THE HUMORAL ACTIVITY OF THE AVIAN THYMIC MICROENVIRONMENT

The thymic microenvironment (composed of the lympho-epithelial stroma and the secretory products of the thymic epithelium) provides the requ ired milieu for the development of the thymus-derived lymphocytes (T c ells). There is limited information characterizing or identifying the active secretory components of the avian thymus. The work discussed he re has focused on examination of the presence, regulation, and activit y of one of the thymic hormones (thymulin) in the chicken. A thymulin- like product has been shown to exist in chicken serum as assessed by t he mammalian bioassay and an ELISA immunoassay; thymectomy removes thi s product from the serum. Serum thymulin activity has been shown to be directly related to the thyroid status of the chick with the function ally hypothyroid Cornell sex-linked dwarf strain having lower levels t han the euthyroid K strain. Alterations in circulating thymulin concen trations produced by daily thymulin injections resulted in an altered profile of the major peripheral blood T cell subpopulations and produc ed significant changes in the autoimmune pathology present within the Obese strain chicken. These approaches represent preliminary attempts to study the role of thymulin in avian immune development and in immun e-neuroendocrine interactions.