Poster Presentation Lorne Infection and Immunity 2022

Molecular basis underpinning the citrullinated self-antigen-mediated T cell immunity (#177)

Jia Jia Lim 1 , Claerwen M. Jones 1 , Tiing Jen Loh 1 , Yi Tian Ting 1 , Pirooz Zareie 1 , Khai L. Loh 1 , Nathan J. Felix 2 , Anish Suri 2 , Murray McKinnon 2 , Frederik Stevenaert 3 , Ravi K. Sharma 4 , Lars Klereskog 4 , Vivianne Malmstrom 4 , Daniel G. Baker 2 , Anthony W. Purcell 1 , Hugh H. Reid 1 , Nicole L. La Gruta 1 , Jamie Rossjohn 1 5 6
  1. Infection and Immunity Program & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia
  2. Janssen Research & Development, LLC, Horsham, Philadelphia, Pennsylvania, USA
  3. Janssen Research & Development, Turnhoutseweg 30, BE-2340, Beerse, Belgium
  4. Rheumatology Division, Department of Medicine, Karolinska Institute, Karolinska University Hospital 17177, Stockholm, Sweden
  5. Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, , Victoria 3800, Australia.
  6. Institute of Infection and Immunity, Cardiff University, School of Medicine, Heath Park, , Cardiff CF14 4XN, UK

T cell-mediated adaptive immune response is critical to discriminate the myriad of self-peptides from non-self-peptides presented by HLA molecule. Despite the key role of the HLA in protective immunity, HLA class II molecules are frequently correlated with aberrant T cell immunity, including autoimmunity and other immune-mediated inflammatory diseases. For example, HLA-DR4 allomorphs bearing the Shared Susceptibility Epitope (SE) are associated with increased susceptibility to rheumatoid arthritis (RA). The breaking of T cell tolerance can be attributed to several mechanisms, including unusual TCR-HLA docking topologies, altered peptide-binding to HLA molecules, molecular mimicry, and neoepitope generation. For example, certain post-translational modifications (PTM), such as the deamidation of glutamine, peptide trans-splicing, and citrullination, generate neo-epitopes with improved binding to a given HLA molecule. However, the interplay between the HLA molecule, post-translationally modified epitope and the responding T cell repertoire remain unclear.

To understand the molecular basis of the citrullinated self-epitope, HLA-DR4, and CD4 T cell, we synthesized citrullinated fibrinogen peptide, which is found abundantly in joint synovium of RA patient, and investigated structurally their impact on HLA-DR4 recognition. Using HLA-DR4 transgenic mice as a tool, we immunized the mice with single (Fibb-74cit69-81) and double citrullinated (Fibb-72,74cit69-81) fibrinogen b-peptide. Our result led to a population of HLA-DR4Fib b-74cit69-81 tetramer+ T cells that exhibited biased T cell receptor (TCR) b-chain usage, which was attributable to selective clonal expansion from the pre-immune repertoire. Crystal structures of pre- and post-immune TCRs showed that the SE of HLA-DR4 represented a main TCR contact zone. Immunisation with a double-citrullinated epitope (Fibb-72,74cit69-81) altered the responding HLA-DR4 tetramer+ T cell repertoire, which was due to the P2-citrulline residue interacting with the TCR itself. Together, our findings showed that citrullinated epitope revealed dual functionality, in both HLA-DR4 presentation and a direct TCR recognition determinant. In addition, analogous biased TCR b-chain usage towards the Fibb-74cit69-81 peptide was observed in healthy HLA-DR4+ individuals and HLA-DR4+ RA patients, thereby suggesting a link to human RA.

  1. J. J. Lim, C. M. Jones, T. J. Loh, Y. T. Ting, P. Zareie, K. L. Loh, N. J. Felix, A. Suri, M. McKinnon, F. Stevenaert, R. K. Sharma, L. Klareskog, V. Malmstr.m, D. G. Baker, A. W. Purcell, H. H. Reid, N. L. La Gruta, J. Rossjohn, The shared susceptibility epitope of HLA-DR4 binds citrullinated selfantigens and the TCR. Sci. Immunol. 6, eabe0896 (2021).