FUNCTIONAL-ROLE AND SEQUENCE-ANALYSIS OF A LYMPHOCYTE ORPHAN OPIOID RECEPTOR

Pharmacological evidence indicates that lymphocytes express opioid receptors, but this finding has been questioned. By DNA sequencing of reverse transcription-polymerase chain reaction products, we have found that mouse lymphocytes express mRNA encoding an orphan opioid receptor. These mRNA transcripts were detected in the CD4(+), CD8(+), and CD4(-)CD8- lymphocyte subpopulations. Northern blot analysis confirmed that splenic lymphocytes express a 1.5-kb orphan opioid receptor mRNA. Fifteen bases encoding Tyr(71)-Arg(75) in the first intracellular loop are alternatively spliced, suggesting that orphan opioid receptor mRNA encodes two receptor subtypes. Treatment of lipopolysaccharide-stimulated lymphocytes with orphan opioid receptor antisense oligonucleotides suppressed polyclonal IgG and IgM production by 50%. Our results provide direct evidence that lymphocytes express an opioid-like receptor gene, and suggest that this receptor plays a functional role in immunocompetence.