On the localization of effector cells in cyclosporin-induced autoimmunity

Lethally irradiated rats, reconstituted with syngeneic bone marrow and given Cyclosporin A (CyA) for 6 weeks, developed disease resembling allogeneic graft-versus-host disease 2 weeks after withdrawal of CyA. Other studies have demonstrated the pivotal role of the thymus in the etiology of this CyA-induced autoimmune disease (CyA-AI). In this study the question was addressed whether inducer/effector cells of CyA-AI are generated in the thymus during or after CyA administration; whether these cells stay in the thymus, or, if they don't, whether they home to the secondary lymphoid organs. Adoptive transfer of thymocytes from donors treated for induction of CyA-AI obtained one and 14 days after cessation of CyA administration did not elicit CyA-AI in irradiated secondary recipients. Furthermore, adult thymectomy of rats immediately after the course of CyA did not influence the kinetics of development of skin pathology, although weight loss commenced later in thymectomized than in sham-thymectomized rats. Lymph node and spleen cells obtained from donors treated for induction of CyA-AI one and 14 days after withdrawal of CyA-AI caused CyA-AI upon adoptive transfer to secondary recipients, but the symptoms of acute disease (dermatitis, alopecia and weight loss) were strikingly less severe upon transfer of lymphoid cells obtained one day after stopping CyA than 14 days thereafter. Therefore, this study demonstrates that CyA-AI inducer/effector cells are generated in the thymus during the administration of CyA. These cells exit from the thymus during CyA administration; either they home predominantly peripherally (i.e. in the skin) rather than in the secondary lymphoid organs, or they leave the thymus as inducer cells which home in the lymphoid organs where they subsequently may trigger potentially autoreactive lymphocytes as probably also present in normal individuals, or both pathways may be operative.