AREG and Alzheimer disease: In the scRNA-seq study of ascending thoracic aortic aneurysm by Li et al. (6), a group of macrophages seemed to have a transcriptome similar to that of cluster 2 in our study, both of which significantly expressed inflammatory factors and tissue repair cytokines, including TIMP1, VCAN, EREG, and AREG. The chronic nature of aortic aneurysm development suggests that this population of macrophages is already present in the aortic wall, even in the absence of the event of AD onset, which suggests that the expansion of cluster 2 in the AD tissue is not simply the consequence of AD onset.