1. genes (extended haplotype (2q33),6 confirming earlier associations. The role played by polymorphic and genes in the development of autoimmune thyroiditis in response to hTg was exhibited in murine experimental autoimmune thyroiditis (EAT), by introducing the permissive transgenes (DR3) and (DQ8) into class II-deficient mice.7 Microsatellite-based, whole-genome linkage studies indicated additional susceptibility loci, such as (6p), (8q), and region 10q for HT and GD, loci (14q), (20q) and region 7q for GD, and locus (12q) for HT.8 The association and linkage of the gene with AITD was confirmed by direct analysis MGC14452 of chromosomal region 8q24.9 Thus, some AITD susceptibility genes may be immune-modifying genes, which increase the general susceptibility to autoimmunity (e.g. locus (2q33).20 Some, at least, of the anti-hTg autoantibodies of healthy subjects may coincide with the immunoglobulin autoantibodies towards a wide range of self antigens, normally found in human serum, and referred to as natural autoantibodies (NAA).21 NAA are produced by self-reactive A-582941 B cells, persisting in the periphery because of positive selection22 and may be implicated in the establishment of peripheral tolerance.21 They are polyspecific and encoded by multiple germ-line variable region genes.23,24 Instead, the anti-hTg autoantibodies from HT patients reach higher titres, are more specific and show increasing degrees of somatic hypermutation, in relation with increasing affinities for hTg.24,25 Both idiotopes uniquely expressed on anti-hTg autoantibodies of HT patients26 and shared by disease-associated and natural anti-hTg autoantibodies have been described.27 On the other hand, A-582941 the production of anti-hTg and anti-TPO autoantibodies often precedes the development of AITD, possibly as a reflection of shared susceptibility genes. The risk of developing hypothyroidism was 43% per year for females with serum thyroid-stimulating hormone levels higher than 6 mU/l and anti-hTg and anti-TPO autoantibodies at titres 1 : 100, and 21% for those having anti-thyroid autoantibodies alone.16 Unfortunately, there are no practical criteria to distinguish between the NAA of healthy individuals, devoid of pathogenic and predictive importance, and the autoantibodies typical of subjects with genetic susceptibility for AITD, or subclinical AITD. Pathogenic role of autoantibodies to human thyroglobulin in AITD As significant titres of anti-hTg autoantibodies are commonly found in euthyroid subjects, their presence does not seem sufficient as a cause of AITD.16 However, cytotoxic autoantibodies against thyrocytes in HT were described.28 In addition, it was reported that the formation of opsonized immune complexes with NAA and complement promoted the uptake and presentation of hTg by antigen-specific and non-specific B cells, and the proliferation of hTg-reactive CD4+ T cells.29 Similar results have been recently reported with AITD-associated anti-hTg autoantibodies, thus establishing a link between autoantibody production and the maintenance A-582941 of AITD.30 Mapping the epitopes of hTg recognized by autoantibodies in human sera Studies with proteolytic, recombinant and chemically synthesized peptides In early studies with hTg proteolytic fragments, epitope recognition by anti-hTg autoantibodies of AITD patients was heterogeneous,31 required the integrity of extended polypeptide chain lengths31,32 and was diminished or abolished by thermal denaturation and reduction, suggesting that autoantibodies recognized mainly conformational epitopes.32 The screening of a bacteriophage expression library of human thyroid cDNA with rabbit anti-hTg antibodies revealed 10 epitope-bearing fragments throughout the hTg length, none of which was recognized by the sera of 10 AITD patients.33 Further screening of this library with rabbit polyclonal antibodies to acetylcholinesterase (AChE) revealed a hTg/AChE shared epitope (residues 2376C2464 of hTg). The autoantibodies binding to this epitope were found in the sera of all eight GD patients, only one of 10 HT patients, and none of eight normal controls.34 Bi-specific anti-hTg and anti-AChE.