Abstract
Type of funding sources: Foundation. Main funding source(s): Established Investigator of the Dutch Heart Foundation
Interleukin-18 (IL-18) is a pro-inflammatory cytokine and is secreted by macrophages after NLRP3-inflammasome activation. IL-18 is important for the induction of the Th1 response and overexpression of IL-18 aggravates atherosclerosis, suggesting that inhibition of IL-18 may act atheroprotective. In this study, we investigated the therapeutic potential of an IL-18 neutralizing antibody (anti-IL18) on atherosclerosis development.
Female ApoE-/- mice were fed a Western-type diet for 8 weeks and simultaneously received an antibody against IL-18 (100 µg/mouse; n=15) or a rat IgG2a control (100 µg/mouse; n=15) 3x per week intraperitoneally, after which the mice were sacrificed. First, we assessed macrophage phenotype in the peritoneal cavity. Expression of the proinflammatory markers CD80 (control: 46.3±1.4 *103; p<0.05 vs. anti-IL18: 40.4 ±1.7 *103) and iNOS (control: 15.5±1.8 *102 vs. anti-IL18: 8.0±1.9 *102; p<0.01) were reduced. In the aorta, MFIs of anti-inflammatory macrophage markers Arginase-1 (control: 389±99 vs. anti-IL18: 654±85; p=0.06) and CD206 (control: 55.2±2.4 *103 vs. anti-IL18: 62.8±3.7 *103; p=0.1) tended to be increased expression in the ascending aorta of anti-IL18 mice compared to controls. In addition, anti-IL18 treatment promoted the number of CD4 T cells (control: 20±1% vs. anti-IL18: 28±1%; p<0.0001) in the mediastinal lymph node and increased it’s regulatory phenotype (Tregs; Foxp3+) of CD4 (control: 23±1% vs. anti-IL18: 26±1%; p=0.07) and CD8 T cells (control: 0.4±0.02% vs. anti-IL18: 0.9±0.09%; p<0.0001). These effects however, did not translate into an effect on plaque size in the aortic root, as measured using an Oil-Red-O staining, which did not differ between the control and anti-IL18 treatment group (control: 47.1±2.4 *104 µm2 vs. anti-IL18: 43.4±2.3 *104 µm2).
Anti-IL18 treatment reduced the proinflammatory phenotype of peritoneal macrophages and promoted Tregs in the mediastinal lymph node. Further analyses on plaque stability and intraplaque macrophage subsets are currently being performed.
