Morphine upregulates mu opioid receptors of human and monkey lymphocytes

Opioid receptors of subtypes delta, kappa, and mu similar to those found in brain cells have been identified in immune cells. The current study demons trates by competitive polymerase chain reaction the treatment of human lymp hocytic cells with morphine resulting in an increased amount of gene expres sion of mu opioid receptors. Antibodies against the MOR-1, the neuronal mu opioid receptor, were used in Western blot analysis of mu proteins and the results revealed a single band of similar to 50 kDa, the intensity of which was increased by morphine treatment. Similar results of mu opioid receptor activation were observed when monkey lymphocytes were treated with morphin e. These studies suggest that in addition to causing an immune effect throu gh communication with the neuroendocrine system, the psychoactive drug morp hine may modulate immune functions by acting directly on the mu opioid rece ptors expressed on lymphocytes. (C) 2000 Academic Press.