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Endoplasmic reticulum aminopeptidase 1 (ERAP1) exhibits functionally significant interaction with HLA-B27 and relates to subtype specificity in ankylosing spondylitis
  1. Nigil Haroon1,2,
  2. Florence W Tsui2,
  3. Barbara Uchanska-Ziegler3,
  4. Andreas Ziegler3,
  5. Robert D Inman1,2
  1. 1Division of Rheumatology, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada
  2. 2Genetics and Development Department, Toronto Western Research Institute and University of Toronto, Toronto, Ontario, Canada
  3. 3Institut für Immungenetik, Charité-Universitätsmedizin Berlin, Freie Universität Berlin, Berlin, Germany
  1. Correspondence to Dr RD Inman, Rheumatology Department, Toronto Western Hospital, 399 Bathurst Street, Toronto, ON, Canada M5T2S8; robert.inman{at}


Objectives The functional interaction of endoplasmic reticulum aminopeptidase 1 (ERAP1) with human leucocyte antigen (HLA)-B*27 could be important in the pathogenesis of ankylosing spondylitis (AS). AS is associated with B*27:04 and B*27:05, but not with B*27:06 and B*27:09. The authors studied the surface expression of peptide-HLA(pHLA)-B27 complexes and HLA class-I free heavy chains (FHCs) on peripheral blood mononuclear cells of patients with AS with different ERAP1 single nucleotide polymorphisms. The effects of ERAP1 suppression on HLA-B*27 subtypes were tested.

Methods Peripheral blood mononuclear cells were collected from Caucasian patients with AS for flow cytometry and were stained for pHLA and FHCs. Genotyping was performed for two ERAP1 single nucleotide polymorphisms (rs27044(C/G) and rs30187(C/T)). C1R cells transfected with different HLA-B27 subtypes (B*27:04, B*27:05, B*27:06 and B*27:09) were subjected to ERAP1 suppression by small interfering RNA and stained using the monoclonal antibody (mAb) MARB4 as well as antibodies for pHLA, FHC, intracellular FHC (IC-FHC). MARB4 has been reported to bind to HLA-B27 with extended peptides.

Results The authors found variations in FHC expression on the monocytes of patients with AS, depending on different ERAP1 variants. Subsequently, using Hmy2.C1R cells in vitro, the authors show that ERAP1 suppression leads to increased IC-FHC and surface pHLA that react with the monoclonal antibody MARB4. The functional interaction between ERAP1 and HLA-B27 molecules appears to be subtype-specific, since ERAP1 suppression leads to changes only in cells expressing B*27:04 or B*27:05, but not B*27:06 or B*27:09.

Conclusions Direct or indirect alterations in the ERAP1-HLA-B27 interaction could be crucial by causing changes in peptide presentation or FHC formation by HLA-B27 molecules, as well as by contributing to differential subtype association in spondyloarthropathies.

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  • Funding Funding was provided by the Canadian Institutes of Health Research.

  • Competing interests None.

  • Ethics approval Ethics approval was obtained from the University Health Network Research Ethics Board.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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