TREM2 and thoracic aortic aneurysm: •AAA tissue shows macrophage heterogeneity among 3 subtypes, with an increase in Trem2+ osteoclast-like Mø•Gene expression patterns and functions of AAA fibrocytes are distinct from Mø•Co-expression of Ptprc and Col1a2 is distinct to fibrocytes, separate from macrophages, fibroblasts, and SMCs; co-expression levels also identified fibrocytes in a scRNA-seq database of human ascending thoracic aortic aneurysm tissues•GFP-labeled fibrocytes were recruited to AAA tissues and attenuated AAA formation, growth, and elastin degradation