CHI3L1 and neurodegenerative disease: Finally, there are a number of relevant microglial activation markers: sTREM2 (soluble TREM2), which is associated with microglial activation in AD; YKL-40 (Chitinase-3-like protein 1), which is elevated in various neurodegenerative diseases; Iba1 (ionized calcium-binding adapter molecule 1), which is detectable in CSF; and TSPO (Translocator Protein), which is used in PET imaging to measure microglial activation [165].