Small-Bowel Mucosal Transglutaminase-2-specific Autoantibody Deposits in Coeliac Disease

Abstract

Keliakia on autoimmuunitauti, jota todetaan väestössä jopa 1-2 %:lla. Klassiset oireet ripuli, imeytymishäiriöt ja laihtuminen ovat tänä päivänä harvinaisempia kuin aiemmin ja usein oireet ovat lieviä tai puuttuvat kokonaan. Nykyisin keliakian diagnoosiin vaaditaan vehnän, ohran tai rukiin valkuaisaineen, gluteenin, aiheuttama ohutsuolen limakalvovaurio, joka korjaantuu gluteenittomalla ruokavaliolla. Aiemman tutkimustiedon mukaan nykyisten diagnostisten kriteerien perusteella ei kaikkia keliakiapotilaita tunnisteta. Apuna keliakian diagnostiikassa käytetään seerumin transglutaminaasi-2 autovasta-aineiden tunnistamiseen perustuvia testejä. Nämä vasta-aineet muodostetaan ohutsuolen limakalvolla, josta ne ovat alustavien tutkimusten mukaan todettavissa keliakiapotilailla vaikka seerumissa ei vasta-aineita olisikaan mitattavissa.

Tämän väitöskirjatutkimuksen tavoitteena oli selvittää, voisiko ohutsuolen limakalvon transglutaminaasi-2-spesifisten autovasta-ainekertymien määrittäminen parantaa keliakian diagnostiikkaa ja hoidon seurantaa erityisesti ongelmatapauksissa, joissa nykyiset diagnostiset kriteerit eivät täyty esimerkiksi hoitoon reagoimattomassa tai varhaisessa keliakiassa.

Tässä tutkimuksessa todettiin ohutsuolen transglutaminaasi-2-spesifisten autovasta-ainekertymien olevan herkkä menetelmä keliakian diagnostiikassa. Seurannan aikana keliakia-autovasta-ainekertymät vähenivät gluteenittomalla ruokavaliolla. Gluteeni keliakiapotilaan ruokavaliossa sai autovasta-ainekertymät ilmaantumaan uudelleen. Kauralla ei tämän tutkimuksen mukaan ollut vaikutusta keliakia-autovasta-ainekertymiin. Ohutsuolen keliakia-autovasta-ainekertymiä määrittämällä voitiin myös hoitoon reagoimattomat keliakiapotilaat erottaa muita suolistotauteja sairastavista potilaista. Lisäksi, alkavassa vaiheessa olevat suolimuutokset voitiin tunnistaa keliakian aiheuttamiksi nykyisiä kriteereitä varhemmin autovasta-ainekertymiä määrittämällä.

Tämän väitöskirjatutkimuksen tulosten perusteella ohutsuolen keliakia-autovasta-ainekertymien määrittäminen auttaa keliakian diagnostiikassa erityisesti potilailla, joilla ohutsuolen koepalalöydöksen ja seerumin vasta-ainetestien perusteella diagnoosi on epävarma.

The diagnosis of coeliac disease is made from a small-bowel mucosal biopsy specimen if villous atrophy with crypt hyperplasia is found on a gluten-containing diet and there is a response to a gluten-free diet. Positivity for serum coeliac antibodies supports the diagnosis. These autoantibodies are targeted to transglutaminase-2 (TG2) and produced in the small intestine. In coeliac disease, deposited autoantibodies have been found in the small-bowel mucosa. The diagnostics of coeliac disease is often problematic in that the quality of a small-bowel biopsy sample is sometimes compromised and villous atrophy is occasionally patchy. Further villous atrophy can also appear in other diseases such as giardiasis, viral infections, food allergies and autoimmune enteropathy. In a minority of coeliac disease patients, small-intestinal damage does not recover on a gluten-free diet. Serum coeliac autoantibodies usually give no additional support in the diagnosis of non-responsive coeliac disease, as most non-responsive patients are serum autoantibody-negative. Gluten-induced small-bowel mucosal villous atrophy is the end stage of the disease and develops gradually from lymphocytic infiltration of the epithelium to crypt hyperplasia and further to villous atrophy. Small-bowel mucosal abnormalities caused by early-stage coeliac disease are unspecific and diagnosis cannot rely on them. The present aim was to assess the value of determinating small-bowel mucosal TG2-specific IgA autoantibody deposits in coeliac disease diagnostics and follow-up, especially in problematic cases. The occurrence of mucosal autoantibody deposits was compared to villous atrophy (I-IV), CD3+ and gamma-delta+ intraepithelial lymphocyte (IEL) densities (I, III, IV) and serum autoantibodies (I-IV).

In studies I-IV, a total of 261 patients had overt and 48 early-stage coeliac disease. In addition, 177 coeliac patients were examined after different periods on a gluten-free diet, and 27 patients evincing no histological response to the diet. Coeliac patients were compared to 86 non-coeliac controls.

Small-bowel mucosal autoantibody deposits were found in all and serum autoantibodies in 91% of overt coeliac patients. Elevated densities of CD3+ and gamma-delta+ IELs were present in 91% and 96% of overt coeliac patients, respectively (I). On a gluten-free diet, after recovery from villous atrophy, the densities of CD3+ IELs and the intensity of autoantibody deposits decreased, eventually also the density of gamma-delta+ IELs, but remained constantly higher than in non-coeliac controls. None of the controls had serum autoantibodies, but 16% had weak autoantibody deposits in the small intestine. In assessment of gluten dependence (II) ten patients underwent a gluten challenge with wheat, barley, rye and oats. Gluten caused villous atrophy and the appearance of small-intestinal autoantibody deposits and serum autoantibodies, in contrast to oats, which had no effect on any of the markers.

Of the 27 non-responsive coeliac patients 21 were on a strict gluten-free diet (III). Of these, 95% evinced small-bowel mucosal autoantibody deposits, although serum autoantibodies were found in only 24%. Increased densities of CD3+ and gamma-delta+ IELs were found in 76% and 71%, respectively. None of the ten controls with other enteropathies had coeliac disease autoantibodies in the serum or deposited in the small-bowel mucosa. Five of the controls had villous atrophy and one third increased densities of IELs.

In early-stage coeliac disease (IV) small-bowel mucosal IgA deposit was found in 96%, serum autoantibodies in 73% and increased densities of CD3+ IELs in 62% and gamma-delta IELs in 71%. In addition, twenty symptomatic early-stage patients with small-bowel mucosal TG2-specific IgA deposits started a gluten-free diet before villous atrophy developed. On a gluten-free diet the autoantibody deposits disappeared and symptoms were alleviated.

The findings showed that determination of small-bowel mucosal TG2-specific IgA deposits is a sensitive tool in finding overt and early-stage coeliac disease. Morphological analysis or IEL densities do not suffice to identify early-stage disease or distinguish different causes of villous atrophy, whereas small-bowel mucosal autoantibodies are accurate in detecting coeliac disease even in seronegative patients. These results together give an opportunity to ascertain or exclude coeliac disease in patients with small-bowel mucosal lesions compatible with coeliac disease but without serum autoantibodies.