Saraiva, L; (2014) Phagocytosis and MHC II antigen presentation by human gamma delta T cells. Doctoral thesis , UCL (University College London).

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Abstract

γδ T cells are a rare subset of T cells present in human blood and lymphoid tissues. Functionally, they stand at the interface of the innate and the acquired branch of the immune system as they express somatically rearranged antigen receptors but they also share many characteristics with NK cells. One of those is the ability to express CD16. CD16 is a cell-surface receptor that binds the Fc portion of IgG. In the isoform found on tissue macrophages and NK cells it is coupled to an intracellular signalling domain that allows it to initiate cellular processes leading to the internalisation of IgG-coated particles or cytotoxicity against IgG-coated cells. Therefore, it has a role in the clearance of IgG-coated complexes and the destruction of infected or malignant cells. In this thesis, I show that a population of γδ T cells present in human blood from healthy donors express the CD16 receptor and implicate a role for this receptor in phagocytosis of IgG-coated bacteria and synthetic beads coated with recombinant influenza M1 protein. These cells were subsequently shown to activate influenza-specific T cells through MHC II presentation. Importantly, neither αβ T cells nor NK cells were capable of significant phagocytosis. In addition, once CD11c+ cells had been removed from the NK fraction, neither αβ T cells or NK cells were capable of MHC II antigen presentation of influenza M1 antigen. The CD16+ γδ T cells displayed a phenotype of effector memory and late effector memory T cells suggesting a role for these cells in patrolling the blood and rapidly migrating to sites of inflammation for a combination of rapid effector and antigen presentation function.

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