We cloned activated T cells from thyroid tissue of patients with autoimmune thyroid disease. After separation on 40% Percoll gradients, T cells were cultured for 2-7 days with T cell growth factor (interleukin 2; 20 U/mL) and cloned by limiting dilution (0.3 cells/well) in the presence of irradiated autologous peripheral blood mononuclear cells (PMC; 10,000/well) as feeder cells. Fifty-seven clones were successfully expanded and tested for reactivity, cytotoxicity, helper/suppressor function, and phenotype. In the reactivity assays clones were tested for responses to autologous and allogeneic PMC, thyroid cells, human thyroglobulin (hTg), and microsomal antigen. Two distinct patterns of functional T cell clones emerged from these characterization studies. Seventy-five percent of T cell clones recovered from Graves' disease thyroid tissue (n = 21) were of helper-induced (CD4+/4B4+) phenotype, and most were effective immunoglobulin helper clones. Fifty percent of Graves' T cell clones responded to autologous PMC, and 33% had a proliferative response to autologous thyroid cells. No cytotoxic clones were derived from Graves' thyroid tissue. By contrast, intrathyroidal T cell clones from patients with autoimmune thyroiditis (n = 36) were 59% suppressor/cytotoxic (CD8+) phenotype, 17% suppressed immunoglobulin secretion, and 55% were cytotoxic to allogeneic blast cells. Fifty-five percent of clones also responded to autologous PMC, and one clone was nonspecifically autocytotoxic. In the thyroid antigen proliferation assays 11% of thyroiditis clones reacted to human thyroglobulin, but none responded to microsomal antigen. Two clones were cytotoxic to autologous but not allogeneic thyroid cells. These data demonstrate that the majority of intrathyroidal T cells in autoimmune thyroid disease are autoreactive. However, small numbers of thyroid-specific T cell clones are present within the thyroid of such patients; they are principally helper-inducer T cells in Graves' disease thyroid and cytotoxic T cells in autoimmune thyroiditis.

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.

T lymphocytes possessing helper function produce soluble factors that greatly augment B-cell proliferation and differentiation into antibody-secreting cells. In humans the subset of T lymphocytes bearing the T4 surface antigen comprises most of the cells that display helper activity and recognize class II antigens of the major histocompatibility complex (MHC), while the subset bearing the T8 antigen comprises T cells recognizing class I MHC antigens and exhibiting cytotoxic or suppressor function. Monoclonal antibodies to T4 or T8 greatly inhibit the cognitive and effector function of cells with the corresponding phenotype. This function/phenotype correlation is not absolute, however, for there are many examples of T8-positive clones that recognize MHC class II antigens and have helper activity, as well as of T4-positive clones with suppressor or cytotoxic function. Recently a family of cell-surface neoantigens, which might be relevant to T-cell function and which are present on activated but not on resting T lymphocytes, has been identified in mouse and humans using monoclonal antibodies. Some of these antibodies block the cytolytic activity of alloreactive T-cell clones, suggesting the possible involvement of such molecules in the activation of cytotoxic T-cell clones or in the lytic process itself. We now describe a similar late-differentiation antigen (LDA1) that is expressed by human T lymphocytes only following activation and is recognized by a monoclonal antibody that inhibits the antibody-inducing helper function of T lymphocytes.

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Abstract. An association exists between certain MHC polymorphisms and autoimmune thyroid disease in animals and humans. The observation of MHC class II antigen expression by the thyroid suggests that such associations may have mechanistic explanations at the level of the thyroid cell. Such class II antigen expression, rather than being a constitutive property of thyroid epithelium, appears to be primarily mediated by lymphokine secretion from intrathyroidal T lymphocytes and a variety of agents, for example TSH and TSH receptor antibodies, may amplify such lymphokine action. Thyroid cell class II antigens participate in activation and amplification of T cells and are involved in presentation of thyroid antigen to the immune system. The relationship between these local immune interactions and the initial events leading to the development of autoimmune thyroid disease requires a more fundamental understanding of the workings of the immune system at the site of antigenic stimulation.