Immunomodulatory activity of met-enkephalin and its two potent analogs

The effects of Met-enkephalin (Met-Enk), a delta receptor binding opioid peptide, and its more stable synthetic analogs, Tyr-d-Ala-Gly-MePhe-Met-NHC₃H₇-iso (1), Tyr-d-Ala-Gly-MePhe-Gly-NHC₃H₇-iso (2) and Tyr-d-Ala-Gly-McPhe-Gly-NHCH₂C₆H₅ (3), on human T-cell transformation and natural killer (NK) cell cytotoxicity have been evaluated. Analogs 1 and 2 have been found to be as potent as Met-Enk in stimulating T-cell transformation and augmenting NK cell cytotoxicity. Analog 3 had no effect on T-cell transformation and NK cell cytotoxicity. Proliferative response was measured by ³H-thymidine uptake after 5 days of incubation. The kinetics of the T-cell transformation response (peak 5th day) is similar to those for in vitro T-cell responses to specific antigens rather than via polyclonal activation.