Endorphin-like immunoreactivities in uncultured and cultured human peripheral blood mononuclear cells

Abstract

It has been reported that cells of the immune system produce and release considerable amounts of pro-opiomelanocortin (POMC) -derived peptides in response to coculture with a variety of stimulatory agents. The present study investigated whether extracts of human peripheral blood mononuclear cells (PBMC) contain immunoreactivity for β-endorphin (βE) and related peptides. Using four endorphin RIA systems with different specificities, extracts of freshly isolated PBMC and PBMC cultured in the presence or absence of mitogens or of corticotropin releasing factor (CRF) and vasopressin (VP), were analyzed. With a radioimmunoassay (RIA) system directed to the midportion of βE, immunoreactivity (MPβE-IR) was readily detectable, although the concentration was extremely low (ca. 200 pg/10 7 cells). βE immunoreactivity (βE-IR) and α-endorphin immunoreactivity (αE-IR), as determined in C-terminally directed RIA systems, were present in even lower concetrations. γ-Endorphin immunoreactivity (γE-IR) was hardly detectable. Of subsets enriched in T-cells, B-cells or monocytes, the highest concentration of MPβE-IR was detected in extracts of monocytes. Coculture of PBMC with the mitogen Concanavalin A (Con A) or Phytohaemagglutinin (PHA) increased the amount of MPβE-IR in extracts of the cells. No increase in αE-IR, however, was detected, whereas βE-IR was only increased in extracts of cells cultured in the presence of Con A. No increase, in any of the immunoreactivities, was observed in extracts of PBMC cultured with bacterial lipopolysaccharide (LPS) or with the combination of CRF and VP, both stimuli that have been reported to induce POMC peptides in cultured PBMC. The present data show that human PBMC contain endorphin-like immunoreactivity, but in very small amounts. The extremely low concentrations and the ineffectiveness of LPS and the combination of CRF and VP to increase the endorphin-like immunoreactivity raise questions about the reported capacity of PBMC to synthesize POMC-derived peptides.