title: PD-L1 partially protects renal tubular epithelial cells from the attack of CD8+ cytotoxic T cells.
abstract: BACKGROUND
  Activated infiltrating T cells play a crucial role in nephritic inflammation via the direct interaction with proximal tubular epithelial cells (TEC). Under inflammatory conditions, major histocompatibility complex class I and II molecules are upregulated on the surface of renal TEC, enabling them to function as "non-professional" antigen-presenting cells (APC) to activate T cells, and, in turn to be targeted by cytotoxic T lymphocytes (CTL) to cause tissue damage. It is known that co-stimulatory (e.g. B7/CD28) and co-inhibitory (e.g. PD-L1/PD-1) signals regulate and determine the magnitude of T cell responses. In this study, we examined the expression of co-stimulatory molecule PD-L1 by renal TEC and the functional role of renal PD-L1/PD-1 pathway in regulating CD8+ T cell responses induced by antigen-presenting renal TEC.
  
  
  METHODS
  Renal TEC were treated with type I and type II interferons (IFN-alpha, IFN-beta or IFN-gamma). PD-L1 expression was then determined with flow cytometry and RT-PCR. To investigate the functional role of renal epithelial PD-L1 on CD8+ CTL responses, H-2K(b)-restricted, OVA(257-264) peptide-specific CD8+ T cells isolated from OT-1 T cell receptor transgenic mice were co-incubated with IFN-stimulated, OVA(257-264) peptide-pulsed congeneic TEC. The activation of OT-1 CD8+ CTL was estimated either by IFN-gamma production in the supernatants of co-cultures or by CTL activity.
  
  
  RESULTS
  TECs do not constitutively express PD-L1 on their surface. However, a strong and dose-dependent upregulation of PD-L1 was observed on TEC after stimulation with IFN-beta or IFN-gamma, but not with IFN-alpha. OVA(257-264) peptide pulsed-TEC were able to activate OT-1 CD8+ T cells, indicated by the high amount of IFN-gamma production and cytolysis of TEC. Blockade of epithelial PD-L1 with specific mAb significantly increased OT-1 CD8+ T cell activity, indicating that the PD-L1 pathway has a negative effect on CD8+ T cell responses. Moreover, IFN- beta- or IFN-gamma-stimulated TEC with high surface PD-L1 expression were more resistant to the cytolysis by OT-1 CTL.
  
  
  CONCLUSIONS
  Together our data reveal that the renal PD-L1/PD-1 pathway has a negative effect on CD8+ CTL activation. PD-L1 might, therefore, act as a protective molecule on TEC, downregulating the cytotoxic renal parenchymal immune response.
authors.affiliation: Institute of Physiology, University of Zurich-Irchel, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland. ying.waeckerle-men@access.unizh.ch
authors.forename: Ying
authors.initials: Y
authors.lastname: Waeckerle-Men
authors.forename: Astrid
authors.initials: A
authors.lastname: Starke
authors.forename: Rudolf P
authors.initials: RP
authors.lastname: Wüthrich
mesh_terms: D000818:Animals; D018122:B7-1 Antigen / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D060890:B7-H1 Antigen; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D015536:Down-Regulation / Q000276:immunology; D004847:Epithelial Cells / Q000276:immunology* / Q000473:pathology; D016899:Interferon-beta / Q000502:physiology; D007371:Interferon-gamma / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000276:immunology* / Q000473:pathology; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010455:Peptides / Q000235:genetics / Q000502:physiology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D015854:Up-Regulation / Q000276:immunology
chemical_list: D018122:B7-1 Antigen; D060890:B7-H1 Antigen; C498919:Cd274 protein, mouse; D008562:Membrane Glycoproteins; D010455:Peptides; D016899:Interferon-beta; D007371:Interferon-gamma