Abstract
We have shown that corticotropin (ACTH), alpha-endorphin, and enkephalins can regulate antibody responses, which suggested a role for neuropeptides in a regulatory circuit between the immune and neuroendocrine systems. ACTH and structurally related peptides were examined here for regulation of mitogen induction of the lymphokine gamma-interferon (IFN gamma) in C57BL/6 mouse spleen cell cultures. Synthetic ACTH1-39 and a porcine pituitary extract containing ACTH activity were potent suppressors of the IFN gamma response. Synthetic ACTH1-39 suppressed the response by approximately 62% at 1 to 3 microM, whereas the porcine extract suppressed by greater than 90% at 1 to 3 microM ACTH. The greater potency of the pituitary extract was shown to be due to the presence of an additional peptide of Mr 2100 that was reactive with antibodies to the N-terminal region of ACTH (ACTH1-13), possessed potent anti-cellular activity against L cells and various transformed cells, but lacked ACTH biologic activity. The anti-cellular peptide suppressed the IFN gamma response by greater than 99% at 0.05 microM. The ACTH1-39 cleavage products, alpha-melanocyte stimulating hormone (alpha MSH; acetylated and amidated ACTH1-13), and corticotropin-like intermediate lobe peptide (CLIP; ACTH18-39) had no effect on IFN gamma production. ACTH1-24, like ACTH1-39, has full steroidogenesis activity but also had no effect on IFN gamma production, which suggests a dissociation of the immunoregulatory and steroidogenic properties of ACTH1-39. ACTH1-39, and possibly also the anti-cellular 2100 Mr peptide, is initially synthesized as the precursor polyprotein pro-opiomelanocortin (POMC). Enzymatic processing of POMC, first to the active ACTH1-39 or the anti-cellular peptide and then to the inactive smaller peptides, probably plays an important role in regulation of lymphokine and antibody production by ACTH and ACTH-related neuropeptides. This is consistent with the recent demonstration of the production of ACTH-like peptides by lymphocytes.
