The mechanisms of alcohol-mediated T-cell death and mechanisms of priming and LPS signaling in macrophages

Clinical and experimental studies have shown that an important harmful consequence of excessive alcohol consumption is immunosuppression; specifically, a deleterious effect on the innate and the adaptive immune response. Alcohol depletes the mature T-cell population, a critical component of the adaptive immune response. Although it is well documented that alcohol intake can cause depletion of T-cells, the mechanism of how alcohol mediates its effects is unclear. Mechanisms of T-cell depletion of pathological significance include Activation Induced Cell Death (AICD) and Fas mediated apoptosis. In the present study, we investigate the effect of alcohol on AICD and Fas mediated apoptosis in T-cells. We demonstrate that alcohol pretreatment enhances AICD in Jurkat cells, and peripheral blood lymphocytes, and Fas mediated apoptosis in Jurkat cells. Furthermore, we find that the alcohol-mediated enhancement of AICD and Fas mediated apoptosis involves increased activation of caspase-3. Excessive alcohol consumption causes a dysregulation in circulating levels of cytokines, molecular mediators that are the cornerstone of the innate response. Priming of LPS signaling in monocytes/macrophages is an important mechanism of the cytokine imbalance that is associated with chronic alcohol consumption. While it has emerged that priming of Lipopolysaccharide (LPS) signaling in monocytes/macrophages is involved in alcohol toxicity, the mechanistic details associated with priming and LPS signaling are unclear. In the present study, Interferon gamma (IFNγ) primed and LPS stimulated RAW 264.7 macrophages show enhanced Akt kinase and IRAK1 kinase activity. The cells also show enhanced NFκB DNA binding and transcriptional activation, IL-6 cytokine expression, and this priming event is nitric oxide independent. A higher dose of IFNγ increases LPS stimulated IL-10 production while simultaneously suppressing LPS dependant TNFα production in RAW 264.7 cells. Genetic analyses and the use of a pharmacological inhibitor suggest that Akt kinase can acts as a negative regulator of LPS inducible NFκB activation. Taken together this data provides mechanisms for alcohol mediated T-cell depletion, and greater insight into the complexities of LPS signaling, and IFNγ mediated priming of LPS signaling, in macrophages.