Aims: Tissue transglutaminase (tTG) was recently identified as the major autoantigen in coeliac disease. The aim of this multicentre study was to evaluate the impact of a new immunoenzymatic assay for the detection of IgA anti-tGT antibodies. Methods: Seventy four Italian and French clinical laboratories participated in this study; anti-tTG IgA with an enzyme linked immunosorbent assay (ELISA) method using guinea pig liver extract as the coating antigen, anti-endomysium IgA autoantibodies (EMA), and total serum IgA were determined in 7948 patients, 1162 of whom had coeliac disease (737 untreated cases and 425 on a gluten free diet). A proportion of the sera were then sent to a reference laboratory for anti-tTG retesting with an ELISA method using recombinant human tTG antigen. Results: Seven thousand four hundred and fifty eight (93.8%) sera were EMA/antiguinea pig tTG concordant (positive or negative); 490 (6.2%) were non-concordant. The sensitivity of EMA and antiguinea pig tTG in the 737 untreated patients with coeliac disease was 92.1% and 94.8%, respectively, and the specificity was 99.8% and 99.2%, respectively. Retesting of the discordant sera showed that of the 162 sera classified as EMA negative/antiguinea pig tTG positive, only 49 were positive for human recombinant anti-tTG, and that 39 of these were also EMA positive. Furthermore, of the 36 sera classified as EMA positive/antiguinea pig tTG negative, only two were confirmed as EMA positive. Conclusions: The antiguinea pig tTG assay is more sensitive but less specific than EMA, whereas the antihuman recombinant tTG assay is far more specific and just as sensitive as antiguinea pig tTG. Testing for EMA presents considerable interpretative problems and is difficult to standardise.
Autoantibodies against DFS70 (dense fine speckles 70) antigen have recently been identified among antinuclear antibodies (ANA) in patients with various inflammatory diseases and in patients with different types of cancer. These antibodies are recognized using indirect immunofluorescence (IIF) on HEp-2 cells, by a fine speckled nuclear staining in interphase HEp-2 cells and a positive reaction in the chromosome region of mitotic cells. Given that the DFS70 protein is also known as the lens epithelium-derived growth factor, this study was performed with two objectives: (a) to assess the prevalence of these antibodies in patients sent for ANA testing and in 334 patients with different types of neoplasia and (b) to determine whether the lens tissue was a suitable substrate for the detection of antibodies specific to lens proteins. During routine workup for ANA detection by the IIF method, we found 172 DFS70-positive sera among 21,516 consecutive samples (prevalence, 0.8%). In the group of patients with neoplastic disease, 6 of 334 (1.8%) were anti-DFS70-positive. DFS70-positive sera were then assayed by the IIF method on cryostatic sections of mouse eye at a dilution of 1:40 with an anti-human IgG conjugate. Among the 172 DFS70-positive samples detected by the ANA screening, 32 (19%) were strongly reactive against the reticular fibers of the lens; 8 (5%) were positive only to the corneal epithelium (nuclear negative); 5 (3%) were positive both for the cornea and the lens fibers; 13 (7%) stained only the nuclei of lens and cornea cells, and 4 (2%) were positive against the ciliary muscle. Among the patients with neoplastic diseases, only one with lung cancer reacted weakly with the reticular fibers of the lens. Sera from 20 healthy blood donors were negative. In this preliminary study, we have shown that the prevalence of anti-DFS70 antibodies is much lower than previously reported, both in patients screened for ANA and in patients with cancer. We have also seen that some DFS70-positive sera have antibodies that recognize antigens of the lens. Further studies are needed to investigate the fine specificity and the possible significance of these new autoantibodies.
The prevalence of autoimmune thyroid disease in type 1 diabetic patients is higher than in the general population. A routine screening strategy should be implemented with the determination of anti-thyroid antibodies and TSH in type 1 diabetic patients, particularly in girls, and in patients with diabetes of more than 5 years duration. Patients who have positive TPO antibodies may need the assessment of thyroid function at shorter intervals.
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