A hallmark of human immunodeficiency virus (HIV) infection is chronic immune activation and is believed to be one of the major contributors to neuroinflammation and HIV-associated neurocognitive disorder (HAND). Circulating activated monocytes, including those that are CD16⁺, have been implicated in HIV-associated neuroinflammation. These activated monocytes become infected with HIV in the periphery, cross the blood-brain barrier (BBB) and release inflammatory factors, HIV virions and viral proteins. These factors lead to HIV infection and activation of brain-resident cells, including microglia and astrocytes, driving a pro-inflammatory environment in the brain. Ultimately, these processes contribute to neuronal dysfunction and death, ultimately resulting in cognitive decline in up to 50% of the HIV-infected population. Cannabis is widely used by the HIV-infected population at an estimated prevalence of 23-56% in the United States. [Delta]2079-Tetrahydrocannabinol (THC) and cannabidiol (CBD), two major constituents of cannabis, are known to have immune suppressive and anti-inflammatory properties. The overall objective of this project was to determine whether the cannabinoids, THC and CBD, could suppress monocyte activation and monocyte-mediated astrocyte inflammation, which are key processes implicated in chronic neuroinflammation and HAND. Herein, it is shown that HIV-infected donors using cannabis displayed a lower level of circulating activated (CD16⁺) monocytes and plasma IP-10 compared to non-using HIV-infected donors. Furthermore, in vitro studies revealed that THC but not CBD suppressed monocyte expression of CD16 and secretion of IP-10, suggesting that THC is the major cannabinoid in cannabis promoting the anti-inflammatory effects. To determine whether activated monocytes could promote inflammatory functions of brain-resident glial cells, we developed a human co-culture system utilizing primary monocytes and cell-line/primary fetal astrocytes with viral-related stimulators (IFNa a0333nd a TLR7 agonist - R837). Monocytes, together with IFNa a0333nd/or R837, promoted astrocyte secretion of MCP-1, IL-6 and IP-10. Furthermore, monocyte-derived IL-1v0333 was critical for astrocyte secretion of pro-inflammatory factors, as neutralization of IL-1v0333 strongly hampered the astrocyte response, while direct addition of recombinant IL-1v0333 to astrocyte monocultures mimicked the actions of monocytes. In vitro THC treatment of the R837-stimulated co-culture resulted in decreased astrocyte production of MCP-1 and IL-6, while CBD increased IL-6 production and had no effect on MCP-1 production. With the use of separate monocyte and astrocyte monocultures, THC and CBD were shown to directly target both cell types. Interestingly, THC and CBD were both shown to decrease the percent of astrocytes producing IL-6 and MCP-1, which for THC, is concordant with the co-culture observation. However, the CBD-mediated decrease in IL-6 and MCP-1 production in the astrocyte monoculture differed from the observations in the CBD-treated co-culture. Our findings were explained when THC and CBD were shown to suppress and augment monocyte production of IL-1v0333, respectively. Furthermore, the CBD-mediated augmentation of monocyte-derived IL-1v0333 was able to override the direct CBD suppression on the astrocytes. Collectively, THC but not CBD, impairs monocyte activation and monocyte-driven astrocyte inflammatory responses. In the context of HAND, cannabis use, in particular THC, may decelerate monocyte processes that are implicated in neuroinflammation and cognitive dysfunction.
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