Lymphoblastoid cells express HLA-B27 homodimers both intracellularly and at the cell surface following endosomal recycling

Authors

  • Lucy A. Bird,

    Corresponding author
    1. MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, GB
    • MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, OX3 9DS, GB Fax: +44-1865-222502
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    • The first two authors contributed equally to this work.

  • Chen Au Peh,

    1. MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, GB
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  • Simon Kollnberger,

    1. MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, GB
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  • Tim Elliott,

    1. Cancer Sciences Division, University of Southampton School of Medicine, Southampton General Hospital, Southampton, GB
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  • Andrew J. McMichael,

    1. MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, GB
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  • Paul Bowness

    1. MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, GB
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Abstract

The MHC class I allele HLA-B27 is very strongly associated with development of autoimmune spondyloarthritis, although the disease mechanism remains unknown. Class I molecules classically associate in the endoplasmic reticulum (ER) with β2-microglobulin (β2m) and antigenic peptides for cell surface expression and presentation to T cells. We have previously shown that HLA-B27 is capable of forming β2m-free disulfide-bonded homodimers in vitro. Here we show that HLA-B27 forms disulfide-bonded homodimers in vivo by two distinct pathways. HLA-B27 homodimers form in the ER but appear unable to egress to the cell surface in human cells. Cell surface HLA-B27 homodimers are abundantly expressed in a variety of lymphoid cell lines. Experiments with inhibitors indicate that HLA-B27 homodimers can arise from cell-surface heterodimers via an endosome-dependent recycling pathway. HLA-B27 homodimer expression on the cell surface of 721.220 is dependent on the unpaired cysteine67 and is inhibited by restoration of tapasin function or by incubation with peptides that bind strongly to HLA-B27 heterodimers. Cell surface expressed HLA-B27 homodimers are likely to be immunologically reactive ligands for NK family immunoreceptors and, hence, could play a pathogenic role in spondyloarthritis.

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