thymic-factor--circulating and Hyperthyroidism

Topics: Acromegaly; Adolescent; Adult; Child; Diabetes Mellitus, Type 1; Endocrine System Diseases; Growth Hormone; Humans; Hyperthyroidism; Hypothyroidism; Male; Pituitary Neoplasms; Prolactinoma; Thymic Factor, Circulating; Thymus Gland; Zinc

A good body of experimental and clinical evidences suggests that bidirectional interactions do exist between the neuroendocrine system and the thymus activity. In particular, thymic endocrine activity seems to be strongly influenced by neuroendocrine signals. In this context, studies performed in hyper- and hypothyroid subjects and in the low triiodothyronine (T3) syndrome, which affects premature infants, have clearly shown that thyroid hormones and in particular T3 physiologically modulate thymic peptide secretion. In vitro experiments, with thymic whole-organ cultures, have demonstrated that thyroid hormones exert their action on the epithelial cells of the thymus deputed to synthesize and secrete thymic peptides and that such an effect does not seem to depend on the known permissive action of thyroid hormones.

Topics: Adolescent; Adult; Aged; Aging; Female; Humans; Hyperthyroidism; Hypothyroidism; Infant, Newborn; Male; Middle Aged; Thymic Factor, Circulating; Thymus Gland; Thyroid Gland; Thyroid Hormones

The thymus produces humoral factors that induce proliferation and differentiation of T-cells, which are responsible for cell-mediated immunity. Recent data in animals suggest that such thymic hormone activity is modulated by the neuroendocrine network and, in particular, by thyroid hormones, but no information is presently available in humans. To study this question, we measured the circulating thymic factor called thymulin (Zn-FTS) in hyperthyroid and hypothyroid patients. Thymulin levels were higher in hyperthyroid patients than in normal subjects, whereas hypothyroid patients had lower thymulin levels than normal subjects. A significant correlation was found between circulating thymulin and serum T4 and T3 levels. Thymulin changes could be reversed by appropriate treatment in both groups of patients. Recent data indicate that zinc is required to confer biological activity on thymic hormone molecules. This raised the question of whether the influence of thyroid status on thymulin activity could be mediated by changes in serum zinc concentrations. No support for such an explanation was obtained by thymulin measurements by a modified bioassay using an optimal zinc concentration in the assay system. In conclusion, thyroid status modulates thymic endocrine function in humans. Whether and to what extent such modulation is relevant to the function of the immune system remain to be established.

Topics: Adolescent; Adult; Aged; Female; Humans; Hyperthyroidism; Hypothyroidism; Male; Middle Aged; Rosette Formation; Thymic Factor, Circulating; Thymus Gland; Thymus Hormones; Thyroid Gland; Thyroxine; Triiodothyronine