Alcohol use disorder (AUD) is associated with enhanced sensitivity to cellular lipopolysaccharide challenge

Background: Inflammation has been associated with alcohol use disorder (AUD). A novel method to characterize AUD-related immune signaling involves probing Toll-like receptor (TLR)-4 stimulated monocyte production of intracellular cytokines (ICCs) via lipopolysaccharide (LPS). We evaluated relationships between AUD and ICC production at rest and after LPS stimulation.Methods: We analyzed blood samples from 36 participants (AUD N = 14; Controls N = 22), collected across time, with ICC expression assessed at rest (i.e., unstimulated) and following stimulation with LPS (i.e., a total of 5 repeated unstimulated or stimulated measures/participant). Markers assessed included tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), TNF-alpha and IL-6 co-expression, and interferon (IFN). For each marker, we constructed linear mixed models with AUD, LPS, and timepoint as fixed effects (BMI as covariate), allowing for random slope and intercept. AUD x LPS was included as an interaction.Results: For TLR4-stimulated monocyte production of TNF-alpha, there were effects of AUD (p < 0.01), LPS (p < 0.001), and AUD x LPS interaction (p < 0.05), indicating that individuals with AUD showed greater unstimulated- and stimulated monocyte expression of TNF-alpha. Similarly, for TLR4-stimulated monocyte co-expression of TNF-alpha and IL-6, there were effects of AUD (p < 0.01), LPS (p < 0.001), and AUD x LPS interaction (p < 0.05). No AUD or LPS effects were found for IL-6. Timepoint effects were observed on IL-6 and TNF-alpha/IL-6 co-expression (p < 0.001). Finally, for IFN there were also effects of AUD (p < 0.05), LPS (p < 0.001), and AUD x LPS (p < 0.001).Conclusions: Individuals with AUD showed greater resting or unstimulated levels of intracellular monocyte expression of TNF-alpha and IL-6/TNF-alpha co-expression than controls. AUD was associated with increases in TLR4-stimulated monocyte production of TNF-alpha and co-production of IL-6 and TNF-alpha. This is, to our knowledge, the first study to investigate relationships between AUD and monocyte production of proinflammatory cytokines, at rest and in response to TLR4 stimulation with LPS. The study extends previous findings on the roles of proinflammatory cytokines in AUD and serves as a critical proof of concept for the use of this method to probe neuroimmune mechanisms underlying AUD.