Identification of mu-opioid receptor epitopes recognized by agonistic IgG

Autoantibodies to the delta-opioid receptor function as opioid agonists and display immunomodulatory activity

In this report, we show that affinity purified human anti-delta opioid receptor (DOR) autoantibodies from IVIG are specific to DOR and possess agonistic properties displayed by their ability to dramatically decrease forskolin stimulated cAMP accumulation. Anti-DOR autoantibody also caused phosphorylation of the opioid receptor. Anti-DOR autoantibody treatment showed a significant reduction in CXCR4 gene expression as well as surface protein expression. In contrast, anti-DOR autoantibody treatment significantly upregulated CCR5 gene and protein expression. The presence of anti-DOR autoantibodies in IVIG and their potent immunomodulatory activity is further evidence to support the cross-talk between the neuroendocrine and immune systems.

Anti-mu-opioid-receptor IgG antibodies are commonly present in serum from healthy blood donors: evidence for a role in apoptotic immune cell death

We previously observed the presence of anti-human mu-opioid-receptor (anti-hMOR) autoantibodies in IgG pools prepared from several thousand healthy blood donors. These autoantibodies behaved agonistically because of their ability to bind to the first and third extracellular loops of the receptor. In this study, we found that each healthy donor's serum contained anti-hMOR IgG autoantibodies with a specific activity against both the first and the third extracellular loops of the receptor. Because of the inability of IgG to cross the blood-brain barrier, we investigated the effects of the expression of anti-hMOR autoantibodies on immune cells. In analogy to studies of the effects of morphine, we investigated the ability of antibodies to sensitize splenocytes to Fas (CD95)-mediated apoptosis. We took advantage of the high sequence homology between murine MOR and hMOR extracellular loops to estimate the effect on murine splenocytes of anti-hMOR antibodies raised by immunizing mice. Splenocytes from mice injected with Chinese hamster ovary (CHO) cells expressing MOR were sensitized to Fas-mediated apoptosis, whereas those from mice injected with CHO cells or phosphate-buffered saline were not. Similar sensitization to Fas-mediated apoptosis was observed in splenocytes from mice undergoing passive transfer either with IgG from mice previously immunized against CHO cells expressing MOR or with IgG directed against the first and third extracellular loops of the receptor. Together, our data show that anti-MOR autoantibodies are commonly expressed in healthy humans and could participate in the control of lymphocyte homeostasis by promoting Fas-mediated apoptosis.