Characterisation of T cell surface phenotype and effector function in a surrogate model of rheumatoid arthritis

Abstract

TNFα plays a pivotal role in the pathogenesis of rheumatoid arthritis (RA), however the mechanisms underlying its dysregulation are not completely understood. TNFα production by macrophages is dependent on their contact with synovial T cells. In an in vitro model of RA, peripheral blood lymphocytes stimulated with a cocktail of cytokines mimic this RA T cell effector function. This thesis defines and characterises the effector population of cytokine-activated human T cells through two different approaches. Studies presented here show that within a population of cytokine-activated T cells, CD4+CD45RO+CCR7- cells induce the highest levels of TNFα when co-cultured with monocytes. Cytokine-activated CD4+ memory T cells phenotypically and functionally resemble lymphocytes isolated from RA synovial tissue. The cytokine cocktail induces proliferation and differentiation of peripheral blood T cells into highly potent effectors. These cells upregulate specific activation markers, adhesion molecules and chemokine receptors; such as CD25, CD69, CD62L, VLA-4, LFA-1 and CXCR4 which directly or indirectly, contribute to the induction of TNFα. By defining the phenotype of the lymphocytes most capable of inducing TNFα in our model, I isolated a population of T cells on which to focus my studies. The molecular nature of contact-dependent monocyte activation by cytokineactivated T cells was further investigated through proteomic profiling of the T cell surface. Plasma membrane protein-enriched samples were resolved in one- and two-dimensions. Subsequent mass spectrometry identified two molecules of interest. CD97 was found to be highly expressed by cytokine-activated CD4+ memory T cells, and contributed to both the induction of monocyte TNFα and spontaneous TNFα release from rheumatoid synovial tissue. Expression of CD81 and other tetraspanin family members increased on cytokine activation and was observed in synovial tissue. The results presented in this thesis provide further insight into the contribution of T cells in RA.