title: Studies on naïve CD4+CD25+T cells inhibition of naïve CD4+CD25- T cells in mixed lymphocyte cultures.
abstract: BACKGROUND
  Naïve CD4+CD25+T cells suppress immune responses in a non-antigen specific manner. The effects of naïve CD4+CD25+T cells in suppressing alloimmune responses as assayed in the mixed lymphocyte culture (MLC) is poorly understood.
  
  
  METHODS
  The alloreactivity of naïve CD4+CD25+, CD4+CD25(-) and unfractionated CD4+T cells from DA rats was compared in MLC with MHC incompatible stimulator cells. The response of Lewis and PVG cells to semi-allogeneic (LewisxPVG)F1 cells and fully allogeneic stimulators were compared. Potential mechanisms of suppression were examined by blocking T cell cytokines, produced by activated CD4+CD25+T cells.
  
  
  RESULTS
  Proliferation of CD4+CD25(-)T cells was significantly greater than unfractionated CD4+T cells to both allogeneic and syngeneic stimulator cells. CD4+CD25+T cells had no response to syngeneic stimulators and very low proliferative responses to alloantigen due to the Foxp3(-) cells. Admixing CD4+CD25+T cells with CD4+CD25(-)T cells at a ratio of 1:10 reduced the proliferation to that of unfractionated CD4+ T cells. At a ratio of 1:1 proliferation was nearly totally suppressed, IL-2, IL-4 and IL-5 mRNA induction was reduced but IFN-gamma, IL-10, TGF-beta and inducible nitric oxide (iNOS) mRNA induction was spared. The inhibition by CD4+CD25+ T cells was not due to their consumption of IL-2 nor to anti-CD25mAb that had been used to enrich the cells being releases and blocking the IL-2 receptor on CD4+CD25(-)T cells that had been activated by alloantigen and induced to express CD25. Blocking IFN-gamma, IL-10, TGF-beta, IL-5 or iNOS did not prevent CD4+CD25+T cell's inhibition of CD4+CD25(-)T cell proliferation. Blocking IFN-gamma or iNOS enhanced CD4+CD25(-)T cell proliferation only in the absence of CD4+CD25+T cells. Depletion of CD4+CD25+T cells enhanced responses to syngeneic stimulator cells, but this anti-self suppression did not regulate the response to alloantigen on semi-allogeneic stimulators.
  
  
  CONCLUSIONS
  Two independent mechanisms that control proliferation of CD4+CD25(-)T cells in MLC were identified that naive CD4+CD25+T cells mediated by cell to cell contact and not release of cytokines produced in the cultures, and that CD4+CD25(-)T cells producing IFN-gamma to induce iNOS.
authors.affiliation: Immune Tolerance Group, Department of Medicine, University of N.S.W., Sydney, NSW, Australia. b.hall@unsw.edu.au
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Hall
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Robinson
authors.forename: Karren M
authors.initials: KM
authors.lastname: Plain
authors.forename: Nirupama D
authors.initials: ND
authors.lastname: Verma
authors.forename: Nicole
authors.initials: N
authors.lastname: Carter
authors.forename: Rochelle A
authors.initials: RA
authors.lastname: Boyd
authors.forename: Giang T
authors.initials: GT
authors.lastname: Tran
authors.forename: Suzanne J
authors.initials: SJ
authors.lastname: Hodgkinson
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000276:immunology; D049109:Cell Proliferation; D002469:Cell Separation; D018920:Coculture Techniques; D007108:Immune Tolerance / Q000276:immunology*; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism*; D007959:Lymphocyte Culture Test, Mixed; D051381:Rats; D011917:Rats, Inbred Lew; D016176:T-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000378:metabolism
chemical_list: D053645:Interleukin-2 Receptor alpha Subunit