Δ9-Tetrahydrocannabinol and cannabidiol selectively suppress toll-like receptor (TLR) 7- and TLR8-mediated interleukin-1β production by human CD16+ monocytes by inhibiting its post-translational maturation.

Monocytes are innate immune cells that release inflammatory factors upon detection of infectious and injurious stimuli. CD16⁺ monocytes, a subset of the total monocyte population, are associated with acute and chronic inflammation in human immunodeficiency virus-associated neurocognitive disorder and rheumatoid arthritis. Given the role monocytes play in regulating the host immune response, this investigation explored the effects of cannabinoids on the monocyte secretome for potential therapeutic applications. Δ⁹-Tetrahydrocannabinol (THC) and cannabidiol (CBD) are major cannabis-derived compounds established to have immune-modulating properties. Despite a rise in medical cannabis use, the specific mechanism by which THC and CBD modulate the inflammatory response, including by human monocytes remains poorly understood. We hypothesized that THC and CBD suppress toll-like receptor (TLR) 7- or TLR8-induced inflammatory profiles by CD16⁺ and CD16^- monocytes, specifically interleukin (IL) 1β maturation. Cannabinoid receptor 2 selective agonist, JWH-015, was used to deduce whether cannabinoid receptor 2 signaling alone can mimic immune-modulating properties of THC. Primary human CD16⁺ and CD16^- monocytes were pretreated with THC, CBD, or JWH-015 and then activated through TLR7 or TLR8. Activated monocytes mainly produced IL-1β, tumor necrosis factor-⍺, and IL-6. We show that THC and CBD, but not JWH-015, exert anti-inflammatory effects on primary human monocyte apoptosis-associated speck-like protein-incorporating inflammasome formation and subsequent caspase-1 activity, contributing to suppressed IL-1β production. In addition, mRNA expression of IL1B, CASP1, NLRP3, and PYCARD were unaffected by THC. Minimal THC effects were observed on TLR8-mediated AIM2 mRNA expression. Collectively, results from these studies suggest THC and CBD may be useful in mitigating IL-1β-mediated acute or chronic inflammation. SIGNIFICANCE STATEMENT: This current investigation aimed to understand the role of Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) in mediating virally activated CD16⁺ monocyte inflammatory cytokine production. Further, the results indicated that THC and CBD selectively suppress monocyte interleukin 1β production, though THC is more efficacious, through its maturation, as evidenced by suppressed caspase-1 activity and apoptosis-associated speck-like protein-incorporating inflammasome formation. This work provides evidence to support that THC, and to an extent CBD, exert anti-inflammatory effects that could be useful in mitigating monocyte interleukin 1β-mediated chronic inflammation.