ANTIBODY TO GP39, THE LIGAND FOR CD40 SIGNIFICANTLY INHIBITS THE HUMORAL RESPONSE FROM GRAVES THYROID TISSUES XENOGRAFTED INTO SEVERE COMBINED IMMUNODEFICIENT (SCID) MICE

Experimental evidence suggests that interference with gp39-CD40 intera ctions may have therapeutic potential in prevention of certain autoimm une disorders (i.e., collagen-induced rheumatoid arthritis). The bindi ng between CD40 expressed on mature B cells and CD40 ligand (CD40L, gp 39) transiently expressed on activated T helper cells (Th) further sta bilizes the interactions (between Th and B cells) and coordinates the responses of the interacting cells during antigen presentation, and is essential for thymus-dependent humoral immunity. Graves' disease is t he most common form of hyperthyroidism, in which hyperactivity of the thyroid gland is due to an autoantibody directed against the thyrotrop in receptor (TSHR). The main objective of our study was to determine t he role of interactions between gp39 and CD40 in ''an established'' hu man Graves' disease (GD). Severe combined immunodeficient (SCID) mouse served as a vehicle for human Graves' thyroid tissue. This experiment al setting allows us to study, observe, and immunomodulate human autoi mmune tissue in so called in vivo condition. We studied the effects of ip administration of anti-gp39 mAb on humoral response, thyroid funct ion tests, expression of adhesion molecules, and HLA-DR on human thyro cytes and histopathological changes from human GD thyroid tissue xenog rafts. GD thyroid tissue from 4 patients was xenografted into 20 SCID mice (0.8 g/mouse). Human immunoglobulin G (IgG) levels became detecta ble in SCID mice 1 week after xenograftment. Ten SCID mice were sequen tially administered anti-gp39 mAb (250 mu g/mouse/dose) ip every 4 day s until the end of the experiment. Ten control animals were injected w ith vehicle (PBS) in similar fashion. Blood samples were taken every 2 weeks from the tail veins for measurement of the humoral response [hu man IgG, thyroid-stimulating antibody (TSAb), antithyroperoxidase (ant i-TPO), and antithyroglobulin (anti-Tg) Abs], and thyroid function tes ts. After 8 weeks, animals were sacrificed and thyroid tissue was exam ined histologically. The humoral response from the intrathyroidal lymp hocytes was measured and the tissue morphology of GD was preserved dur ing the 8-week period in phosphate-buffered saline (PBS)-treated SCID mice xenografted with GD xenografts. However, administration of anti-g p39 mAb completely blocked or significantly decreased the humoral resp onse in all heated animals. On the other hand, no significant histolog ical changes were associated with the administration of anti-gp39 mAb. The degree of lymphocytic infiltration in thyroid tissue xenografts w as comparable in both groups. Serum thyroxine values were normal in bo th groups. In spite of a profound immunosuppressive effect on the humo ral response by directly blocking CD40-gp39 interactions in vivo, this did not result in complete deletion of the responding Th in the thyro id specimens.