CHI3L1 and Alzheimer disease: Other astrocytic signatures found in the post-mortem human brain of patients with AD vs age-matched controls include a reactive astrocytic state, denoted notably by a high expression of the astrocytic proteins GFAP and chitinase 3-like 1 (chi3l1 or YKL-40), which was observed in the temporal association cortex using cyclic multiplex fluorescent immunohistochemistry combined with spectral clustering analysis (Muñoz-Castro et al., 2022).