Single-cell profiling reveals inflammatory polarization of human carotid versus femoral plaque leukocytes

Rationale: Femoral atherosclerotic plaques are less inflammatory than carotid plaques histologically, but limited cell-level data exist regarding comparative immune landscapes and polarization at these sites. Objectives: We investigated intraplaque leukocyte phenotypes and transcriptional polarization in 49 total patients undergoing femoral (N=23) or carotid (N=26) endarterectomy using single-cell ribonucleic acid sequencing (scRNA-seq; N=13), flow cytometry (N=24), and immunohistochemistry (N=12). Findings: Comparative scRNA-seq of CD45 positive-selected leukocytes from femoral (N=9; 35265 cells) and carotid (N=4; 30655 cells) plaque revealed distinct transcriptional profiles. Inflammatory foam cell-like macrophages and monocytes comprised 2.5- to 4-fold higher proportions of myeloid cells in carotid plaques, whereas non-inflammatory foam cell-like macrophages and LYVE1-overexpressing resident-like macrophages comprised 3.5- to 9-fold higher proportions of myeloid cells in femoral plaque (p<0.001 for all). A significant comparative excess of CCR2+ macrophages in carotid versus femoral plaque was observed by flow cytometry in a separate validation cohort. B cells were more prevalent and exhibited a comparatively anti-inflammatory profile in femoral plaque, whereas cytotoxic CD8+ T cells were more prevalent in carotid plaque. Conclusion: Human femoral plaques exhibit distinct macrophage profiles and diminished CD8+ T cell populations compared with carotid plaques. Experimental models elucidating determinants of plaque site-specific cell polarization cues are warranted.