The humoral activity of the avian thymic microenvironment.

The thymic microenvironment (composed of the lymphoepithelial stroma and the secretory products of the thymic epithelium) provides the required milieu for the development of the thymus-derived lymphocytes (T cells). There is limited information characterizing or identifying the active secretory components of the avian thymus. The work discussed here has focused on examination of the presence, regulation, and activity 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 the mammalian bioassay and an ELISA immunoassay; thymectomy removes this product from the serum. Serum thymulin activity has been shown to be directly related to the thyroid status of the chick with the functionally hypothyroid Cornell sex-linked dwarf strain having lower levels than the euthyroid K strain. Alterations in circulating thymulin concentrations produced by daily thymulin injections resulted in an altered profile of the major peripheral blood T cell subpopulations and produced 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 immune-neuroendocrine interactions.