Opioids modulate human neutrophil and lymphocyte function: thermal injury alters plasma beta-endorphin levels

To investigate the role of opioids in the acquired immune dysfunctional state that occurs after burns or trauma, plasma beta-endorphin levels were measured serially in nine severely burned patients, and the effect of four different opioids on normal neutrophil and lymphocyte function was quantitated. The rationale for these studies is that the neuroendocrine system appears capable of interacting with and modulating immune function. The plasma levels of beta-endorphin increased to higher than normal during the first 36 hours after burn (15 versus 3.4 pmol/L, p less than 0.05) but quickly returned toward normal. Morphine had the most profound effect on in vitro neutrophil function; it decreased neutrophil chemotaxis but increased neutrophil bactericidal activity for Staphylococcus aureus, as well as resting and zymosan-stimulated oxygen consumption. Other opioids (naloxone, met-enkephalin, and beta-endorphin) had no direct effect on neutrophil chemotaxis or bactericidal activity. Both naloxone and met-enkephalin increased neutrophil oxygen consumption in a dose-dependent fashion, whereas beta-endorphin impaired neutrophil oxygen consumption. None of the opioids altered resting lymphocyte blastogenesis. The only opioid that impaired the ability of normal lymphocytes to respond to mitogen stimulation at physiologically relevant doses was beta-endorphin. These results, documenting that beta-endorphin levels are altered after thermal injury and that opioids can modulate normal neutrophil and lymphocyte function in vitro, support the concept that changes in neuroendocrine activity may occur and potentially alter immune function.