Deleting interleukin-10 from myeloid cells exacerbates atherosclerosis in Apoe^-/- mice

Atherosclerosis is initiated by subendothelial retention of lipoproteins and cholesterol, which triggers a non-resolving inflammatory process that over time leads to plaque progression in the artery wall. Myeloid cells and in particular macrophages are the primary drivers of the inflammatory response and plaque formation. Several immune cells including macrophages, T cells and B cells secrete the anti-inflammatory cytokine IL-10, known to be essential for the atherosclerosis protection. The cellular source of IL-10 in natural atherosclerosis progression is unknown. This study aimed to determine the main IL10-producing cell type in atherosclerosis. To do so, we crossed VertX mice, in which IRES-green fluorescent protein (eGFP) was placed downstream of exon 5 of the Il10 gene, with atherosclerosis-prone Apoe^-/- mice. We found that myeloid cells express high levels of IL-10 in VertX Apoe^-/- mice in both chow and western-diet fed mice. By single cell RNA sequencing and flow cytometry analysis, we identified resident and inflammatory macrophages in atherosclerotic plaques as the main IL-10 producers. To address whether IL-10 secreted by myeloid cells is essential for the protection, we utilized LyzM^Cre+Il10^fl/fl mice crossed into the Apoe^-/- background and confirmed that macrophages were unable to secrete IL-10. Chow and western diet-fed LyzM^Cre+Il10^fl/fl Apoe^-/- mice developed significantly larger atherosclerotic plaques as measured by en face morphometry than LyzM^Cre-Il10 ^fl/flApoe^-/-. Flow cytometry and cytokine measurements suggest that the depletion of IL-10 in myeloid cells increases Th17 cells with elevated CCL2, and TNFα in blood plasma. We conclude that macrophage-derived IL-10 is critical for limiting atherosclerosis in mice.