NK cell mediated lysis of vascular smooth muscle cells in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) are characterised by a chronic inflammatory infiltrate within the abdominal aortic wall and aortic smooth muscle cell (AoSMC) apoptosis. It is postulated that the inflammatory infiltrate causes AoSMC apoptosis, with resultant aortic wall weakening and aneurysmal degeneration. This putative immune-mediated reaction against aortic wall component suggests that AAA may have features of an auto immune disease. It has been previously demonstrated that natural killer (NK) cells are elevated in the peripheral blood (PB) of AAA patients and display increased cytotoxicity against AoSMC. This study aimed to identify the molecular basis of the increased NK cell cytotoxicity and why an immune-mediated reaction occurs against AoSMC. Using multi-parametric flow cytometry (FC), expression of the activatory receptors NKp30, NKp44, NKp46 and NKG2D were analysed on PB NK cells from AAA patients and age-sex-matched healthy controls. No difference in activatory receptor expression or cell surface density (ΔMFI) existed between the two groups. Region specific (intra-luminal blood and AAA tissue) activatory receptor phenotypes were also investigated in AAA patients. The significant finding was a reduction in the ΔMFI of NKG2D on tissue NK cells, suggesting an interaction between this receptor and potential cognate ligands within the aortic wall. Characterised AoSMC explanted from AAA tissue were subjected to analysis using qRT-PCR and FC to identify the expression of death receptors (Fas, TRAIL-RI and TRAIL R2) and NKG2D ligands (MICA, MICB, ULBPI-3). AoSMC expressed mRNA for all NKG2D ligands. FC confirmed the cell-surface expression of NKG2D ligands and the death receptors. A significantly greater percentage of NK cells from AAA patients were CD107a+ when co-cultured with AAA AoSMC, thus accounting for the increased cytotoxicity in this group. Despite using anti-NKG2D it was not possible to inhibit NK cell degranulation in response to the NKG2D ligands on AoSMC. This work has demonstrated that AoSMC from AAA express death receptors and NKG2D ligands, potentially accounting for the NK cell molecular mechanism that leads to AoSMC apoptosis. The expression of NKG2D ligands, which have been demonstrated in other auto immune diseases, favours the hypothesis that AAA are an immune-mediated process directed against the abdominal aortic wall.EThOS - Electronic Theses Online ServiceGBUnited Kingdo