Thymosin peptides and lymphokines do not directly stimulate adrenal corticosteroid production in vitro.

There is developing evidence that certain thymosin peptides and lymphokines produce a transient increase in steroid hormones when introduced systemically. Conversely, the repressive effect of adrenocortical steroids on the immune system is well documented. In the present study, the direct effect of certain components of the immune system on steroid output by rat adrenal fasciculata cells was tested. With this system, there was no direct steroidogenic effect of either the partially purified thymosin fraction 5, or any of the purified peptide components tested (thymosin alpha 1, alpha 7, or beta 4). These peptides also did not synergize the cellular response to ACTH, nor did they induce cAMP production by a ACTH- and NaF-responsive adrenal membrane preparation. Supernatants from Con A-stimulated spleen cells, which were demonstrated to contain lymphokine activity, and partially purified mouse interferon were also without a significant direct or synergistic effect on steroidogenesis by adrenocortical cells. These results suggest that the steroidogenic response to these peptides observed in vivo may be mediated by the central nervous system.