Development of an immunocapture method for measuring IgA antibodies to tissue transglutaminase in the sera of patients with coeliac disease

One of the most reliable sero-diagnostic tests for coeliac disease (CD) is the measurement, by ELISA, of serum IgA antibodies to tissue transglutaminase (tTG) adsorbed to the wells of microtitre plates. In spite of its reliability, however, some discrepancies exist with the results obtained by the antiendomysium histological assay (EMA) and by biopsy the accepted gold standard. Among the reasons for these differences in titres between the ELISA and the last 2 mentioned assays are the conformational changes that proteins undergo on adsorption and the importance of conformational epitopes on tTG for diagnosing CD. To address this problem, a novel procedure was developed using guinea-pig tTG (gptTG) free in solution to interact with IgA antibodies in the sera of CD patients. Any immune complexes so formed are then captured by anti-tTG antibodies preadsorbed to the wells of microtitre plates. This immunocapture method was optimized for the amount of soluble gptTG needed to interact with all the IgA's anti-tTG present in fixed dilutions of serum samples, the amount of rabbit IgG anti-gptTG used to coat the wells of microtitre plates and the order of addition of the reaction components. Comparison of the IgA titres obtained by immunocapture with those by EMA and ELISA (adsorbed tTG) on 9 highly positive and 6 weakly positive sera from clinically characterized CD patients and 5 negative sera from non-CD control subjects revealed that the IgA titres by the immunocapture procedure were well correlated with those obtained by EMA, whereas the titres on ELISA showed discrepancies with both immunocapture and EMA

Comparação dos anticorpos anti-reticulina e antiendomísio classe IGA para diagnóstico e controle da dieta na doença celíaca Comparison of IgA class reticulin and endomysium antibodies for diagnosis and control of the diet in celiac disease

Sensibilidade ao glúten é um estado de elevada resposta iamunológica (celular e humoral) à ingestão de proteínas do glúten do trigo, centeio, cevada e aveia, em indivíduos geneticamente predispostos. A doença celíaca é sua expressão mais freqüente, variando as formas de apresentação. Tem como tratamento a exclusão de alimentos contendo as gliadinas tóxicas. Embora a biopsia do intestino delgado proximal seja necessária, tem-se ressaltado a importância de testes sorológicos no rastreamento, diagnóstico e monitorização da dieta isenta de glúten em pacientes com doença celíaca. O objetivo do presente estudo foi investigar a presença dos anticorpos antiendomísio (EmA-IgA) e anti-reticulina (ARA-IgA) em 56 pacientes celíacos (17 recém diagnosticados; 24 aderentes à dieta; 15 com transgressão à dieta). Os anticorpos foram detectados por imunofluorescência indireta, utilizando como substrato cordão umbilical humano para os EmA-IgA, fígado e rim de rato para os ARA-IgA. Nos pacientes recém diagnosticados e no grupo com transgressão à dieta houve positividade total de 100% para os EmA-IgA e 59,4% para ARA-IgA. Nos pacientes aderentes à dieta nenhum dos anticorpos foi detectado. Dentre os 32 pacientes positivos, a concordância foi de 59,4% (19), sendo que 40,6 % (13/32) eram ARA-IgA negativo e EmA-IgA positivo. Nenhum paciente mostrou-se positivo para os ARA-IgA e negativo para os EmA-IgA. Portanto, a sensibilidade para os EmA-IgA foi de 100% e de 59,4% para os ARA-IgA. A associação dos dois testes não aumentou os índices de positividade total nas amostras. Conclui-se que, atualmente, a pesquisa dos EmA-IgA pode constituir teste sorológico de escolha, seja para diagnóstico, seja para seguimento dos pacientes celíacos, pelo alto valor preditivo, alta sensibilidade e especificidade e relativo baixo custo quando se utiliza cordão umbilical humano como substrato.<br>Sensibility to gluten is a condition with high immunological reaction against gluten proteins from wheat, barley, rye and oats in individuals genetically susceptible. Celiac disease is its most frequent expression with various forms of clinical presentation. The treatment consists in gluten free diet. Although the biopsy of proximal small bowel is necessary, the importance of serological tests is increasing in the screening, diagnosis and monitoring of gluten free diet in celiac patients. The aim of this study was to investigate the presence of antiendomysium (EmA-IgA) and anti-reticulin (ARA-IgA) antibodies in 56 celiac patients (17 at diagnosis, 24 adherent to the diet and 15 with transgression to the diet). The antibodies were detected by indirect immunofluorescence, using human umbilical cord as substrate for the EmA-IgA and rat liver and kidney for the ARA-IgA. In the patients at diagnosis and in the group with transgression to the diet the total positivity was 100% for EmA-IgA and 59.4% for ARA-IgA. Antibodies were not detected in gluten-free diet patients. Among the 32 positive patients, the concordance of both tests was of 59.4% (19/32), being 40,6% (13/32) negative to ARA-IgA and positive to EmA-IgA. No patient was positive for ARA-IgA and negative for EmA-IgA. Thus, the sensitivity for EmA-IgA was of 100% and 59,4% for ARA-IgA. The association of the two tests did not improve the positivity in the samples. In conclusion, EmA-IgA can be considered the best serological test for diagnosis and follow up of celiac patients, because it presents high predictive value, high specificity and sensibility and is not expensive if using human umbilical cord as substrate