Affinity maturation of immunoglobulin A anti-tissue transglutaminase autoantibodies during development of coeliac disease

Abstract

SummaryCoeliac disease (CD) is an immune-mediated enteropathy triggered by ingestion of wheat gluten and related cereals in genetically predisposed individuals. Circulating immunoglobulin A (IgA) class autoantibodies against tissue transglutaminase (IgA-TGA) are highly specific and sensitive serological markers for CD, which is ultimately confirmed by duodenal biopsy. Although CD is considered a life-long disorder, transient or fluctuating IgA-TGA seropositivity has been observed in asymptomatic individuals on a glutencontaining diet. We set out to explore possible differences in the maturation of IgA-TGA avidity between individuals progressing to CD and subjects remaining healthy despite occasional expression of autoantibodies. We developed a time-resolved fluorometric IgA-TGA assay based on human recombinant tissue transglutaminase (tTG), and further modified the method to also measure urea-dependent avidity of the autoantibodies. We measured the autoantibody titres and avidities of sequential serum samples from 10 children developing CD and 10 children presenting transient or fluctuating autoantibodies. Both the initial titres at seroconversion and peak values of transient/fluctuating IgA-TGA were significantly lower than corresponding autoantibody titres in samples drawn from individuals with progressing CD (P = 0·004 and P = 0·0002, respectively). However, there were no statistically significant differences in the initial or peak avidity index values between the two groups of children. The avidity index values increased during the follow-up period (P = 0·013 for both groups) with no significant difference in the rate of avidity maturation between children with transient/fluctuating IgA-TGA and children developing CD. According to our results, high autoantibody titres have a higher predictive value than avidity maturation of TGA-IgA in screening for CD.

Serum autoantibodies directed against transglutaminase-2 have a low avidity compared with alloantibodies against gliadin in coeliac disease

“…As shown in Fig. 3, we did not observe a relation between antibody avidity and concentration, similar to previous reports [11,13]. In addition, we titrated the NaSCN concentration and chose 1 M as the optimal concentration, leading to the distinctive capacity between high-and low-avidity antibodies.…”

“…However, it should be considered that in this study we measured an average avidity of antibodies with a wide range of affinities, as it is a polyclonal B cell response [25,33]. This may also be the reason for the large variation in avidity that we observed, as has also been seen by others [11]. It could, of course, be the case that the observed range in avidity reflects differences in B cell responses between, or even within, patients.…”

“…In the scenario where TG2-specific T cells are not involved, one could speculate that help from gliadinspecific T cells may not be as efficient, and consequently the affinity maturation of the antibody may therefore be less efficient [8,9]; this may lead to an antibody pool with lower avidity. Information on the avidity of antibodies may provide insight into the development or even pathogenicity of the immune response [10,11].…”

Anti-transglutaminase antibodies in non-coeliac children suffering from infectious diseases

“…Anti‐tTG were captured by human recombinant transglutaminase bound in enzyme‐linked immunosorbent assay (ELISA) plate wells that were used for the measurement of anti‐tTG. After two washing rounds, low‐avidity antibodies were eluted by incubating the wells with 120 µl of PBS solution containing 5 M urea, pH 8·0, for 20 min at room temperature (RT) [11]. The control wells were treated with PBS alone for the determination of reactivity values.…”

Predictors of autoimmune disease: Autoantibodies and beyond

“…In this disease, autoantibodies of the IgA isotype are usually the most diagnostic. Rising autoantibody titers are more predictive than avidity maturation of the IgA antibody to transglutaminase in screening for celiac disease [60].…”