APOE and Alzheimer disease: To explore its relationship to systemic immune activation, we examined correlations between CHI3L1 and a panel of inflammatory gene transcripts, including IL1B, TNF, MMP9, LRP1, and TREM2. By characterizing peripheral CHI3L1 in AD continuum, we aimed to gain insight into systemic inflammatory gene signatures and to identify expression patterns relevant to APOE genotype, sex and clinical phenotype.