Exposure to morphine affects the expression of endocannabinoid receptors and immune functions.

Compared with control rats, rats under morphine exposure exhibited cannabinoid receptor 2 (CB2-R) upregulation in the spleen and periphery blood mononuclear cells (PBMCs). IgG and IgM values in the plasma were also altered. In morphine abusers, cannabinoid receptors were upregulated in the PBMCs, and the expression of IL-4 mRNA in the PBMCs as well as the IgG and IgM values in the plasma were higher compared with those in healthy people. The expression of cannabinoid receptor 1 and CB2-R in culture cells was directly affected by morphine treatment. These findings indicate that the alteration in cannabinoid receptor expression could be disturbed by morphine exposure, and it may be involved in abnormal immune function.