Many of the differentially expressed genes found in the human and mouse studies are part of the TLR signaling pathway. In fact, ethanol-mediated increases in glial activation, inflammatory mediators, and apoptosis are prevented in microglia lacking TLR4 and in microglia from TLR4-deficient mice [30*,31]. Ethanol activation of NF-κB in brain microglia is dependent on TLR4 [30*,31] and roles for TLR4 accessory proteins, MD2 and CD14, have been demonstrated following alcohol exposure in TLR4-deficient cells [30*]. Blockade of TLR4 receptors prevented ethanol-induced inflammatory signaling in astrocytes, including prevention of NF-κB activation and cell death [32]. Also, brain protein expression of TLR2, TLR3, and TLR4 increased in post-mortem alcoholic brain and in mouse brain following ethanol treatment [19]. The association between TLRs and alcohol has even been reported in Drosophila, where an upregulation of genes in toll and immune deficiency pathways was produced by alcohol exposure [33]. Thus, there is substantial support for alcohol action on innate immune genes and specific evidence for an overlap of TLR signaling by alcohol among different species.
