Syngeneic sensitization of mouse lymphocytes on monolayers of thyroid epithelial cells. IX. Thyroid epithelial cells are antigen presenting cells.

We observed T lymphoblast generation after three days of culture of normal spleen lymphocytes on monolayers of syngeneic thyroid epithelial cells. It appears that only these T lymphoblasts sensitized on thyroid monolayers are specifically labelled by fluorescein-conjugated thyroglobulin. In this study, the role of thyroglobulin, and the manner in which it is presented to syngeneic T cells bearing receptors for thyroglobulin were investigated. It appears that thyroglobulin plays a key role in primary syngeneic sensitization of spleen cells in vitro, but its action is not exclusive. Proteins, which are encoded by a gene located in the I-A subregion level of the major histocompatibility complex, are capable of inducing a primary proliferative signal when the presentation of syngeneic class II antigens by syngeneic thyroid epithelial cells is simultaneous. In addition, thyroglobulin-pulsed macrophages are not able to do so. In contrast, once this primary syngeneic T cell proliferation has been accomplished, soluble thyroglobulin is sufficient to induce a secondary response by these syngeneic T cells.