Somatic hypermutation in autoimmune thyroid disease

Autoimmune thyroid disease is one of the most common autoimmune diseases. There is typically patient antibody (Ab) reactivity to one or more of the antigens thyroglobulin (Tg), thyroid peroxidase (TPO) and the thyroid simulating hormone receptor (TSHr). With the advent of combinatorial library technology, there has been an enormous increase in the number of sequences from Ab to Tg and TPO. The repertoire of both Tg and TPO Ab is restricted and indicates the importance of somatic hypermutation in the development of the high affinity Ab response. However, there are still too few sequences to determine patterns in which the mutation occurs, which residues are introduced during substitution and how individual substitutions affect the affinity of the Ab. Ab to the TSHr are of far greater pathological significance than those to Tg and TPO, but the current repertoire of Ab to the TSHr has yet to include the high affinity IgG Ab characteristic of patient serum Ab. Instructive analysis of the role of somatic hypermutation in the development of TSHr Ab therefore still awaits the isolation of the pathologically active repertoire. Despite this, the Ab response in thyroid autoimmunity remains one of the best characterised of human autoimmune diseases.