title: Human fetal retinal pigment epithelial cells induce apoptosis in allogenic T-cells in a Fas ligand and PGE2 independent pathway.
abstract: OBJECTIVE
  To evaluate the inhibitory effect of human fetal retinal pigment epithelium (HFRPE) on the activation of human T-cells.
  
  
  METHODS
  Pure cultures of HFRPE cells were incubated with purified human T-cells in three different activation assays: 1) allogenic peripheral blood mononuclear cells; 2) OKT3 coated beads in the presence of accessory cells; and 3) stimulation with phorbol ester and phytohemagglutinin.
  
  
  RESULTS
  HFRPE cells suppressed the activation of T-cells in all three assays. The mechanism of HFRPE mediated T-cell suppression was apoptosis. The role of Fas ligand(FasL)/Fas-mediated T-cell suppression was excluded, since FasL protein or mRNA could not be detected on HFRPE cells with flow cytometry and by reverse transcriptase polymerase chain reaction, respectively. Additionally, the inhibitory effect of HFRPE cells could not be blocked by anti-Fas ligand or antagonistic anti-Fas antibodies. Moreover, HFRPE cells suppressed the proliferation of anti-CD3 mAb mediated T-cell proliferation of murine splenocytes isolated from lpr mice. The inhibitory effect of HFRPE cells was not PGE2 mediated, since indomethacin could not restore the T-cell activation. Although the HFRPE mediated T-cell apoptosis was cell-cell contact independent, it was not induced by secretion of TNF-alpha, TGF-beta, or IL-10. The ratio between HFRPE and T-cells had a major impact on the HFRPE's inhibitory effect.
  
  
  CONCLUSIONS
  HFRPE cells suppressed the activation of human T-cells by induction of T-cell apoptosis through a process that involves the secretion of soluble factors. The HFRPE mediated T-cell suppression was dependent on the ratio between HFRPE and T-cells. This undefined pathway of T-cell apoptosis may play a role in the maintenance of immune privilege in the subretinal space and may reduce the severity of the immune response after HFRPE transplantation.
authors.affiliation: Department of Ophthalmology and Visual Science, University of Chicago, Illinois 60637, USA. krezaei@midway.uchicago.edu
authors.forename: K A
authors.initials: KA
authors.lastname: Rezai
authors.forename: R T
authors.initials: RT
authors.lastname: Semnani
authors.forename: L
authors.initials: L
authors.lastname: Farrokh-Siar
authors.forename: K J
authors.initials: KJ
authors.lastname: Hamann
authors.forename: S C
authors.initials: SC
authors.lastname: Patel
authors.forename: J T
authors.initials: JT
authors.lastname: Ernest
authors.forename: G A
authors.initials: GA
authors.lastname: van Seventer
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002450:Cell Communication / Q000502:physiology; D003287:Contrast Media; D016207:Cytokines / Q000502:physiology; D015232:Dinoprostone / Q000502:physiology*; D053222:Fas Ligand Protein; D005333:Fetus / Q000166:cytology / Q000502:physiology*; D019793:Fluorescein; D006801:Humans; D008213:Lymphocyte Activation / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D010857:Pigment Epithelium of Eye / Q000196:embryology*; D013601:T-Lymphocytes / Q000502:physiology*
chemical_list: D003287:Contrast Media; D016207:Cytokines; C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D015232:Dinoprostone; D019793:Fluorescein