Fcγ receptors (FcγR) which recognize the Fc fraction of IgG play key roles in the modulation of a range of cellular responses as part of the host defense against foreign microbes and antigens. An important function of FcγR is to mediate internalization of soluble IgG-containing immune complexes via endocytosis. The mechanisms of internalization and intracellular transport of FcγR after internalization are less clear. In this thesis, I investigated the trafficking behaviours of human FcγRIIA and FcγRIIB2 upon clustering with immune complexes. In Chapter 3, I demonstrate FcγRIIA, when engaged with multivalent heat aggregated IgG (agIgG), is delivered along with its ligand to lysosomal compartments for degradation, whereas FcγRIIB2 becomes dissociated from the ligand and routed separately into a recycling pathway. FcγRIIA sorting to lysosomes requires receptor multimerization, but does not require either Src family kinase (SFK) activity or receptor ubiquitylation. Upon co-engagement, these two receptors are sorted independently to distinct final fates after dissociating from their co-clustering ligand. In Chapter 4, I show that while the ubiquitin-conjugating system is required for FcγRIIA-mediated endocytosis, it is not required for FcγRIIB2 endocytosis. FcγRIIB2 internalizes immune complexes at a faster rate than FcγRIIA and accelerates the endocytosis of FcγRIIA upon receptor co-engagement. Taken together, these results reveal fundamental differences in the trafficking behaviour of FcγRIIA and FcγRIIB2 both during the initial induction of endocytosis as well as during subsequent intracellular sorting.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35753 |
| Date | 26 July 2013 |
| Creators | Zhang, Christine |
| Contributors | Booth, James |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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