Investigating the expression and function of IL-17A+ and IL-17F+ CD4+ T cells in human health and inflammatory arthritis

Abstract

IL-17A is a well-characterised pro-inflammatory cytokine, which has been implicated in the immunopathology of inflammatory arthritis. IL-17F is less well-studied. This thesis describes investigations into the phenotype of IL-17F+ CD4+ T cells, what drives IL-17F expression in CD4+ T cells and how IL-17F may contribute to inflammation. Healthy donor CD4+ T cells were cultured with IL-1β, IL-23, anti-CD3 mAb and anti-CD28 mAb, and cytokine expression was analysed by flow cytometry. In comparison to IL-17A+ IL-17F- CD4+ T cells, IL-17F+IL-17A- and IL-17A+IL-17F+ CD4+ T cells contained lower proportions of cells co-expressing IL-10 and higher proportions of cells co-expressing IFNγ. Titration of anti-CD28 mAb into healthy donor CD4+ T cell cultures revealed that strong co-stimulation increased the frequency of IL-17F+IL-17A- and IL-17A+IL-17F+ CD4+ T cells, whereas IL-17A+IL-17F- CD4+ T cell frequencies decreased. This was shown to be via an IL-2 dependent mechanism. To allow for the further characterisation of different IL-17A+ and IL-17F+ CD4+ T cell populations an IL-17A and IL-17F capture assay was developed in this thesis. Addition of human recombinant IL-17A, IL-17F and TNFα to synovial fibroblasts from patients with psoriatic arthritis (PsA) and rheumatoid arthritis (RA) resulted in significant production of IL-6. Combined blockade of IL-17A and IL-17F reduced IL-6 production to a larger extent than blockade of IL-17A alone, indicating IL-17F can contribute to inflammation. While IL-17A protein and IL-17A+ T cells were detected at increased levels in the inflamed joint of RA and PsA patients, little IL-17F protein and few IL-17F+ T cells were detected. Collectively, data presented in this thesis indicate that IL-17A and IL-17F are differentially regulated and that strong T cell stimulation induces IL-17F. Additionally, data suggests IL-17A+IL-17F-, IL-17F+IL-17A- and IL-17A+ IL-17F+ CD4+ T cells are functionally distinct. Finally, it is shown that in an environment where IL-17A and IL-17F are present dual blockade of IL-17A and IL-17F is more effective at reducing inflammation.

Date of Award	1 Jun 2019
Original language	English
Awarding Institution	King's College London
Supervisor	Leonie Taams (Supervisor)