Thyroid function and immune reactivity during metamorphosis in Xenopus laevis, the South African clawed toad

High plasma titers of thyroid and adrenocorticoid hormones are present during the metamorphosis of Xenopus laevis. Here we examine the influence of thyroid hormones on several features of immune reactivity during this period, e.g., the capacity of thymus-derived immunocytes to reduce (immune suppression) or amplify (helper function) antibody production. Further, we test whether thyroid hormone is able to modulate the expression of putative interleukin 2 (IL-2) receptors on lectin-activated adult Xenopus splenocytes, an aspect of helper function. Finally, we have tested the ability of thyroid hormones to affect larval antibody-producing cells directly. Our data suggest that all three functions (suppressor, helper, and antibody producing) are independent of thyroid function during metamorphosis. However, the anatomical distribution of two features of immune suppression, as well as the numbers of lectin-activated splenocytes able to bind anti-IL-2 receptor antibody, were changed by thyroid function. In vivo thyroid blockade by thiourea prevented the transition from the premetamorphic to the adult pattern of distribution of the two suppressor functions; triiodothyronine in vitro stimulated an increase in the numbers of cells able to bind an IL-2 receptor antibody.