Identification of distinct sites of beta-endorphin that stimulate lymphokine production by murine CD4+ T cells
Van den Bergh, P.; Rozing, J.; Nagelkerken, L.
Lymphokine and Cytokine Research 13(2): 63-69
1994
ISSN/ISBN: 1056-5477 PMID: 7914752 Document Number: 426738
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-End-6-31 and beta-End-18-31 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-End-24-31 and beta-End-28-31 did not stimulate the production of the cytokines. Surprisingly, also alpha-End, which is equivalent to beta-End-1-16, 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-End-18-31 stimulate cytokine production by CD4+ T cells and do not overlap in sequence, it is concluded that at least two distinct sites of beta-End can exert stimulating effects on cytokine production.