CTSS and Alzheimer disease: Importantly, this study incorporated the Alzheimer’s disease Immunization and Microbiota Initiative study Cohort (ADIMIC) to further validate the alterations of blood cathepsin expression level and examine their correlation with cognitive level and plasma AD-related pathological markers (Aβ40, Aβ42, Aβ42/40, p-Tau181, glial fibrillary acidic protein (GFAP), and neurofilament light (NFL)).