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.