title: Silencing or inhibition of endoplasmic reticulum aminopeptidase 1 (ERAP1) suppresses free heavy chain expression and Th17 responses in ankylosing spondylitis.
abstract: OBJECTIVE
  Human leucocyte antigen (HLA)-B27 and endoplasmic reticulum aminopeptidase 1 (ERAP1) are strongly associated with ankylosing spondylitis (AS). ERAP1 is a key aminopeptidase in HLA class I presentation and can potentially alter surface expression of HLA-B27 free heavy chains (FHCs). We studied the effects of ERAP1 silencing/inhibition/variations on HLA-B27 FHC expression and Th17 responses in AS.
  
  
  METHODS
  Flow cytometry was used to measure surface expression of HLA class I in peripheral blood mononuclear cells (PBMCs) from patients with AS carrying different ERAP1 genotypes (rs2287987, rs30187 and rs27044) and in ERAP1-silenced/inhibited/mutated HLA-B27-expressing antigen presenting cells (APCs). ERAP1-silenced/inhibited APCs were cocultured with KIR3DL2CD3ε-reporter cells or AS CD4+ T cells. Th17 responses of AS CD4+ T cells were measured by interleukin (IL)-17A ELISA and Th17 intracellular cytokine staining. FHC cell surface expression and Th17 responses were also measured in AS PBMCs following ERAP1 inhibition.
  
  
  RESULTS
  The AS-protective ERAP1 variants, K528R and Q730E, were associated with reduced surface FHC expression by monocytes from patients with AS and HLA-B27-expressing APCs. ERAP1 silencing or inhibition in APCs downregulated HLA-B27 FHC surface expression, reduced IL-2 production by KIR3DL2CD3ε-reporter cells and suppressed the Th17 expansion and IL-17A secretion by AS CD4+ T cells. ERAP1 inhibition of AS PBMCs reduced HLA class I FHC surface expression by monocytes and B cells, and suppressed Th17 expansion.
  
  
  CONCLUSIONS
  ERAP1 activity determines surface expression of HLA-B27 FHCs and potentially promotes Th17 responses in AS through binding of HLA-B27 FHCs to KIR3DL2. Our data suggest that ERAP1 inhibition has potential for AS treatment.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Liye
authors.initials: L
authors.lastname: Chen
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Ridley
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Ariane
authors.initials: A
authors.lastname: Hammitzsch
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Mohammad Hussein
authors.initials: MH
authors.lastname: Al-Mossawi
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Bunting
authors.affiliation: Department of Chemistry, University of Athens, Athens, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Georgiadis
authors.affiliation: Department of Rheumatology, Royal Berkshire Hospital, Reading, UK.
authors.forename: Antoni
authors.initials: A
authors.lastname: Chan
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Kollnberger
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Bowness
mesh_terms: D000328:Adult; D000626:Aminopeptidases / Q000037:antagonists & inhibitors* / Q000235:genetics; D000938:Antigen-Presenting Cells / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018920:Coculture Techniques; D005260:Female; D020868:Gene Silencing; D005838:Genotype; D015796:HLA-B27 Antigen / Q000378:metabolism; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000378:metabolism*; D007376:Interleukin-2 / Q000096:biosynthesis; D008297:Male; D008875:Middle Aged; D015778:Minor Histocompatibility Antigens; D009000:Monocytes / Q000276:immunology; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000276:immunology*; D058504:Th17 Cells / Q000276:immunology*
chemical_list: D015796:HLA-B27 Antigen; D007143:Immunoglobulin Heavy Chains; D007376:Interleukin-2; D015778:Minor Histocompatibility Antigens; D000626:Aminopeptidases; C464841:ERAP1 protein, human
keywords: Ankylosing Spondylitis; Autoimmunity; T Cells