1A). Since IL-15 expression is also regulated at a post-translational level and is mainly GDC0199 membrane bound [5], we also determined the cell surface

expression of IL-15. Spleen cells and PBMCs were isolated from LDLr−/− mice which were fed a Western diet or a normal Chow diet for 10 weeks. FACS analysis showed that the percentage of IL-15 expressing cells within the spleen and PBMCs was highly elevated after 10 weeks of Western type diet (Fig. 1B; 12.59 ± 0.65% versus 26.07 ± 3.44%, P < 0.05 and 0.28 ± 0.06% versus 4.95 ± 0.98%, P < 0.05, respectively). We determined the effect of IL-15 on cell lines that represent the main cell types in the atherosclerotic lesion; macrophages (RAW cells), vascular smooth muscle cells (vSMCs) and endothelial cells (H5V cells). The relative expression is highest for macrophages (Fig. 2A), while also for vSMCs and endothelial cells a distinct expression is found. Addition of recombinant IL-15 to the various cell types induced only in macrophages an increased expression of tumor necrosis factor (TNF)-α on protein level (Fig. 2B). In line with the increase in TNF-alpha, we observed in macrophages a distinct increase in the pro-inflammatory cytokine IL-1β, whereas there was no significant effect seen on mRNA encoding IL-10 (Fig. 2C), IFN-γ or IL-12 (p40) (data not shown).

In addition, IL-15 significantly induced the expression of CXCL1, Forskolin mouse CCL2 and CCR2 in macrophages (Fig. 2D). These results indicate that IL-15 may affect the chemokines induced migration of macrophages [21]. Endothelial cells did not respond to IL-15 by upregulation of CXCL1, CCL2 or CCR2 on mRNA levels. In addition, IL-15 did not affect the expression of adhesion molecules such as VCAM-1, ICAM-1, PECAM and P-selectin in endothelial cells (data not shown). The Western-diet induced IL-15 expression on spleen cells and PBMCs and the IL-15 mediated

activation of macrophage stimulated us to analyze the effect of IL-15 blockade via vaccination. To this end, LDLr−/− mice were vaccinated against IL-15 by oral delivery using an attenuated strain of S. typhimurium transformed with an IL-15 expression vector (pcDNA3.1-IL-15) all or with S. typhimurium transformed with an empty vector (pcDNA3.1) as a control. This vaccination strategy leads to the induction of CD8+ cytotoxic T cells that specifically lyse those cells that overexpress IL-15 and present IL-15 peptides via MHC-I [19]. This protocol was used to study the role of VEGFR2 and CD99 in atherosclerosis [22] and [23]. Following vaccination, mice were fed a Western-type diet for 2 weeks and collars were placed around the carotid arteries which results in flow-induced atherosclerotic lesion formation [20]. A Subsequent to vaccination, we established the activation state of the CD8+ T cell population.