Cannabinoid Receptor 2 (CB) Signals via G-alpha-s and Induces IL-6 and IL-10 Cytokine Secretion in Human Primary Leukocytes.

Cannabinoid receptor 2 (CB) is a promising therapeutic target for immunological modulation. There is, however, a deficit of knowledge regarding CB signaling and function in human primary immunocompetent cells. We applied an experimental paradigm which closely models the state of human primary leukocytes (PBMC; peripheral blood mononuclear cells) to characterize activation of a number of signaling pathways in response to a CB-selective ligand (HU308). We observed a "lag" phase of unchanged cAMP concentration prior to development of classically expected Gα-mediated inhibition of cAMP synthesis. Application of G protein inhibitors revealed that this apparent lag was a result of counteraction of Gα effects by concurrent Gα activation. Monitoring downstream signaling events showed that activation of p38 was mediated by Gα, whereas ERK1/2 and Akt phosphorylation were mediated by Gα-coupled βγ. Activation of CREB integrated multiple components; Gα and βγ mediated ∼85% of the response, while ∼15% was attributed to Gα. Responses to HU308 had an important functional outcome-secretion of interleukins 6 (IL-6) and 10 (IL-10). IL-2, IL-4, IL-12, IL-13, IL-17A, MIP-1α, and TNF-α were unaffected. IL-6/IL-10 induction had a similar G protein coupling profile to CREB activation. All response potencies were consistent with that expected for HU308 acting via CB. Additionally, signaling and functional effects were completely blocked by a CB-selective inverse agonist, giving additional evidence for CB involvement. This work expands the current paradigm regarding cannabinoid immunomodulation and reinforces the potential utility of CB ligands as immunomodulatory therapeutics.