CD9 and atherosclerosis: We also observed TREM2 and CD9 expression within this cluster, resembling the TREM2+ macrophages found in murine atherosclerosis.4,6 In other tissues, these TREM2+CD9+ macrophages have been described as either lipid-associated macrophages45 in obesity, or as scar associated macrophages44 in liver cirrhosis.