title: Human CD4+CD25+ regulatory T lymphocytes inhibit lipopolysaccharide-induced monocyte survival through a Fas/Fas ligand-dependent mechanism.
abstract: Although it is known that septic shock induces immunosuppression, the mechanism for this phenomenon is not well understood. Monocytes play a central role in septic shock pathophysiology, which is also characterized by an increased proportion of natural regulatory T (Treg) cells. We therefore investigated whether Treg could be involved in the decreased monocyte expression of CD14 and HLA-DR observed during septic shock. We demonstrated that human Treg inhibit LPS-induced retention of monocyte CD14. Because loss of CD14 is a hallmark of monocyte apoptosis, this suggests that Treg inhibit monocyte survival. This effect was largely mediated through the release of a soluble mediator that was not identical with either IL-10 or IL-4. The Fas/FasL pathway participated in the effect as it was blocked by anti-FasL Abs and reproduced by Fas agonist and recombinant soluble FasL. Furthermore, expression of FasL was much higher on Treg than on their CD25(-) counterparts. Collectively, these results indicate that Treg act on monocytes by inhibiting their LPS-induced survival through a proapoptotic mechanism involving the Fas/FasL pathway. This may be an important mechanism for septic shock-induced immunosuppression and may offer new perspectives for the treatment of this deadly disease.
authors.affiliation: Immunology Laboratory, Hôpital Neurologique, Hospices Civils de Lyon, 59 Boulevard Pinel, 69677 Lyon Cedex, France.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Venet
authors.forename: Alexandre
authors.initials: A
authors.lastname: Pachot
authors.forename: Anne-Lise
authors.initials: AL
authors.lastname: Debard
authors.forename: Julien
authors.initials: J
authors.lastname: Bohe
authors.forename: Jacques
authors.initials: J
authors.lastname: Bienvenu
authors.forename: Alain
authors.initials: A
authors.lastname: Lepape
authors.forename: William S
authors.initials: WS
authors.lastname: Powell
authors.forename: Guillaume
authors.initials: G
authors.lastname: Monneret
mesh_terms: D015704:CD4 Antigens / Q000032:analysis; D002470:Cell Survival / Q000276:immunology; D053222:Fas Ligand Protein / Q000276:immunology; D005260:Female; D006801:Humans; D007108:Immune Tolerance; D016753:Interleukin-10 / Q000378:metabolism; D053645:Interleukin-2 Receptor alpha Subunit / Q000032:analysis; D015847:Interleukin-4 / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000032:analysis; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*; D012772:Shock, Septic / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*
chemical_list: D015704:CD4 Antigens; D053222:Fas Ligand Protein; D053645:Interleukin-2 Receptor alpha Subunit; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016753:Interleukin-10; D015847:Interleukin-4