Experimental evidence pointing to the bidirectional interaction between the immune system and the thyroid axis

Among the many examples of neuroendocrine-immune system interactions the re lationship between the thyroid axis and the immune function has yet to be c learly established. Here we studied the influence of thyroid hormones on th e course of an alloimmune response. Murine T-3 and T-4 levels were found to be increased a few days after the immunization of mice with allogeneic lym phoid cells. Besides in vivo treatment with T3 was shown to increase alloan tibody titers during the early stages of alloimmunization and to enforce ly mphoid proliferation in vitro in a mixed lymphocyte reaction. Conversely, l owering thyroid hormone seric levels by propylthiouracil treatment, negativ ely modulates the humoral and cellular alloimmune responses. The evidence h ere points to the existence of a bidirectional communication between both s ystems. The possibility that the antigenic challenge would increase the thy roid gland activity thus leading to a positive modulatory action upon the i mmune response is also discussed. (C) 2000 International Society for immuno pharmacology. Published by Elsevier Science Ltd. All rights reserved.