abrogate tolerance to food antigens. Methods Mice were exposed to diclofenac and sensitized to peanut using cholera toxin as a mucosal adjuvant. In a tolerance model, oral tolerance was induced via feeding of peanut 3 weeks before sensitization with peanut. Diclofenac was administered before peanut feeding. After 4 weeks, peanut-specific antibodies in the serum and cytokine production in the spleen were measured. Induction of intestinal damage after oral exposure with diclofenac and peanut 1 cholera toxin was examined microscopically. Results Diclofenac-exposed animals showed increased levels of peanut-specific IgG1, IgG2a and IgE in the serum compared with vehicle-treated animals. Furthermore, peanut-induced cytokine production in the spleen was elevated upon diclofenac treatment. Importantly, diclofenac did not induce peanut-allergic responses in the absence of the cholera toxin, although exposure to diclofenac and peanut 1 cholera toxin resulted in intestinal epithelial damage. Reduced peanut-specific antibody production in the case of oral tolerance was not reversed after diclofenac exposure. However, oral tolerance, as measured by inhibition of peanut-specific cytokine responses, was reverted by diclofenac. Conclusions These data point towards an increased risk for induction of food-allergic responses by diclofenac, when other circumstances are also in favour of induction of allergy. Keywords cyclo-oxygenase, diclofenac, mouse allergy model, non-steriodal anti- inflammatory drugs, oral tolerance, peanut allergy Submitted 22 October 2009; revised 11 June 2010; accepted 6 July 2010 Introduction Food allergy is reported in up to 8% of children below 3 years in the United States, and approximately 2% of the adults experience food-allergic reactions. However, the risk factors that are involved in the induction of food- allergic responses remain obscure [1]. The usual response to orally ingested antigens in the intestine is the induction of tolerance, but the presence of an adjuvant or distur- bance of the epithelial barrier function can result in adverse reactions [2, 3]. For instance, the use of non- steroidal anti-inflammatory drugs (NSAIDs) occasionally enhances wheat- or shrimp-induced anaphylaxis [4], and impairs oral tolerance induction to b-lactoglobulin [5] and ovalbumin [6]. A recent study shows that diclofenac is able to induce sensitization to a co-injected antigen (TNP- Ovalbumin) accompanied by antigen-specific antibody responses [7]. It is therefore of interest to investigate whether the administration of diclofenac is able to elicit or enhance the response towards food proteins. NSAIDs, like diclofenac, are originally designed to inhibit inflammation by inhibition of cyclo-oxygenase (COX) enzymes. COX enzymes (constitutive COX-1 and inducible COX-2) catalyse the conversion of membrane- derived arachidonic acid into biologically active mole- cules (prostanoids) like prostaglandins (e.g. PGE 2 , PGD 2 ) Experimental Models of Allergic Disease doi: 10.1111/j.1365-2222.2010.03594.x Clinical & Experimental Allergy, 41, 424–433  c 2010 Blackwell Publishing Ltd