IgG1 antiendomysium and IgG antitissue transglutaminase (anti-tTG) antibodies in coeliac patients with selective IgA deficiency

Abstract

Background - In selective IgA deficiency (IgAD), there is no reliable screening test for coeliac disease (CD). Aims - To evaluate the usefulness of IgG1 antiendomysium and IgG antitissue transglutaminase tests for CD diagnosis in IgAD. Methods - IgA and IgG antigliadin antibodies (IgA- and IgG-AGA), IgA and IgG1 antiendomysium antibodies (IgA- and IgG1-EMA), and IgA and IgG antitissue transglutaminase (IgA- and IgG-antitTG) were assayed in: (a) 20 untreated IgAD/CD patients; (b) 34 IgAD/CD patients on a strict gluten free diet (GFD); (c) 10 IgAD/CD patients not on a strict GFD; (d) 11 untreated CD patients without IgAD; (e) 10 healthy IgAD patients; and (f) 25 healthy controls. Results - In all untreated IgAD/CD patients, IgG1-EMA, IgG-anti-tTG, and IgG AGA were positive whereas IgA antibodies against these antigens were negative. IgAD/CD patients on a strict GFD did not produce IgG-AGA or IgG1-EMA but four of 34 produced IgG anti-tTG. IgAD/CD subjects not on a strict GFD produced IgG-AGA whereas 5/10 and 4/10 were IgG1-EMA and IgG-anti-tTG negative, respectively. Untreated CD patients without IgAD were AGA (IgA and IgG), EMA (IgA and IgG1), and anti-tTG (IgA and IgG) positive. Healthy controls were AGA and EMA negative whereas two of 10 apparently healthy IgAD subjects and one of 25 healthy negative control were IgG-anti-tTG positive. Conclusions - Both IgG1-EMA and IgG-anti-tTG tests appear to be useful for identification of IgAD/CD patients whereas they are less satisfactory for monitoring dietary compliance in these subjects. In addition, our findings seem to suggest that IgG-EMA autoantibodies produced by coeliac patients are mainly of the IgG1 subtype.