Human Autoimmune Thyroid Research Articles

Lymphokine regulation of HLA-DR gene expression in human thyroid cell monolayers.

Studies were conducted to examine the regulation of HLA class II gene expression in human thyroid cells in vitro. Normal human thyroid cells cultured in the absence of lectin or gamma-interferon stimulation lacked detectable HLA-DR cell surface antigen, although low levels of DR alpha-chain-specific mRNA were present. Cyclosporine A, known to inhibit lymphokine production, inhibited basal as well as lectin-mediated increases in levels of DR alpha-chain-specific mRNA and DR surface antigen expression on normal human thyrocytes. Cyclosporine had no effect on the induction of DR antigen gene expression by recombinant gamma-interferon. These data suggested that lectin enhancement of DR antigen expression in human thyroid cells may be mediated by a lymphokine(s) produced in primary human thyroid cell monolayers. This suggestion was confirmed by studies that demonstrated the abrogation of lectin responsiveness by antibody directed against gamma-interferon. Indirect immunofluorescence studies using flow cytometric analyses identified 1.6 +/- 0.2% (mean +/- SD) of cells in primary thyroid cultures as T lymphocytes, a potential source of lymphokine production. Cells derived from thyroid follicular adenomas and carcinomas demonstrated reduced lectin-mediated increases in DR antigen expression compared to normal thyroid cells. DR expression could be enhanced in these lectin-treated cells, however, by T cell coculture. Dose-response studies demonstrated that human thyroid cells were as sensitive to gamma-interferon induction of DR antigen expression as human monocyte/macrophages. These results indicate that human thyroid cell HLA-DR antigen gene expression is sensitive to low levels of lymphokines, such as gamma-interferon; an intrathyroidal T cell population, which may serve as a source of lymphokine(s), remains associated with thyroid epithelial cells in primary thyroid cultures; and lymphokine-thyroid cell interactions may be implicated in the immunopathology of human autoimmune thyroid disease.

AUTOIMMUNE THYROIDDISEASE AND THYROID CELL CLASS II MAJOR HISTOCOMPATIBILITY COMPLEX ANTIGENS

Differences in the immune response to antigenic stimuli, including thyroid autoantigens, have been linked to a group of genes known collectively as the Major Histocompatibility Complex (MHC), which in humans is referred to as the Human Leukocyte Antigen (HLA) complex (Benacerraf, 1981). These genes encode a series of polymorphic cell surface molecules; the class I, 11 & I11 antigens. Classically, class I antigens are expressed on all nucleated cells in the body and are recognized by cytotoxic and suppressor T cells. Class I1 antigens, however, are primarily restricted in their constitutive expression to cells of the immune system and are recognized by the T helper cell subset. Class I11 antigens represent components of the complement pathway. Theories on the aetiology of autoimmune thyroid disease have often invoked a ‘thyroid component’ to such immune responses, but the evidence has been indirect and usually in the form of inherited metabolic abnormalities present in the thyroid cell rather than an immunologically-defined antigen (Wick et al., 1982). However, recent studies on intrathyroidal lymphocyte function have demonstrated the potent role of thyroid antigenic stimulation within the target organ (Totterman et al., 1979; McLachlan et al., 1983; Londei et al., 1984). The finding of MHC class I1 antigens on the surface of the murine thyroid cell (Salamero et al., 1981), and later in human thyroid epithelium (Hanafusa et al., 1983), has focused attention on the generalized facilitation by MHC class I1 antigens in the development of thyroid autoimmunity. This review includes a basic introduction to the class I1 antigens and discusses our present understanding of their involvement in the development of human thyroid autoimmunity.

Cocultures of human thyroid monolayer cells and autologous T cells: impact of HLA class II antigen expression.

Normal human thyroid cells in monolayer culture were induced to express surface HLA class II antigens (DR and DQ) by lectin stimulation. HLA class II positive thyroid cells caused proliferation of autologous T cells, a phenomenon not found in the absence of detectable HLA class II antigen expression. Autologous T cell proliferation was further stimulated by the presence of lectin-free interleukin-2, a known stimulator of activated T cells, and inhibited by monoclonal antibody to HLA-DR antigen. These data demonstrated that normal human thyroid cells, following HLA class II antigen expression, have the capacity to stimulate the immune system. Since over 90% of the monolayer cells were thyrocytes, based on staining with antithyroid microsomal serum, and cells of the monocyte/macrophage series were absent, it is suggested that HLA class II antigen positive human thyroid cells were the principal activators of autologous T cells. Such a mechanism may be important in the target site amplification of human autoimmune thyroid disease in susceptible individuals.

5 Diseases of the TSH receptor

We have reviewed the impact of cellular and molecular biology on our understanding of the immune system and thyroid autoimmune disease and presented the evidence that MHC, TCR and immunoglobulin genes are involved in susceptibility to such disease. At the level of the target thyroid epithelial cell, the identification of the genes for Tg and TPO (the microsomal antigen) using recombinant DNA techniques are evidence of dramatic progress. On the humoral side of the immune response, the investigation of restricted clonality is still hampered by the technical difficulties in obtaining immortal B cell lines producing thyroid antigen specific high affinity IgG antibodies, although the advent of tools to sequence the immunoglobulin V genes from small quantities of DNA will overcome this difficulty (e.g. by polymerase chain reactions). T cells have also begun to be characterized both phenotypically, thanks to the advent of ever better characterized monoclonal antibodies, and functionally at the clonal level, thanks to refinement of cell culture techniques. Future studies in this area will also need to focus on cell immortalization and maintenance of antigen-specific responses although, major strides in the direct sequencing of the TCR are taking place and investigation of T cell receptors in antigen-specific T cells should be feasible. MHC associations with thyroid autoimmune disease, as studied by analysis of RFLP patterns, have not significantly improved already established serological HLA associations and direct MHC gene sequencing will be required. Analysis of the organ-specific regulation of MHC class II gene expression has led to a better understanding of the functional role of MHC class II genes in thyroid autoimmune disease at the target cell level. Such studies have pointed out important local immune responses within the thyroid gland but have not yet provided the initiating factor or factors for human autoimmune thyroid disease in genetically susceptible individuals.