In order to determine if the increase in TSPO surface expression on monocytes following activation with LPS was transient, we used a well characterized, potent suppressor of monocyte immune cell activation, Δ9-THC. Briefly, immune cells from lysed, whole blood from HIV+ and HIV− donors were treated with increasing concentrations of Δ9-THC and activated for 48 hours with LPS. Following the activation period, cells were collected and surface stained for CD14 and TSPO. The average TSPO surface expression on monocytes from HIV+ and HIV− donors with indicated concentrations of THC are shown. Data are from 2 independent experiment assessing 6 human donors. (a) indicates significant differences between HIV+ and - donors within respective treatment groups and (b) indicates significant differences within HIV+ and - to their own vehicle control at the p <0.05 level as determined by a two-way ANOVA with an uncorrected Fisher’s LSD. Values are mean ± SEM.