Oral Presentation HUPO 2019 - 18th Human Proteome Organization World Congress

HLA-B27 immunopeptidome: Understanding the connection between Salmonella typhimurium infection and ankylosing spondylitis (#27)

Terry C.C Lim Kam Sian 1 , Pouya Faridi 1 , Ralf B Schittenhelm 1 2 , Anthony W Purcell 1
  1. Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
  2. Monash Biomedical Proteomics Facility, Monash Biomedicine Discovery Institute, Monash University, Clayton, Australia

The association of the Human Leukocyte Antigen (HLA) B27 with ankylosing spondylitis (AS) is one of the strongest associations that has ever been described between an autoimmune disease and a HLA allele. One of the leading hypotheses is the arthritogenic peptide theory, which assumes that molecular mimicry between a foreign- and a self-peptide leads to breakdown of the immune tolerance and ensuing autoimmunity. A major support for this theory comes from the observation that patients often develop AS following gastrointestinal bacterial infection. To identify putative arthritogenic peptides, we analysed both the linear and spliced HLA-B27 immunopeptidome before and after infection with Salmonella typhimurium, which represents one of the bacterial strains associated with AS.

Methods: A combination of high-resolution mass spectrometry, de novo sequencing and cutting-edge bioinformatics was used to identify the linear and spliced peptides presented on the 8 most common HLA-B27 allotypes (HLA-B*27:02-HLA-B*27:09) before and after infection with S.typhimurium.

Results: We identified ~13500 unique HLA-B27 peptides of which ~4500 have never been reported previously. A careful comparison of these peptides showed that bacterial infection did not impact on the HLA-B27 immunopeptidome with regards to the peptide length preference or the consensus binding motif. A comparative analysis against bacteria that have been reported to be associated with AS, revealed 460 novel putative arthritogenic peptides. Interestingly, <1% of the linear peptides identified were Salmonella-derived. In contrast, Salmonella spliced peptides represented a higher proportion of the immunopeptidome of ~4% (ratio of cis:trans of 4:1) and were derived from a different subset of source proteins than the linear peptides.

Conclusion: We describe 460 novel putative arthritogenic peptides and further show that spliced peptides can increase the breath of the immunopeptidome. However, further analyses such as peptide binding studies, immunological assays and structural investigations are required to confirm immunogenicity and to validate these peptides.