The costimulatory receptor CD28 and its inhibitory counterpart CTLA-4 share the same ligands and comprise a crucial checkpoint in T cell activation. CTLA-4 removes its ligands from antigen presenting cells by trans-endocytosis, which reduces the availability of costimulatory ligands for CD28 engagement to regulate T cell activation. This project examined the functional implications of reducing the availability of costimulatory molecules for CD4 T cell responses, and investigated the use of trans-endocytosis by other T cell receptors. Surprisingly, it was revealed that PD-1 and OX40 can also internalise their ligands, although perhaps not via the same mechanism as CTLA-4 trans-endocytosis. It was also shown that altering the availability of CD28 ligands affects the extent of T cell proliferation, suggesting that CTLA-4 trans-endocytosis can finely tune the T cell response. Furthermore, it was observed that CD28 costimulation is not always required for T cell activation and proliferation, but CD28 engagement is required for the optimal upregulation of a number of effector proteins and for TH2 cytokine production. Interestingly, T cells activated in the absence of CD28 signalling were not classically anergic. Strikingly, it was also found that memory T cells are dependent on CD28 costimulation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:619416 |
| Date | January 2014 |
| Creators | Briggs, Zoe Louise |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.bham.ac.uk//id/eprint/5378/ |
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