IgG anti-tTG responses in different autoimmune conditions differ in their epitope targets and subclass usage

•Coeliac disease IgG anti-tTG epitopes are shared with those of the coeliac disease IgA anti-tTG response.•Epitopes recognised by coeliac disease IgG anti-tTG differ from those of IgG anti-tTG in other autoimmune conditions.•IgG anti-tTG subclass usage in coeliac disease and Type 1 diabetes mellitus is predominantly IgG1.•The IgG anti-tTG response was more frequently composed of IgG2–IgG4 antibodies in non-coeliac IgG anti-tTG positive individuals.