“Cannabis is widely used in the United States with an estimated prevalence of 9.5%. Certain cannabinoids in Cannabis sativa, in particular, Δ9-tetrahydrocannabinol (THC), possess immune modulating and anti-inflammatory activity. Depending on the context, the anti-inflammatory activity of cannabinoids may be beneficial, such as in treating inflammatory diseases, or detrimental to normal immune defense against pathogens. The potential beneficial impact of cannabinoids on chronic neuroinflammation has gained recent attention. Monocyte migration to the brain has been implicated as a key event in chronic neuroinflammation and in the etiology of central nervous system diseases including viral infection (e.g., HIV-associated neurocognitive disorder). In the brain, monocytes can contribute to neuroinflammation through interactions with astrocytes, including inducing astrocyte secretion of cytokines and chemokines. In a human co-culture system, monocyte-derived IL-1β due to toll-like receptor 7 (TLR7)-activation, has been identified to promote astrocyte production of MCP-1 and IL-6. THC treatment of TLR7-stimulated co-culture suppressed monocyte secretion of IL-1β resulting in decreased astrocyte production of MCP-1 and IL-6. Furthermore, THC displayed direct inhibition of monocytes, as TLR7-stimulated monocyte monocultures treated with THC also showed suppressed IL-1β production. The cannabinoid receptor 2 (CB2) agonist, JWH-015, impaired monocyte IL-1β production similar to that of THC, suggesting THC is, in part, acting through CB2. THC also suppressed key elements of the IL-1β production pathway, including IL1B mRNA levels and caspase-1 activity. Collectively, this study demonstrates that the anti-inflammatory properties of THC suppress TLR7-induced monocyte secretion of IL-1β, through CB2, which results in decreased astrocyte secretion of MCP-1 and IL-6.
SIGNIFICANCE STATEMENT: As cannabis use is highly prevalent in the United States and has putative anti-inflammatory properties, it is important to investigate the effect of cannabinoids on immune cell function. Furthermore, cannabinoids have garnered particular interest due to their potential beneficial effects on attenuating viral-induced chronic neuroinflammation. This study utilized a primary human co-culture system to demonstrate that the major psychotropic cannabinoid in cannabis, Δ9-tetrahydrocannabinol (THC) and a cannabinoid receptor-2 (CB2) selective agonist, suppress specific monocyte-mediated astrocyte inflammatory responses. In the context of viral-induced chronic neuroinflammation, the findings presented here suggest that cannabinoids via CB2 ligation may have beneficial anti-inflammatory effects.”