IgA tTG Research Articles

Gliadin Antibodies in Adult Insulin-Dependent Diabetes - Autoimmune and Immunogenetic Correlates

Gliadin antibody (GA) tests used in screening for coeliac disease (CD) frequently yield positive GA results without accompanying CD in cases of diabetes mellitus type 1 (DM-1). To enlighten this phenomenon we screened 848 DM-1 patients for IgA- and IgG-GA. Subsequently, 16 out of 19 high titre GA patients (6 with CD) were compared with 37 low titre DM-1 patients matched for sex, age and disease duration, for autoimmune and immunogenetic markers. Chronic thyroiditis and thyroid peroxidase (TPO) antibody positivity were more frequent in the GA-positive than in the GA-negative sub-group (38 vs. 2.7%, p=0.003, and 69 vs. 27%, p<0.001, respectively). The tissue transglutaminase (tTg) IgA titres correlated with CD but not with GA. tTg IgG titres were lower in GA-positive individuals (p = 0.0012). GA-positivity correlated with a higher titre of factor XIII IgA antibodies (p < 0.001). GA-positive DM-1 patients were characterised by a distinct immunogenetic profile; the risk of HLA DQB1*02 was lower among GA-positive patients than among GA-negatives (OR 0.4, preventive fraction 0.43). All CD patients were HLA DRBl*03-DQBl*02-positive, but none of the five patients with normal biopsies. GA-positive patients instead had HLA DRB1 * 13 in 37.5% as compared to 8.6% in GA-negative (OR 6.4, etiologic fraction 0.32). Thus, the occurrence of positive GA in DM-1 is correlated to TPO antibody positivity, thyroiditis and factor XIII IgA antibodies, but inversely correlated to tTg IgG, and seems to be associated with another HLA haplotype than that previously found to be associated with CD

Comparison of IgA endomysium antibody and IgA tissue transglutaminase antibody in celiac disease.

The antigen for immunoglobulin (Ig) A endomysium antibody (EmA), a sensitive and specific serological marker for celiac disease, has recently been described as tissue transglutaminase (tTG). The aim of this study was to compare the assays used to measure IgA EmA and IgA tTG antibody in patients with celiac disease and disease control subjects. Sera from 21 patients with untreated celiac disease, 48 patients with treated celiac disease and 128 disease control subjects were tested both for IgA EmA with the use of indirect immunofluorescence against human umbilical cord and for IgA tTG antibody with the use of ELISA. Titres of IgA tTG antibody were significantly higher in both the untreated and treated celiac groups than in the disease control group. Titres in the treated group were, however, significantly lower than in the untreated group. A reference range was calculated to include 99.8% of the disease control group in whom small bowel biopsy showed no evidence of celiac disease. One patient from the disease control group with raised IgA tTG antibody titres and positive IgA EmA was found to have celiac disease on small bowel biopsy. The sensitivity, specificity, and positive and negative predictive values of the IgA EmA assay were all 100%. The sensitivity of the IgA tTG antibody assay was 95%, specificity 100%, positive predictive value 100% and negative predictive value 97.7%. An ELISA used to measure IgA tTG antibody is an excellent tool to screen for celiac disease and may prove useful for monitoring response to treatment.

IgA antibodies to tissue transglutaminase: An effective diagnostic test for celiac disease

Objective: Tissue transglutaminase (tTG) is the main autoantigen recognized by endomysial antibodies. The aim of this study was to assess sensitivity, specificity, and predictive value of IgA and IgG antibodies to tTG in the diagnosis of celiac disease compared with endomysial antibodies. Study design: We established enzyme-linked immunosorbent assay procedures to measure IgA and IgG antibodies to tTG in sera from 48 untreated and 33 treated patients with celiac disease and from 63 patients with gastrointestinal disease who were in a control group. Sera from 10 patients with celiac disease were examined at various times after gluten was reintroduced into the patients’ diet. Results: Both IgA and IgG to tTG were significantly ( P < .001) higher in serum of untreated patients with celiac disease versus those in the control group; IgA but not IgG was significantly ( P < .001) higher in untreated versus treated patients with celiac disease. IgA and IgG antitissue tTG had a diagnostic sensitivity, specificity, and positive predictive value of 92% and 21%, 98% and 97%, and 98% and 83%, respectively. The concordance rate of IgA anti-tTG with IgA antiendomysial antibodies was 95%. In 5 of the 10 patients undergoing gluten challenge, IgA antiendomysium antibodies were detected earlier than IgA anti-tTG antibodies. Conclusions: tTG-based enzyme-linked immunosorbent assay is an effective diagnostic test, although immunofluorescent-based assays are more sensitive, particularly during gluten challenge. (J Pediatr 1999;134:166-71)