How dietary lipids and membrane order affect T cell function in vivo

As the T cell receptor and many of the associated signalling molecules are embedded within the plasma membrane, it has been hypothesised that plasma membrane lipids, and associated lipid ‘ordered’ membrane domains, play a role in regulating T cell signalling. The first aim of this thesis was to examine in mice whether dietary lipids influence the lipid composition of T cells and thus membrane order, and how this correlates to in vivo and ex vivo T cell responses. Chapters 3 and 4 describe both acute and long-term dietary studies, which involved feeding C57BL/6J and LDLR-/- mice a high-fat or high-cholesterol diet. A contact hypersensitivity (CHS) reaction was then induced using 1-fluoro-2,4-dinitrobenzene and the CD4+ and CD8+ T cell responses examined in the draining lymph nodes by flow cytometry. The in vivo T cell responses were correlated to the cellular lipid content of splenic T cells using mass spectrometry, and membrane order measured with Laurdan microscopy. Finally, the activation response of ex vivo stimulated splenic T cells was assessed with qRT-PCR. Both the C57BL/6J and LDLR-/- dietary studies illustrated that long-term high-fat or high-cholesterol feeding significantly increased both CD4+ and CD8+ T cell proliferation, and central-memory CD4+ T cell production, within the draining lymph nodes following CHS. This was associated with changes in cellular phospholipids, fatty acids and cholesterol, as well as alterations in membrane order at the T cell activation site, and reduced IL-2 mRNA production. The last results chapter of this thesis, chapter 5, focused directly on how membrane order impacts on T cell function in vivo. Using an adoptive transfer system, CD4+ T cells from OT-II transgenic mice were treated with the oxysterol 7-ketocholesterol, which perturbs membrane condensation, or a cholesterol control, before transfer into B6.SJL recipient mice. I then challenged the recipients with ovalbumin323–339 to measure antigen-specific CD4+ T cell responses by flow cytometry, which were again correlated the sterol content of ex vivo manipulated cells. Our results were inconsistent but suggest that both 7KC and cholesterol treatment cause a reduction in OVA-specific CD4+ T cell proliferation within the draining lymph nodes of recipient mice