Antigen Specific CD4+ T cells and their role in viral infection and autoimmune disease

Abstract

INTRODUCTION: Rheumatoid arthritis (RA) is an inflammatory disease where the immune system targets the joints, eventually leading to their destruction if untreated. RA is characterised by the presence of anti-citrullinated protein antibodies (ACPA) in the peripheral blood of patients. Previous studies have also identified a population of CD4+ T cells that can recognise and bind to citrullinated cartilage antigens presented by the HLA-DRβ1*04:01 molecule, carriage of which is itself recognised as a susceptibility factor for RA. The immunophenotype of antigen-specific CD4+ T cells in ACPA+ (seropositive) RA is underexplored. CD4+ T peripheral helper (Tph) and HLA-DR+CD27- T effector memory cells represent newly identified T helper (Th) cell subset allegedly playing a central role in the aetiology of seropositive RA. AIMS: The involvement of CD4+ T cells specific for citrullinated antigens in RA via manifestation of an activated HLA-DR+CD27- or pro-inflammatory PD-1highCXCR5- was investigated. Next, their phenotype was compared with that of CD4+ T cells specific for viral peptides and clonally expanded synovial CD4+ T cells. METHODS: Peripheral blood mononuclear cells (PBMCs) from 15 patients and 7 healthy controls carrying at least one HLA-DRB1*04:01 gene were tested with MHC class II tetramers loaded with viral peptides and citrullinated autoantigens and immunophenotyped for the markers CD45RO, CCR7, HLA-DR, CD27, PD-1 and CXCR5. PBMCs and synovial fluid cells from 23 patients diagnosed with inflammatory arthritis (including RA) and 3 patients with non-inflammatory arthritis were immunophenotyped for the same immune markers and their T cell receptor Vbeta type. RESULTS: RA patients were found on average to have higher number of circulating CD4+ T cells specific for citrullinated antigens compared to healthy volunteers. Antigen-specific CD4+ T cells did not demonstrate an HLA-DR+CD27- or PD-1highCXCR5- phenotype, however showed a higher proportion of the HLA-DR+CD27+ phenotype compared to the total CD4+ population in peripheral blood. Antigen-specific CD4+ T cells against citrullinated peptides also demonstrated a more naïve phenotype compared to those specific for viral peptides. RA was found to have higher frequency of CD4+PD-1highCXCR5- cells compared to seronegative or non-inflammatory conditions. Expanded CD4+ T cells positive for Vβ2 and Vβ14 TCR chains showed high frequencies of PD-1highCXCR5- and HLA-DR+CD27+ phenotypes. CONCLUSION: The presence of CD4+PD-1highCXCR5- CD4+ T cells (likely Tph) in the synovial fluid was significantly and specifically associated with seropositive RA. The phenotype of CD4+ T cells specific for citrullinated antigens in RA peripheral blood showed similarities to the phenotype of clonally expanded CD4+ with regards to the expression of HLA-DR and CD27. This could underlie a connection between antigen-specific cells and expanded CD4+ subsets in RA.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Anne Barton (Supervisor), Sebastien Viatte (Supervisor) & Tracy Hussell (Supervisor)