APOE and atherosclerosis: In the present study, we constructed two lentiviral vectors to down-regulate the expression of Lp-PLA2 or YKL-40 following collar-induced atherosclerosis in apolipoprotein E-deficient (apoE-/-) mice and tested the hypothesis that knockdown of both YKL-40 and Lp-PLA2 together is more effective than knockdown of either alone in ameliorating atherosclerosis in apoE-/- mice.