Adrenocorticotropic hormone controls Concanavalin A activation of rat lymphocytes by modulating IL-2 production

The initiation of DNA synthesis and secretion of Interleukin 2 (IL-2) was m easured in isolated rat splenic lymphocytes following activation with Conca navalin A (ConA). The extent of H-3-thymidine incorporation into activated cells was tested when cultured with various concentrations of Adrenocortico tropic hormone (ACTH), A paradoxical dose-response curve resulted when ACTH caused a biphasic response of augmenting and inhibiting 3H-thymidine uptak e in lymphocytes depending on the hormone concentration. Low levels of ACTH (0,001-1-nM) augmented 3H-thymidine uptake and high levels (10-1000 nM) re versed the effect.. The optimal ACTH concentration was 10 pM ACTH in the pr esence of 5 mu g/ml ConA and there was no ACTH effect on quiescent cells (n o ConA), Conditioned media from splenic lymphocytes treated with various co ncentrations of ConA or ACTH was tested for increased uptake of H-3-thymidi ne by the IL-2 growth dependent Cytotoxic T Lymphocyte Leukemia (CTLL-2) ce lls. ConA conditioned medium could sustain the CTLL-2 cells indicating the presence of IL-2, Conditioned medium from splenic lymphocytes treated with both ConA and 100 pM ACTH fur ther increased CTLL-2 cell proliferation indi cating an additional increase of IL-2 secretion. The identity of IL-2 was c onfirmed by using an anti-rat IL-2 antibody to neutralize the growth potent ial of the conditioned medium. ACTH alone had no effect on the CTLL-2 cell proliferation indicating the effect is due solely to induced IL-2 found in the conditioned medium. IL-2 levels in the conditioned media were quantitat ed by ELISA assay; splenic lymphocytes produced 4.2 ng/ml to ConA only, 19. 2 ng/ml in ConA plus 10 nM ACTH, and no detectable IL-2 at ConA plus 10 uM ACTH. These results demonstrated that ACTH modulates IL-2 secretion from ac tivated lymphocytes, which is both biphasic and concentration dependent. (C ) 2000 Elsevier Science Inc. All rights reserved.