title: Myeloid suppressor cells induced by retinal pigment epithelial cells inhibit autoreactive T-cell responses that lead to experimental autoimmune uveitis.
abstract: OBJECTIVE
  To test whether retinal pigment epithelial (RPE) cells are able to induce myeloid-derived suppressor cell (MDSC) differentiation from bone marrow (BM) progenitors.
  
  
  METHODS
  BM cells were cocultured with or without RPE cells in the presence of GM-CSF and IL-4. Numbers of resultant MDSCs were assessed by flow cytometry after 6 days of incubation. The ability of the RPE cell-induced MDSCs to inhibit T cells was evaluated by a CFSE-based T-cell proliferation assay. To explore the mechanism by which RPE cells induce MDSC differentiation, PD-L1-deficient RPE cells and blocking antibodies against TGF-β, CTLA-2α, and IL-6 were used. RPE cell-induced MDSCs were adoptively transferred into mice immunized with interphotoreceptor retinoid-binding protein in complete Freund's adjuvant to test their efficacy in suppressing autoreactive T-cell responses in experimental autoimmune uveitis (EAU).
  
  
  RESULTS
  RPE cells induced the differentiation of MDSCs. These RPE cell-induced MDSCs significantly inhibited T-cell proliferation in a dose-dependent manner. PD-L1-deficient RPE cells induced MDSC differentiation as efficiently as wild-type RPE cells, and neutralizing TGF-β or CTLA-2α did not alter the numbers of induced MDSCs. However, blocking IL-6 reduced the efficacy of RPE cell-induced MDSC differentiation. Finally, adoptive transfer of RPE cell-induced MDSCs suppressed IRBP-specific T-cell responses that led to EAU.
  
  
  CONCLUSIONS
  RPE cells induce the differentiation of MDSCs from bone marrow progenitors. Both cell surface molecules and soluble factors are important in inducing MDSC differentiation. PD-L1, TGF-β, and CTLA-2α were not measurably involved in RPE cell-induced MDSC differentiation, whereas IL-6 was important in the process. The induction of MDSCs could be another mechanism by which RPE cells control immune reactions in the retina, and RPE cell-induced MDSCs should be further investigated as a potential approach to therapy for autoimmune posterior uveitis.
authors.affiliation: Department of Pathology, Case Western Reserve University School of Medicine, 2085 Adelbert Road, Cleveland, OH 44106, USA.
authors.forename: Zhidan
authors.initials: Z
authors.lastname: Tu
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Dawn
authors.initials: D
authors.lastname: Smith
authors.forename: Catherine
authors.initials: C
authors.lastname: Doller
authors.forename: Sunao
authors.initials: S
authors.lastname: Sugita
authors.forename: Chi-Chao
authors.initials: CC
authors.lastname: Chan
authors.forename: Shiguang
authors.initials: S
authors.lastname: Qian
authors.forename: John
authors.initials: J
authors.lastname: Fung
authors.forename: Rachel R
authors.initials: RR
authors.lastname: Caspi
authors.forename: Lina
authors.initials: L
authors.lastname: Lu
authors.forename: Feng
authors.initials: F
authors.lastname: Lin
mesh_terms: D000818:Animals; D001327:Autoimmune Diseases / Q000276:immunology* / Q000473:pathology; D015551:Autoimmunity; D002454:Cell Differentiation; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005434:Flow Cytometry; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D055213:Retinal Pigment Epithelium / Q000276:immunology* / Q000473:pathology; D013601:T-Lymphocytes / Q000276:immunology*; D014605:Uveitis / Q000276:immunology* / Q000473:pathology