EXPRESSION OF THE COSTIMULATORY MOLECULE B7 BB1 IN AUTOIMMUNE THYROID-DISEASE/

Efficient antigen presentation requires the provision of a costimulato ry signal, the best characterized of which is B7/BB1. It is unclear wh ether thyroid cells expressing class II molecules can present autoanti gens to T cells, although this has been suggested as an important mech anism in the initiation of Graves' disease and Hashimoto's thyroiditis . We have found that thyroid cells from patients with thyroid autoimmu nity do not express B7/BB1 in vivo or in vitro, even after activation with the cytokines interleukin-1 or gamma-interferon, or with a phorbo l ester. Increased numbers of CD20(+) B cells and CD14(+) dendritic ce lls expressing B7/BB1 were found in intrathyroidal lymphocyte preparat ions from such patients compared to peripheral blood. These results su ggest that conventional antigen-presenting cells rather than thyroid c ells provide B7/BB1 costimulatory activity in autoimmune thyroid disea se, and argue against a role for the thyroid cells themselves in autoa ntigen presentation to T cells via the B7/BB1 pathway.