Participation by opioids in the immunostimulatory activity of myelopeptides.

Bone marrow myelopeptides (MP), besides having immunostimulatory activity, had a pronounced dose-dependent effect on the development of pain sensitivity in mice. Nanogram amounts of MP evoked a hyperalgesic response and increased antibody formation to sheep red blood cells three to nine times. Milligram amounts of MP had a hypoalgesic effect and did not affect antibody response.