Objectives: Production of autoantibodies to the enzyme tissue transglutaminase (tTG) is a hallmark of coeliac disease (CD). We have previously demonstrated that the immumoglobulin (Ig) A response to tTG in adult CD specifically targets its catalytic core region, containing the active-site triad of amino acids. The aim of the present study was to investigate this phenomenon in paediatric patients with CD, and to elucidate the contribution of each active-site residue to epitopes recognised. The specificity of the IgG anti-tTG response was also investigated and compared with that of the IgA anti-tTG response, in both paediatric and adult patients with CD.
Methods: Wild-type and novel variants of tTG were generated via site-directed mutagenesis and expressed as glutathione-S-transferase–fusion proteins in Escherichia coli BL-21. The mutagenic variants of tTG had substitutions of 1, 1, or all of the 3 of the catalytic triad amino acids. All of the recombinant tTGs were tested for their antigenicity in IgA and IgG enzyme-linked immunosorbent assays with cohorts of paediatric (n = 63) and adult (n = 30) CD sera.
Results: Substitution of even 1 amino acid in the catalytic triad resulted in a significant reduction of CD IgA and IgG anti-tTG binding, with all of the mutant proteins displaying diminished antigenicity compared with the wild-type protein.
Conclusions: The core region of tTG is specifically targeted from early on in disease course by CD patient autoantibodies of both the IgA and IgG class.