Quantification and characterization of ACTH-related peptides produced by human peripheral blood mononuclear cells

We have used a sensitive radioimmunoassay to quantify and characterize PBMC-associated immunoreactive ACTH (ACTH-IR). Mean ACTH content of freshly isolated human PBMCs was 3.8 +/- 0.72 pg (SEM) per 10(6) cells. During 3 days of incubation ACTH-IR in conditioned media of control PBMCs increased significantly, p less than 0.02. Gel filtration chromatography revealed a minor peak of ACTH-IR coeluting with ACTH (1-39) and a major peak coeluting with ACTH (11-24). Treatment with 15 nM CRH did not alter the amount of ACTH-IR secreted or its gel pattern. Synthetic ACTH (11-24), was radioiodinated and was used for binding experiments that demonstrated specific high- and low-affinity binding sites for ACTH (11-24) on a human T cell line. These results add support for a role of ACTH and related peptides in immune regulatory systems and suggest that cell-specific post-translational processing of POMC may generate an expanding number of biologically active moieties.