Identification of distinct sites of beta-endorphin that stimulate lymphokine production by murine CD4+ T cells.
We recently demonstrated that the opioid peptide beta-endorphin (beta-End) has the capacity to stimulate interleukin-2 (IL-2) and IL-4 production by murine CD4+ T cells. Since opioid peptides have been demonstrated to contain stimulatory as well as inhibitory sites, we studied peptide fragments of beta-End to identify a moiety with exclusive stimulatory capacity. To this end, the effects of various opioid peptides on the production of IL-2, IL-4, IL-6, and interferon-gamma (IFN-gamma) by CD4+ T cells were determined. It appeared that two peptide fragments of beta-End, i.e., beta-End6-31 and beta-End18-31, that lack the N-terminal enkephalin part, enhanced IL-2 and IL-4 production to a similar extent as intact beta-End, indicating that the N-terminal part is not involved in the stimulating effects of beta-End. Also the production of IL-6 and IFN-gamma was increased by these peptides. By contrast, the fragments beta-End24-31 and beta-End28-31 did not stimulate the production of the cytokines. Surprisingly, also alpha-End, which is equivalent to beta-End1-16 and hence lacks the sequence comprising amino acids 18 through 31, was stimulatory. This effect was not prevented by naloxone, indicating that opioid receptors were not involved. Moreover, methionine-enkephalin (Met-Enk), which binds to opioid receptors, did not affect cytokine production. Because both alpha-End and beta-End18-31 stimulate cytokine production by CD4+ T cells and do not overlap is sequence, it is concluded that at least two distinct sites of beta-End can exert stimulating effects on cytokine production.
Van den Bergh
P
P
Section of Immunology, TNO-Institute of Ageing and Vascular Research, Leiden, The Netherlands.
Rozing
J
J
Nagelkerken
L
L
D000818:Animals; D001665:Binding Sites; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D004723:Endorphins / Q000737:chemistry / Q000494:pharmacology; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000096:biosynthesis; D007376:Interleukin-2 / Q000096:biosynthesis; D015847:Interleukin-4 / Q000096:biosynthesis; D015850:Interleukin-6 / Q000096:biosynthesis; D008222:Lymphokines / Q000096:biosynthesis*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009270:Naloxone / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D013329:Structure-Activity Relationship; D018822:alpha-Endorphin; D001615:beta-Endorphin / Q000737:chemistry* / Q000494:pharmacology*
D004723:Endorphins; D007376:Interleukin-2; D015850:Interleukin-6; D008222:Lymphokines; D010446:Peptide Fragments; D015847:Interleukin-4; D009270:Naloxone; D001615:beta-Endorphin; D018822:alpha-Endorphin; D007371:Interferon-gamma