Effects of experimental hyper- and hypothyroidism on numbers of blood mononuclear cells and immune function in rats and guinea-pigs.

A possible effect of thyroid hormones on numbers of mononuclear cells and immune reactivity has been studied in hyperthyroid and hypothyroid guinea-pigs and rats. There were no major changes in populations of blood mononuclear cells in hyperthyroid or hypothyroid animals compared with populations in euthyroid animals. Although there was some evidence for depressed cell-mediated responses to an extract of Candida (monilia) albicans in hyperthyroid rats as assessed by skin tests, this was minor, and responses in tuberculin purified protein derivative (PPD) were normal in all groups, whilst production of macrophage migration inhibition factor in response to PPD and Candida was similar in the three groups of animals. Antibody responses to sheep red blood cells, a thymic-dependent antigen, tended to be depressed in hyperthyroid and hypothyroid rats and increased in hyperthyroid and hypothyroid guinea-pigs, although this was significant only for hyper-thyroid guinea-pigs 16 days after immunization. Responses to trinitrophenol-Ficoll, a thymic-independent antigen, were similar to the three groups of guinea-pigs. Thus, a major effect of excess or deficiency of thyroid hormone on immune responses to foreign antigens has not been demonstrated, although it is possible that immune reactions against thyroid antigens may be more sensitive to the effect of thyroid hormones than responses to foreign antigens.