title: Human fetal retinal pigment epithelium suppresses the activation of CD4(+) and CD8(+) T-cells.
abstract: BACKGROUND
  The suppressive effect of human fetal retinal pigment epithelium (HFRPE) on the activation of human CD4(+) and CD8(+) T-cells was evaluated in vitro.
  
  
  METHODS
  Pure populations of CD4(+) and CD8(+) T-cells were isolated from human peripheral blood-derived buffy coats by negative immunomagnetic selection. The purity of the cells was examined by flow cytometry using anti-CD3-FITC, anti-CD4-FITC, anti-CD8-PE, and anti-CD20-PE mAbs. HFRPE cells were isolated from fetal eyes and pure cultures were obtained. The effect of normal or IFN-gamma-activated HFRPE cells at early (P3) or late (P6) passages on the activation of CD4(+) and CD8(+) T-cells was assessed in two different T-cell activation assays. In both activation models anti-CD3 mAb (OKT3) provided the antigen-specific signal. The secondary signal for the activation of CD4(+) and CD8(+) T-cells was provided with anti-CD18 mAb (TS1/18) and anti-CD28 mAb (9.3) in the first and the second assay respectively. Cross-linking of these soluble mAbs was performed with sheep-anti-mouse IgG-coated latex beads. The T-cell activation was determined by cell proliferation measured by [(3)H]thymidine incorporation. In each activation assay T-cells were incubated with HFRPE cells in a ratio of T-cells to HFRPE of 1:1 or 1:4.
  
  
  RESULTS
  CD4(+) and CD8(+) T-cells were activated by cross-linking CD3 and CD18 in the first assay (CD3/CD18) and CD3 and CD28 in the second assay (CD3/CD28). In both assays HFRPE inhibited the activation of CD4(+) and CD8(+) T-cells. IFN-gamma-activated HFRPE cells totally suppressed the T-cell activation at a 1:1 ratio. This suppressive effect was weaker at lower cell ratios. Some donor variation was observed in the inhibition at the lower cell ratios, especially for the inhibition of CD8(+) T-cell activation with anti-CD3/CD18. The passaging of HFRPE cells did not alter their suppressive effect on CD4(+) and CD8(+) T-cells.
  
  
  CONCLUSIONS
  HFRPE cells suppressed the activation of both CD4(+) and CD8(+) T-cells in vitro. These findings suggest that RPE-induced immune suppression may play a significant role in maintaining immune privilege in the subretinal space.
authors.affiliation: Department of Ophthalmology and Visual Science, University of Chicago, 939 East 57th Street, Chicago, IL 60637, USA.
authors.forename: L
authors.initials: L
authors.lastname: Farrokh-Siar
authors.forename: K A
authors.initials: KA
authors.lastname: Rezai
authors.forename: R T
authors.initials: RT
authors.lastname: Semnani
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: D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D015703:Antigens, CD / Q000276:immunology; D016516:CD4-CD8 Ratio; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D002455:Cell Division; D002478:Cells, Cultured; D005260:Female; D005333:Fetus / Q000166:cytology / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D007165:Immunosuppression Therapy; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D016853:Muromonab-CD3 / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000276:immunology*; D011247:Pregnancy
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D007166:Immunosuppressive Agents; D016853:Muromonab-CD3