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α-enolase specific T cells in rheumatoid arthritis – a MHC class II tetramer approach
  1. Jennifer Pieper1,
  2. Mary Rieck2,
  3. Eddie James2,
  4. Charlotta Sandin1,
  5. Lars Klareskog1,
  6. Jane H. Buckner2,
  7. Vivianne Malmström1
  1. 1Karolinska Institutet, Rheumatology Unit, Stockholm, Sweden
  2. 2Benaroya Research Institute, Virginia Mason, Seattle, Washington, USA

Abstract

Backgroundand objectives Antibodies against citrullinated proteins are highly specific for rheumatoid arthritis (RA) and found in approximately 60% of patients and their presence is strongly associated with the human leucocyte antigen (HLA)-DRB1*0401 allele. α-enolase is one of these citrullinated antigens and antibodies against certain epitopes of this autoantigen are found in 40% of RA patients and are enriched in their synovial fluid. Here, the authors aimed to identify novel HLA-DRB1*0401 restricted T cell epitopes of α-enolase in order to construct and utilise major histocompatibility complex (MHC) class II tetramers to determine the frequency of cit-α-enolase-specific T cells in blood of DRB1*0401 RA patients.

Material and methods Overlapping peptides, both native and citrullinated versions, of full length α-enolase were analysed for 0401 binding via the Proimmune Class II Reveal assay and 13 citrullinated peptides came out as candidates. Following our own validation of HLA-DRB1*0401 binding, the authors constructed class II MHC tetramers loaded with either the native or citrullinated form of one of the peptides. Peripheral blood mononuclear cells (PBMCs) from HLA-DRB1*0401 RA patients were then screened for α-enolase specific T cells. T cells recognising the α-enolase peptide were identified using direct ex vivo analysis and additional analysis of the T cell phenotypes was performed by multi-colour flow cytometry. PBMCs from these patients were also expanded in vitro for 14 days with haemagglutinin (HA) or either the native or the citrullinated version of the α-enolase peptide and analysed on a FACS calibur.

Results In our binding assays the native and citrullinated form of our novel epitope bound to HLA-DRB1*0401 with a similar affinity. Tetramers were constructed and allowed for the detection of α-enolase specific T cells in the blood of DRB1*0401 RA patients. The frequency varied and was markedly lower than that of HA-specific T cells in the same individuals. When comparing the phenotype, our preliminary results suggest that T cells specific for the native α-enolase peptide are predominantly of a naïve phenotype, whereas the T cells specific for the citrullinated version are of a memory phenotype.

Conclusions The authors have identified a novel α-enolase T cell epitope that binds HLA-DRB1*0401 in both its native and citrullinated form. Interestingly it appears that the cit-specific T cells are antigen-experienced and have previously been activated in the patients, while the native-specific T cells appeared naïve. In the future the authors plan to further enumerate and characterise cit-α-enolase specific T cells in RA and controls and to extend these studies to synovial fluid.

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