(A) Representative confocal images of aortic roots stained with CD68 (green), EYFP (yellow), and TdTomato (red) in BM chimeras of Ldlr^–/– mice reconstituted with BM from Cx3cr1^{CreERT2-IRES-YFP/+}Rosa26^{fl-tdTomato/+} mice (n = 3) gavaged with tamoxifen (TAM) at 14 and 15 weeks after feeding on a Western diet (WD) to label cells derived from CX3CR1⁺ monocytes. Scale bars: 50 μm. (B–F) Analysis of aortic arches by flow cytometry of Cx3cr1^{CreERT2-IRES-YFP/+}Rosa26^{fl-tdTomato/+} mice injected with AAV-PCSK9 and fed WD for 18 weeks before TAM treatment. Progression group mice (n = 4) were then kept on WD, while regression group mice were switched to chow and treated with ApoB-ASO for 2 weeks (n = 4). (B) Representative bright-field images and quantification of lesion areas of aortic roots. Scale bars: 50 um. (C) Density plot of t-distributed stochastic neighbor embedding (t-SNE) analysis of CD11b⁺TdTomato⁺ cells from aortic arches of mice in progression and regression groups subjected to aortic digestion. The aortic arches were analyzed by flow cytometry for expression of PD-L2, CD301, EYFP, F4/80, and MHCII markers (n = 8). (D) Heatmaps of geometric mean fluorescence, (E) quadrant plots, and (F) geometric MFI of PD-L2 and CD301 expression on CD11b⁺TdTomato⁺ cells from progression and regression groups in atherosclerotic Cx3cr1^{CreERT2-IRES-YFP/+}Rosa26^{fl-tdTomato/+} mice with AAV-mPCSK9 induction. Progression, n = 4–9; regression, n = 4–8. Statistical significance was calculated using Student’s t test, and data are presented as mean ± SEM (B and F). *P < 0.05, ***P < 0.001, ****P < 0.0001.