title: Ethanol inhibits lipid raft-mediated TCR signaling and IL-2 expression: potential mechanism of alcohol-induced immune suppression.
abstract: BACKGROUND
  Alcohol abuse has long-term deleterious effects on the immune system, and results in a depletion and loss of function of CD4(+) T lymphocytes, which regulate both innate and adaptive immunity. T-lymphocyte activation via T-cell receptor (TCR) involves the lipid raft colocalization and aggregation of proteins into the immunological signalosome, which triggers a signaling cascade resulting in the production of interleukin-2 (IL-2). IL-2 regulates the proliferation and clonal expansion of activated T cells and is essential for an effective immune response. The present work examines the mechanisms underlying ethanol-induced dysfunction of CD4(+) T lymphocytes based on the hypothesis that ethanol downregulates lipid raft-mediated TCR signal transduction and resultant IL-2 production.
  
  
  METHODS
  Primary or cultured human T lymphocytes were exposed to ethanol for 24 hours prior to stimulation with anti-CD3/anti-CD28 antibodies or phytohemagglutinin. Effects of ethanol exposure on TCR-signaling (including activation of Lck, ZAP70, LAT, and PLCγ1) and IL-2 gene expression were examined.
  
  
  RESULTS
  Exposure of both primary and cultured human CD4(+) T lymphocytes to physiologically relevant concentrations of ethanol leads to down-regulation of IL-2 mRNA and protein via inhibition of DNA-binding activity of NFAT, the essential transcription factor for IL-2. Ethanol decreases tyrosine phosphorylation and activation of upstream signaling proteins PLCγ1, LAT, ZAP70, and Lck. These effects are prevented by inhibition of metabolism of ethanol. Sucrose density gradient fractionation and confocal microscopy revealed that ethanol inhibited essential upstream lipid raft-mediated TCR-dependent signaling events, namely colocalization of Lck, ZAP70, LAT, and PLCγ1 with plasma membrane lipid rafts.
  
  
  CONCLUSIONS
  Overall, our data demonstrate that ethanol inhibits lipid raft-mediated TCR-signaling in CD4(+) T lymphocytes, resulting in suppression of IL-2 production. These findings may represent a novel mechanism underlying alcohol abuse-associated immune suppression and may be particularly relevant in diseases such as HIV/AIDS and hepatitis C virus infection where alcohol abuse is a known comorbidity.
authors.affiliation: Department of Medicine, University of Louisville Alcohol Research Center, University of Louisville, Louisville, KY 40202, USA.
authors.forename: Smita
authors.initials: S
authors.lastname: Ghare
authors.forename: Madhuvanti
authors.initials: M
authors.lastname: Patil
authors.forename: Prachi
authors.initials: P
authors.lastname: Hote
authors.forename: Jill
authors.initials: J
authors.lastname: Suttles
authors.forename: Craig
authors.initials: C
authors.lastname: McClain
authors.forename: Shirish
authors.initials: S
authors.lastname: Barve
authors.forename: Swati
authors.initials: S
authors.lastname: Joshi-Barve
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects; D002492:Central Nervous System Depressants / Q000009:adverse effects* / Q000276:immunology; D000431:Ethanol / Q000009:adverse effects* / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance / Q000187:drug effects*; D047468:Immunoprecipitation; D007376:Interleukin-2 / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011948:Receptors, Antigen, T-Cell / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000187:drug effects
chemical_list: D002492:Central Nervous System Depressants; D007376:Interleukin-2; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D000431:Ethanol