Published:
[Erscheinungsort nicht ermittelbar]: University of New South Wales. Medical Sciences, 2019
Language:
English
Origination:
University thesis:
Dissertation, University of New South Wales. Medical Sciences, 2019
Footnote:
Description:
T cell activation is an essential part of the immune response and requires the activation of the T cell receptor (TCR) and co-receptors, including CD28. After ligand binding, these receptors are internalised into intracellular compartments, sorted for degradation or recycling back to the plasma membrane (PM). Endocytic trafficking plays a central role in the modulation of the immune response, as it regulates intensity and duration of receptor signalling. Much remains to be understood about how these processes are regulated for the TCR and CD28, which are crucial for an effective and sustained T cell activation. In this work, I developed and used a wide range of fluorescence microscopy approaches to investigate the endocytic pathways of TCR and CD28, which are detailed in chapter three. In chapter four, I contributed to decipher the regulation of TCR endocytic trafficking. My data showed, that TCR internalisation is clathrin independent and relies on dynamin for scission of the vesicle from the PM. My results further revealed that after endocytosis, TCR accumulates into an endosomal network which relies on the membrane-organising proteins flotillins. Finally, I contributed to show that flotillins promote sorting of TCR into a fast recycling pathway composed of Rab5 and Rab11-positive endosomes. In chapter five I aimed to understand the role of sorting nexin 9 (SNX9) in CD28 endocytosis. However, the results obtained point towards a different role for SNX9 in the regulation of the spatial organisation of CD28. My data showed that T cell activation leads to the de novo formation of an endosomal network demarked by SNX9. This network is proximal to the immunological synapse and does not extend inside the cell. Furthermore, SNX9 is also present at the PM where it strictly localises within CD28 clusters. I further showed that SNX9 is not required for CD28 clustering, recruitment to the PM or internalisation. Instead, SNX9 is necessary for the stability of CD28 clusters, phosphorylation and cellular signalling events downstream of CD28 activation such as T cell activation and IL-2 secretion. Altogether, my data shows that various endosomal networks regulate the spatial distribution of key T cell receptors.