EXTENDED REPORT

Analysis of the CD8+ T cell response to the G1 domain of aggrecan in ankylosing spondylitis

J Zou¹, H Appel¹, M Rudwaleit¹, A Thiel², J Sieper^1,2

¹ Department of Gastroenterology and Rheumatology, Charité Berlin, Campus Benjamin Franklin, Berlin, Germany
² German Rheumatology Research Centre, Berlin, Germany

Correspondence to:
Dr J Sieper
Department of Gastroenterology and Rheumatology, Charité Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany; joachim.sieper{at}charite.de

Background: CD4+ T cell responses to the G1 domain of aggrecan in patients with ankylosing spondylitis (AS) were recently reported. Whether such an immune response can be seen in the CD8+ subpopulation has not yet been determined.

Objective: To determine if HLA-B27 restricted G1-specific CD8+ T cells are present in AS and to analyse immunodominant CD8+ T cell epitopes.

Methods: Peripheral blood mononuclear cells of 45 patients with AS were stimulated with overlapping 18-mer peptides covering the whole G1 protein. Results were compared with those for patients with rheumatoid arthritis (RA) and healthy controls. For epitope analysis, G1-specific interferon gamma positive (IFN+) T cells were isolated by magnetic activated cell sorting. After in vitro expansion, CD8+ T cells were restimulated with 14 subpools of G1 peptides. T cells responding to G1 peptide subpools were quantified by flow cytometry according to IFN secretion. Predicted peptides were subsequently confirmed by stimulation with single peptides.

Results: G1-specific CD8+ T cell responses were found in 29/45 (64%) patients with AS, 18/35 (51%) patients with RA, but not in healthy controls. Five CD8+ T cell epitopes were identified as immunodominant in five patients. However, the T cell response was not HLA-B27 restricted. Nonamer peptides with an HLA-B27 binding motif did not induce a T cell response.

Conclusion: A G1 peptide-specific CD8+ T cell response is present in AS but also in patients with RA. It does not seem to be HLA-B27 restricted. Whether such a response has a role in the pathogenesis of AS needs clarification.

Abbreviations: AA, amino acid; AS, ankylosing spondylitis; IFN, interferon ; IL, interleukin; MACS, magnetic activated cell sorting; PB, peripheral blood; PBMCs, peripheral blood mononuclear cells; RA, rheumatoid arthritis; SEB, Staphylococcus enterotoxin B; TNF, tumour necrosis factor

Keywords: CD8+ T cells; aggrecan; ankylosing spondylitis; self antigens

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