Tissue specificity and serologic reactivity of an autoantigen associated with autoimmune thyroid disease

Association of neutropenia in systemic lupus erythematosus (SLE) with anti-Ro and binding of an immunologically cross-reactive neutrophil membrane antigen

SLE is associated with the production of autoantibodies to self-constituents. In particular, certain ribonucleoprotein particles are targeted. Despite the multitude of autoantibodies produced and the remarkable concentrations of these antibodies in the sera of SLE patients, there have been little data that the autoantibodies found in SLE are involved in the pathogenesis of disease or its manifestations. The present work demonstrates that anti-Ro (or SSA) is associated with granulocytopenia, binds the surface of granulocytes and fixes complement to this membrane surface. Binding is a property of anti-Ro Fab fragments and can be inhibited by 60-kD Ro. However, the antigen bound on the surface of granulocytes is a 64 000 mol. wt protein that is a novel autoantigen in SLE. As suggested by inhibition studies, sequence identity between 60-kD Ro and eight tandem repeats in the 64-kD antigen may be responsible for the observed serologic cross-reactivity. These data imply that anti-Ro antibodies that also bind the 64-kD protein mediate neutropenia in patients with SLE.

T cell responses to orbital antigens in thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is most likely to be a T cell-mediated disease, in which cytokines released in the extraocular muscles activate fibroblasts, increasing glycosaminoglycan production. The nature of the orbital antigen recognized by the infiltrating T cells is unclear, although it is possible that there is cross-reactivity between this and a thyroid autoantigen to explain the close association with thyroid autoimmunity. We have tested the ability of human and porcine eye muscle antigen preparations to stimulate proliferation of circulating T cells from healthy subjects and patients with TAO or Graves' disease without clinical TAO. Occasional responses were seen, particularly after depletion of CD8+ T cells, and two out of 10 TAO patients responded to eye muscle proteins of 25-50 kD after fractionation of antigens on gels and subsequent elution. There was no disease-specific response of T cells to R1, R14, D1 and 1D3, recombinant proteins identified from screening an eye muscle cDNA library with sera from patients with autoimmune thyroid disease. We have also found that interferon-gamma (IFN-gamma) production by T cells from TAO patients was not stimulated by eye muscle membrane antigens or by 1D3. These results suggest that the frequency of circulating T cells responding to eye muscle antigens in TAO is low, and that several candidate orbital antigens, including the 64-kD protein 1D3, are unlikely to be important T cell autoantigens in this condition.

Muscle autoantigens in thyroid associated ophthalmopathy: the limits of molecular genetics

Unlike autoimmune thyroid disease (AITD) in which a number of autoantigens have been identified and characterized, the situation in thyroid associated ophthalmopathy (TAO) is far from clear. A number of candidate antigens have been identified by probing Western blots of orbital tissue (OT) with sera from TAO patients, the most frequently cited being proteins of molecular weight 23, 28, 55, 64, 78 and 120 kilodaltons. In an attempt to identify autoantigens in TAO we have produced a lambda gt11 human eye muscle expression library. This has been screened with sera from four patients with severe TAO whose antibodies bind to one or more of the aforementioned candidate antigens or to a thyroglobulin/acetylcholinesterase (Tg/Ache) shared epitope. Four clones were isolated and characterized; clone R14 encodes the carboxyl terminal 193 amino acids of an IgE binding protein, clones R10 and R13 encode unknown proteins having significant similarity with heat shock protein 27 and the U1 small nuclear ribonucleoprotein respectively. Clone R1 encodes an unknown peptide of 347 amino acids having no similarity with proteins in available data banks. R1 clone affinity purified autoantibodies bind to a protein of Mr 78 kD in a Western blot of porcine eye muscle tissue. Autoantibodies to the R1 recombinant lysogen were clearly demonstrated in 5 of 20 sera from Graves disease patients, its role merits further investigation. The possible relevance of these clones to the pathogenesis of TAO is discussed as well as the limitations of this type of approach in the identification of unknown autoantigens.