The microbiota as a component of the celiac disease and non-celiac gluten sensitivity

The mic obio a as a componen o he celiac disease and non-celiac glu en sensi i i y Lo a Nylund a , * , Ka i Kaukinen b , c , Ka i Lind o s a a Tampe e Cen e o Child Heal h Resea ch, Uni e si y o Tampe e and Tampe e Uni e si y Hospi al, Tampe e, Finland b Depa men o In e nal Medicine, Tampe e Uni e si y Hospi al, Tampe e, Finland c School o Medicine, Uni e si y o Tampe e, Finland a icle in o A icle his o y: Recei ed 20 No embe 2015 Accep ed 2 Janua y 2016 A ailable online 14 Janua y 2016 Keywo ds: Celiac disease Non-celiac glu en sensi i i y In es inal mic obio a Hos -mic obe in e ac ions Glu en- ee die summa y Die a y glu en p esen in whea , ye and ba ley induces se e al gas oin es inal diso de s, including celiac disease and non-celiac glu en sensi i i y (NCGS). Celiac disease is an immune-based en e - opa hy igge ed by inges ion o glu en in gene ically suscep ible indi iduals esul ing om he in e ac ion be ween gene ic and en i onmen al ac o s. Al hough glu en has been ecognized as he main en i onmen al igge o he disease, a specific ole o he in- es inal mic obio a in celiac disease de elopmen has been sugges ed. NCGS indi iduals de elop ad e se eac ions a e he exposu e o glu en. Due o he simila i ies in clinical ou comes and he absence o diagnos ic bioma ke s, i is challenging o di e en ia e NCGS om celiac disease. The ae iology o NCGS emains unknown, al hough he in ol emen o inna e immune mechanisms has been sugges ed. Since he influence o in es inal mic obio a on immune cell ho- meos asis and on educa ion o bo h inna e and adap i e immune sys em is well known, he ole o hos -mic obe in e ac ions in he non-celiac glu en sensi i i y ha e been hypo hesized. This e iew aims o summa ize he cu en knowledge o he con ibu ion o mic obio a o he pa hogenesis and/o onse o celiac disease. In addi ion, a b ie o e iew o he possible ole o he mic obio a componen s on he NCGS is p esen ed. ©2016 The Au ho s. Published by Else ie L d on behal o Eu opean Socie y o Clinical Nu i ion and Me abolism. This is an open access a icle unde he CC BY-NC-ND license (h p:// c ea i ecommons.o g/licenses/by-nc-nd/4.0/). *Co esponding au ho . E-mail add ess: lo a.nylund@u a.fi(L. Nylund). Con en s lis s a ailable a ScienceDi ec Clinical Nu i ion Expe imen al jou nal homepage: h p:// www.clinicalnu i ionexpe imen al.com h p://dx.doi.o g/10.1016/j.yclnex.2016.01.002 2352-9393/©2016 The Au ho s. Published by Else ie L d onbehal o Eu opeanSocie y o Clinical Nu i ion and Me abolism. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). Clinical Nu i ion Expe imen al 6 (2016) 17e24 1. In oduc ion Glu en- ela ed diso de s a e he umb ella e m o all condi ions ela ed o glu en inges ion, such as celiac disease and non-celiac glu en sensi i i y (NCGS). The p e alence o hese diseases has inc eased o e he pas 50 yea s, being an eme ging heal h p oblem wo ldwide. Cu en ly, celiac disease is conside ed he mos common ood in ole ance, p e alence being app oxima ely 1e2% o he popu- la ion [1]. In con as , he p e alence o NCGS has been es ima ed o be as high as 6% o he gene al popula ion, depending on he popula ion s udied [2]. The biological basis o glu en induced symp oms in he absence o celiac disease is unknown bu i has been sugges ed o be ela ed o immune e- sponses o componen s o whea apa om glu en, such as whea amylase- ypsin inhibi o s (ATIs) and e men able oligo-, di-, monosaccha ides and polyols (FODMAPs) [2,3]. The main gene ic componen o celiac disease, HLA-DQ2/DQ8 he e odime s, is well-known. Al hough hese HLA-DQ genes unde lie he diso de , only a small pe cen age o ca ie s de elop he disease and hus, o he gene ic and en i onmen al ac o s mus be in ol ed in he onse o celiac disease. This e iew aims o summa ize he cu en knowledge o he con ibu ion o mic obio a o pa hogenesis and/o onse o CD. In addi ion, a b ie o e iew o he possible ole o he mic obio a componen s on he de elopmen and/o onse o NCGS will be p o ided. 2. Celiac disease Celiac disease is an immune-based en e opa hy igge ed by inges ion o whea , ye and ba ley de i ed glu en in gene ically suscep ible indi iduals. Upon exposu e o glu en, inflamma o y cascade is induced in he small in es inal mucosa leading o illous a ophy, c yp hype plasia and inc eased numbe s o lymphocy es in he lamina p op ia. Dis up ion o in es inal illus s uc u e leads o impai ed epi helial ba ie unc ion esul ing in nu ien malabso p ion ha may cause se e e symp oms such as anaemia, os eopo osis and, in case o child en, o g ow h e a da ion. The clinical pic u e o he celiac disease is highly a iable and indi idual-specific. Classical symp oms o celiac disease include di e en gas oin es inal symp oms such as abdominal pain and dia hoea. Howe e , many CD pa ien s a e p edominan ly symp oma ic, showing bo h gas oin es inal and ex a-in es inal mani es a ions. In asymp oma ic pa ien s he diagnosis is o en delayed and hus he small-bowel mucosal damage may be se e e be o e he celiac disease is suspec ed. The e o e, ea ly diagnosis o he disease is c ucial o he p e en ion o pe sis en illous a ophy p edisposing o se e e compli- ca ions. Celiac disease is a li e-long disease ha canno be cu ed bu he symp oms can disappea and small bowel mucosal damage, in es inal inflamma ion and epi helial in eg i y a e imp o ed by commi men o a li e-long glu en- ee die . The main gene ic p edisposi ion o celiac disease a e he human leucocy e an igen (HLA) DQ2 and DQ8 haplo ypes. These HLA-DQ genes accoun o app oxima ely 40% o he gene ic isk o celiac disease [4]. Howe e , al hough hese genes unde lie he diso de , only a small pe cen age o ca ie s de elop disease. In addi ion, he disease conco dance in monozygo ic wins has been epo ed o be only 85% [5]. Thus, o he gene ic and en i onmen al ac o s mus be in ol ed in he onse o he diso de (Fig.1). Recen genome wide associa ion s udies ha e epo ed addi ional 39 non-HLA egions associa ed wi h suscep ibili y o celiac disease de elopmen [4]. In e es ingly, mos o hese egions con ain genes wi h immune ela ed unc ions, se e al o which a e also in ol ed in shaping he in- es inal mic obio a. In addi ion, al e ed exp ession o non-specific celiac disease isk-genes a ec ing he hos -mic obe in e ac ions has ecen ly been epo ed. Fo ins ance, a dec eased TOLLIP mRNA le els we e obse ed in un ea ed celiac pa ien s when compa ed o heal hy con ols [6]. TOLLIP is an in acellula p o ein ha inhibi s oll-like ecep o signalling and ailu e o up egula e i s ansc ip ion has been sugges ed o con ibu e o he ch onic inflamma ion in celiac and inflamma o y bowel dis- ease pa ien s [6,7]. These esul s sugges he po en ial ole o dis u bed hos -mic obe in e ac ion in he pa hogenesis o celiac disease. I is assumed ha abe an mic obio a di e si y and ela i e abundances o specific bac e ial axa lead o unc ional imbalance whe e he mu ualis ic ela ionship be ween he hos and his mic obes is dis u bed. De ia ions in he mic obio a communi y s uc u e has been associa ed wi h se e al local and sys emic diseases, possibly con ibu ing o he pa hogenesis and/o clinical mani es a ion o hese L. Nylund e al. / Clinical Nu i ion Expe imen al 6 (2016) 17e2418 diseases [8]. A specific ole o he in es inal mic obio a in celiac disease de elopmen has been sug- ges ed, bu he esul s emain con adic o y [6,9]. This inconsis ency may possibly be explained by di e en echniques used, di e en sample ypes analysed ( aecal ma e ial s biopsies), pa ien 's age ange (in an s, child en o adul s), small sample size and limi ed amoun o s udies pe o med. 2.1. Mic obio a in ea ly li e and isk o celiac disease The ini ial coloniza ion p ocess o he in an gas oin es inal ac o ms he basis o he subsequen mic obio a and immune esponse de elopmen , hus ha ing a majo influence on he la e li e heal h and p edisposi ion o he de elopmen o se e al immune-media ed diseases. Li e e en s occu ing in ea ly li e and causing dis u bances o he de eloping esiden mic obio a can lead o long-las ing dysbiosis wi h inc eased amoun s o ela i e abundances o one o mo e disease associa ed bac e ial species. In e es ingly, a high equency o in ec ious episodes as well as an ibio ic ea men s, known o a ec he in es inal mic obio a, ha e been associa ed wi h he onse o celiac disease in gene ically suscep ible in an s [10,11]. I has been sugges ed ha despi e he di e en li e e en s, also a specific disease-biased hos ge- no ype may selec o he fi s gu colonize s and hus con ibu e o he disease isk (Fig. 1). Se e al s udies ha e epo ed he influence o geno ype o in an s a amily isk o de eloping celiac disease (HLA-DQ2 s non-HLA-DQ2/8 geno ype) on he ea ly li e aecal mic obio a composi ion [12e14].Ina ecen s udy, 1 mon h old in an s wi h a high gene ic isk o celiac disease we e obse ed o ha e lowe p opo ion o Ac inobac e ia and highe p opo ion o Fi micu es and P o eobac e ia han in an s wi h low gene ic isk o disease de elopmen [14]. Mo eo e , HLA-DQ geno ype seems o specifically influence he coloniza ion p ocess o Bac e oides species [12]. In pa icula , an inc eased Bac e oides ulga us p e alence was associa ed wi h he geno ype o in an s a high isk o celiac disease de el- opmen , whe eas inc eased Bac e oides uni o mis p e alence was associa ed wi h a low gene ic isk [12]. Indeed, he mos cons an finding is he highe abundance o Bac e oides spp. in celiac disease pa ien s [9,15], al hough a ecen p ospec i e s udy epo ed a comple e lack o he membe s o phylum Bac e oide es in celiac disease p edisposed in an s [16]. In addi ion, Bac e oides agilis has been associa ed wi h an inc eased isk o celiac disease de elopmen in gene ically p edisposed Fig. 1. Fac o s con ibu ing o he onse o celiac disease. Bo h gene ic and en i onmen al ac o s con ibu e o he de elopmen o celiac disease. O hese, HLA-DQ2 and DQ8 as well as die a y glu en play a di ec ole in he dis u bed immune homeos asis and he subsequen Th1- ype immune esponse equi ed o he disease onse . The o he ac o s ei he di ec ly o indi ec ly lead o he in es inal mic obio a dysbiosis, which may also p omo e he de elopmen o celiac disease. HLA, human leucocy e an igen; PRRs, pa e n ecogni ion ecep o s. L. Nylund e al. / Clinical Nu i ion Expe imen al 6 (2016) 17e24 19 in an s who we e o mula- ed [13]. In e es ingly, polysaccha ide A p oduced by B. agilis has been shown o di ec he immune sys em ia i s abili y o di ec he de elopmen o CD4þT cells, hus inducing he di e en ia ion o Th1-lineage [17]. The e o e, i seems likely ha inc eased abundance o Bac e oides spp. con ibu es o he Th1 esponse ound in he small in es inal mucosa o celiac disease pa ien s [6,18]. Fu he mo e, a s udy by Sanz e al. [19] epo ed a educ ion in immunoglobulin A (IgA) -coa ed Bac e oides spp. in aeces o un ea ed and ea ed celiac pa ien s when compa ed o heal hy con ols, sugges ing ha hos de ences agains his bac e ial g oups may be educed in celiac disease, hus allowing i s inc eased coloniza ion. Immunoglobulin A is he p edominan an ibody p oduced by a mucosal su aces. Sec e o y IgA (sIgA) has di e se biological p ope ies such as immune exclusion, immunomodula ion and main enance o he in eg i y o mucosal ba ie s. In addi ion, i p o ides he fi s line o de ence agains in ading pa hogens by a ge ing mic obial an igens in he mucosal en i- onmen . Howe e , he main ole o sIgA seems o be he es ablishmen and main enance o ho- meos asis wi h he commensal mic obio a [20]. I has been sugges ed ha coa ing o commensal bac e ia by sIgA may ep esen a mechanism by which his disc imina ion be ween abundan no mal mic obio a and a e pa hogens a e made [20]. Dis up ed p oduc ion o sec e o y IgA has been conside ed a isk ac o o he de elopmen o gas oin es inal diso de s such as celiac disease [21]. IgA is also he mos abundan an ibody sec e ed in o he b eas -milk and he specifici ies o hese sIgAs a e shaped by ma e nal mic obio a ( e iewed in [22]). B eas milk sIgA p o ides he fi s sou ce o an ibody-media ed immune p o ec ion in he in es ine o b eas - ed neona e [23]. T ans e o hese ma e nal sIgA o he in an p omo es he es ablishmen o egula o y immune sys em and suppo s he mu ualis ic ela ionship wi h he commensal mic obio a [23]. In addi ion, he p esence o commensal mic obes is needed o he induc ion o he endogenous p oduc ion o IgA, which is slowly s a ed while he immune sys em de elops [24]. Thus, educ ion in in es inal sIgA seems o con ibu e o mic obio a dysbiosis and p o-inflamma o y esponse [24]. Mo eo e , he educ ion o o al G am-posi i e bac e ia popula ion, especially he abundance o Bifidobac e ium spp. [9,15] and he inc ease in he p opo ions o G am-nega i e bac e ia such as Clos idium g oups, P e o ella spp, and Esche ichia coli [15,18] ha e been epo ed in paedia ic celiac disease pa ien s wi h an ac i e disease. The educed abundance o bifidobac e ia may be o in e es , since hey ha e been sugges ed o alle ia e gas oin es inal symp oms o adul celiac pa ien s [25] as well as o educe abdominal pain in heal hy indi iduals [26]. Mic obio a dysbiosis o paedia ic celiac disease pa ien s ha e been sugges ed o be cha ac e ized by an inc eased mic obio a di e si y [27], al hough con adic o y finding has ecen ly been epo ed in a s udy u ilizing high- h oughpu mic oa ay me hod [18]. Fu he s udies u ilizing he high- h oughpu me hods a e needed o comp ehensi ely e alua e he mic obio a di e si y and species ichness associa ed wi h celiac disease. 2.2. Mic obio a in adul celiac disease pa ien s Al hough he majo i y o s udies e alua ing he mic obio a composi ion associa ed wi h celiac disease ha e been pe o med wi h paedia ic pa ien s, ew s udies ha e also assessed he mic obio a in adul CD pa ien s. Posi i e se o eac i i y agains di e en mic obial an igens in celiac disease pa ien s ha ing es ab- lished small-bowel mucosal damage wi h illous a ophy and c yp hype plasia ha e been epo ed [28,29]. These se ological esponses can be de ec ed al eady in he ea ly s ages o he diseases [28], sugges ing ha immune esponses o commensal mic obio a a e al eady p esen ea ly in he disease s age and hus may ha e a ole in he pa hogenesis o he celiac disease and he de elopmen o mucosal damage. The ole o in es inal mic obio a on di e en clinical mani es a ions o he disease was demon- s a ed in a s udy by Wacklin e al. [30], whe e he mic obio a composi ion, s uc u e and di e si y we e obse ed o di e depending on he mani es a ion o he disease, especially be ween in es inal symp oms (gas oin es inal symp oms o anaemia) and ex a-in es inal symp oms (de ma i is he - pe i o mis). The pa ien s wi h classical gas oin es inal symp oms had a highe amoun o P o eo- bac e ia han pa ien s wi h o he mani es a ion o he disease, whe eas pa ien s wi h anaemia had he lowes mic obial ichness and dis inc clus e ing o duodenal mic obio a p ofiles. L. Nylund e al. / Clinical Nu i ion Expe imen al 6 (2016) 17e2420 A e a glu en- ee die is ini ia ed, healing o he in es inal mucosa usually s a s. Mucosal healing is a g adual p ocess and i has been es ima ed ha he median ime needed o achie e a no mal illous heigh is 3.8 yea s [31]. Howe e , a significan ac ion o celiac disease pa ien s su e om pe sis en symp oms despi e an adhe ence o a glu en- ee die and no malized small bowel mucosa [32].In some pa ien s, symp oms can be explained by inad e en glu en in ake o he p esence o addi ional gas oin es inal disease [33]. In many cases he eason o pe sis en symp oms canno be explained [32]. Mic obio a dysbiosis obse ed in un ea ed celiac pa ien s is no comple ely es o ed a e adhe ence o a glu en- ee die , sugges ing ha some changes in mic obio a a e no seconda y o he inflamma o y milieu o he ac i e phase o he disease bu could play a p ima y ole in p edisposi ion o celiac disease de elopmen [15,34]. T ea ed celiac disease pa ien s wi h pe sis en symp oms ha e been epo ed o ha e a mic obio a dysbiosis, cha ac e ized by P o eobac e ia-domina ing duodenal mic obio a and educed mic obial ichness compa ed o ea ed pa ien s wi hou symp oms [35]. I has been sugges ed ha he IL17A p oducing cells play a majo ole in he pa hogenesis o celiac disease, ha bo h glu en and CD associa ed bac e ia p o oke an IL-17A esponse in he in es inal mucosa o CD pa ien s and ha he magni ude o he ad e se IL-17A eac ion o glu en is ma kedly influenced by he composi ion o he esiden mic obio a and he amoun o CD associa ed bac e ia p esen [36]. In hei s udy, Sj€ obe g e al. [36] used a mix u e o CD associa ed bac e ia (fi e P e o ella, one Lachnoanae obaculum and one Ac inomyces isola e) and glu en o challenge he biopsies aken om un ea ed and ea ed CD pa ien s and om clinical con ols. A diagnosis, pa ien s wi h CD we e obse ed o ha e highly ele a ed le els o IL-17A mRNA in hei jejunal mucosa. The le els e u ned o no mal le el on a glu en- ee die [36]. The celiac disease associa ed bac e ia analysed in ha s udy we e capable o inducing an IL-17A esponse on hei own, sugges ing ha his esponse seen in ac i e celiac disease could be (in pa ) di ec ed agains he CD -associa ed bac e ia. In addi ion, hese bac e ia de e mined he magni ude o he IL-17A esponse (ei he supp essing o enhancing) depending on whe he he pa ien had a s ong esponse o glu en diges alone o no . In e es ingly, all pa ien s ha showed a supp essed IL-17A esponse we e obse ed o be bo n du ing he Swedish celiac disease epidemic, whe eas child en bo n a e he epidemic showed con adic i e esponse. Homozygosi y o non- unc ional ucosyl ans e ase 2 (FUT2) gene leads o he absence o ABH blood g oups (FUT2 non-sec e o s a us) in body fluids. Recen ly, FUT2 non-sec e o s a us has been associa ed wi h he suscep ibili y o celiac disease in he Finnish popula ion [37]. Mo eo e , FUT2 sec e o s a us has been shown o be a majo de e minan o he gu mic obio a ichness and he composi ion o abundan mic obio a in heal hy indi iduals [38,39] as well as in C ohn's disease pa- ien s [40]. In e es ingly, eco e y a e he pa hogenic in ec ion was slowe in FUT2 deficien mice when compa ed o FUT2 su ficien con ols [41]. These esul s sugges ha ucosyla ion o in es inal epi helial cells may be a p o ec i e mechanism ha main ains he hos -mic obial in e ac ions, hus p e en ing he de elopmen o mic obio a dysbiosis. Fo comp ehensi e conclusions conside ing he ole o in es inal mic obio a in adul celiac disease pa ien s, u he s udies u ilizing high- h oughpu analysis a e needed. 2.3. E ec o glu en- ee die on mic obio a Cu en ly, he only e ec i e ea men a ailable o celiac disease is a li e-long adhe ence o a glu en- ee die . Al hough he die is e ec i e and sa e, i also c ea es social and economic bu dens o he pa ien s and some epo s ha e shown ha in es inal mic obio a is also a ec ed [15,42,43]. Mic obio a de ia ions obse ed in un ea ed celiac disease pa ien s we e only pa ly es o ed a e long- e m ea men wi h glu en- ee die . In young child en (6e12 yea s o age), who had ollowed glu en- ee die o wo yea s, a highe di e si y and a comple e ea angemen in Eubac e ium species communi y as well as changed me abolomics p ofiles we e obse ed [43]. In con as , he abundances o E. coli and S aphylococcus we e obse ed o no malize a e die a y ea men [15]. Ano he s udy epo ed sligh ly di e en mic obio a shi s, including dec eased abundance o bifidobac e ia, lac o- bacilli, Clos idium li usebu ense and Faecalibac e ium p ausni zii, whe eas p opo ions o E. coli and En e obac e iaceae inc eased [42]. Majo i y o hese mic obio a changes a e mos likely caused by a die a y e ec , since ansi ion o a glu en- ee die is associa ed wi h a educed in ake o complex polysaccha ides. Al hough a long- e m change in die a y habi s is equi ed o p o oke majo shi s in L. Nylund e al. / Clinical Nu i ion Expe imen al 6 (2016) 17e24 21 in es inal mic obio a composi ion, changes in daily ca bohyd a e in ake may a ec specific g oups o bac e ia o e a sho pe iod o ime. Fo example, consump ion o inulin o esis an s a ch inc eases he le els o Bifidobac e ium spp. and Faecalibac e ium p ausni zii o Ruminococcus b omii and Eubac- e ium ec ale, espec i ely [8]. These non-diges ible ca bohyd a es a e e men ed in he colon by i s mic obio a o yield ene gy o mic obial g ow h and end p oduc s such as sho -chain a y acids (SCFAs), mainly ace a e, p opiona e and bu y a e. SCFAs ha e a p o ound impac on gu heal h as an ene gy sou ce, an inflamma ion modula o , a asodila o and pa o gu mo ili y and wound healing. In addi ion, hey a e ene gy subs a es o he colonic epi helium (bu y a e) and pe iphe al issues (ac- e a e and p opiona e). The pa e ns o in es inal e men a ion and consequen ly he ypes and amoun s o SCFAs p oduced a e de e mined by how much ca bohyd a e is consumed and he composi ion o in es inal mic obio a [44]. Fu he s udies a e needed o shed ligh in o he ole o hese hos - mic obiome in e ac ions in he pa hogenesis o celiac disease and o he immune-media ed diseases. 3. Non-celiac glu en sensi i i y The p e alence o NCGS pa ien s is an eme ging heal h p oblem and i has been es ima ed o ac- coun o e 6% o he gene al popula ion, depending on he popula ion s udied [2]. Howe e , he eal p e alence o NCGS emains obscu e. Cu en ly he isk ac o s o NCGS ha e no been es ablished, al hough he diso de has a endency o be associa ed wi h emale gende and young o middle age [45]. Non-celiac glu en esensi i e indi iduals de elop ad e se eac ions such as gas oin es inal and ex a-in es inal symp oms a e exposu e o glu en [46]. Typical gas oin es inal symp oms include abdominal pain, bloa ing and al e ed bowel habi , he mos o en epo ed ex a-in es inal symp oms being a igue, headache, join o bone pain, mood diso de s and skin mani es a ions [2,45]. Due o he simila i ies in clinical ou comes and he absence o diagnos ic bioma ke s, i is challenging o di e - en ia e NCGS om o he glu en ela ed diso de s. Typically he diagnosis o NCGS is made a e he exclusion o celiac disease and whea alle gy by means o nega i e celiac se ology, nega i e his ological findings and nega i e es ing o specific immunoglobulin E (IgE). The diagnosis is u he confi med by a posi i e o al glu en challenge a e exclusion o glu en om he die o ew weeks. The glu en challenge should be implemen ed in a blinded ashion in o de o a oid a possible placebo e ec commonly seen in he die a y in e en ions [2]. Howe e , his app oach lacks specifici y and is di ficul o ca y ou in clinical p ac ise. In addi ion, he exclusion o i i able bowel synd ome (IBS) should be conside ed du ing he diagnos ic p ocess, since glu en may exace ba e he symp oms in hese pa ien s [47]. In con as , g ain- ee die o die low in FODMAPs ha e been shown o alle ia e he symp oms in some IBS pa ien s [48]. Al hough he ae iology o NCGS is unknown, i has been hypo hesized ha NCGS in ol es inna e immune mechanisms wi hou any implica ion o adap i e immune esponse [49]. This is in con as o celiac disease whe e o e exp ession o adap i e immuni y ma ke s is de ec ed. P e iously i has been shown ha NCGS pa ien s ha e no mal in es inal pe meabili y, no mal exp ession o igh junc ion p o eins claudin-1 and ZO-1 and significan ly highe exp ession o claudin-4 when compa ed o celiac disease pa ien s [46]. The up egula ion o claudin-4 coincided wi h he inc eased exp ession o oll-like ecep o (TLR) p o eins TLR1, TLR2 and TLR4 and dec eased amoun o egula o y T cells when compa ed o celiac disease pa ien s [46]. Toll-like ecep o s a e molecula pa e n ecogni ion e- cep o s o en esiding in he epi helial cell su ace ha ecognize mic obe-associa ed molecula pa - e ns (MAMPs). The dynamic hos -mic obe in e ac ion media ed by hese ecep o s is c ucial o he main enance o in es inal homeos asis. Mo eo e , in es inal mic obes ha e been shown o dec ease he in es inal pe meabili y by up egula ing he exp ession o igh junc ion p o eins [50]. Since in es inal mic obio a has an essen ial ole in egula ing he an igen milieu o en e ocy es, i may con ibu e o he pa hogenesis o onse o non-celiac glu en sensi i i y. Howe e , i s ole in he NCGS has no ye been s udied. 4. Conclusion Se e al s udies ha e demons a ed an al e ed in es inal mic obio a composi ion in celiac disease pa ien s. Howe e , he e is s ill no consensus ye ega ding he special mic obial species a ec ing L. Nylund e al. / Clinical Nu i ion Expe imen al 6 (2016) 17e2422 posi i ely o nega i ely o he disease p ocess. In addi ion, human s udies end o be co ela i e and hus e idence suppo ing he causali y be ween specific bac e ia and he pa hogenesis o ce ain diseases a e di ficul o ob ain. Majo i y o he s udies epo ing associa ion o mic obio a wi h celiac disease ha e been ca ied ou wi h paedia ic pa ien s, whose mic obio a is s ill de eloping and p one o he composi ional fluc ua ion due o he influence o a a ie y o en i onmen al ac o s. Thus, s udies conside ing he ma u e, es ablished mic obio a o adul pa ien s a e wa an ed. Mo eo e , s udies including la ge sample sizes and u ilizing he newes s a e-o - he-a me hods a e needed o comp ehensi ely analyse he ole o he in es inal mic obio a and i s me aboli es in bo h celiac disease and NCGS. Conflic o in e es None. Acknowledgemen s The Academy o Finland Resea ch Council o Heal h (25012812321 and 250129238), he Compe i i e S a e Resea ch Financing o he Expe Responsibili y A eas o Tampe e Uni e si y Hos- pi al (G an s 9P060, 9R018, 9S020, 9R034), he Sig id Juselius Founda ion and he P€ ai ikki and Saka i Sohlbe g Founda ion a e acknowledged o he financial suppo . Re e ences [1] Lud igsson JF, Le fle DA, Bai JC, Biagi F, Fasano A, G een PH, e al. The Oslo defini ions o coeliac disease and ela ed e ms. Gu 2013;62(1):43e52. [2] Sapone A, Bai JC, Ciacci C, Dolinsek J, G een PH, Hadji assiliou M, e al. Spec um o glu en- ela ed diso de s: consensus on new nomencla u e and classifica ion. BMC Med 2012;10. 13e7015-10-13. [3] Biesiekie ski JR, Pe e s SL, Newnham ED, Rosella O, Mui JG, Gibson PR. No e ec s o glu en in pa ien s wi h sel - epo ed non-celiac glu en sensi i i y a e die a y educ ion o e men able, poo ly abso bed, sho -chain ca bohyd a es. Gas oen e ology 2013;145(2). 320e8.e1-3. 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