CHI3L1 and amyotrophic lateral sclerosis: Similarly, ELISA validation for CHI3L1, a potential biomarker in the CSF of ALS patients thus far associated with astrocytes5,8, showed no release of CHI3L1 from MNs but a substantial secretion from microglia in monoculture, which was at lower levels in co-culture supernatants (Supp.