CANNABINOID RECEPTORS CB1 AND CB2 - A CHARACTERIZATION OF EXPRESSION AND ADENYLATE-CYCLASE MODULATION WITHIN THE IMMUNE-SYSTEM

Cannabinoid receptor (CB) expression was characterized in immunologica l cell and tissue preparations. Northern analysis revealed similar to 6-kb transcripts for CB1 (brain-type) in mouse spleen and brain and in rat cerebellum. CB1 was not detected in mouse thymus or rat spleen RN A by Northern analysis. CB2 (peripheral) was detected as a similar to 4-kb transcript in mouse spleen and thymus and as similar to 2.4-kb tr anscripts in rat spleen. Quantitation of CB2 transcripts in mouse sple en and thymus revealed similar to 4 x 10(3) and similar to 4 x 10(2) m olecules/100 ng RNA, respectively, with no quantifiable CB2 in mouse b rain. Conversely, CB1 was expressed in mouse brain (similar to 2 x 10( 5) molecules/100 ng RNA) with lower expression in mouse spleen (simila r to 2 x 10(2) molecules/100 ng RNA) and was not quantifiable in mouse thymus. Competition binding in intact mouse splenocytes demonstrated that nonradiolabeled cannabinoids CP-55940, Win-55212-2, CP-56667, Del ta(9)-THC, and cannabinol all competed for receptor binding with H-3-C P-55940, a high-affinity nondiscriminating CB1 and CB2 receptor ligand . Based on previous findings which demonstrated a marked inhibition of T-cell-dependent immune responses by cannabinoids, primary T cells an d several T-cell lines were characterized. Radioligand binding analysi s identified 100-300 cannabinoid receptor binding sites/cell with an a pproximate K-d of 200-700 pM in purified splenic T cells which also ex hibited cannabinoid-induced inhibition of adenylate cyclase, Northern analysis of human T-cell lines revealed similar to 2.4-kb CB2 mRNA tra nscripts but no CB1 in HPB-ALL cells, a cell line which also exhibited inhibition of adenylate cyclase by Delta(9)-THC. Conversely, Jurkat E 6-1 cells expressed an unusual mRNA banding pattern for CB2 expressing three distinct transcript sizes, none of which were 2.4 kb, the size for human CB2. Jurkat also did not express CB1 mRNA and did not exhibi t inhibition of adenylate cyclase when treated with Delta(9)-THC. Coll ectively, these results provide further evidence that CB2 is the predo minant cannabinoid receptor within the immune system and that this for m of the receptor is expressed on T cells. (C) 1997 Academic Press.