To further analyse the potential effect of APOEε4 on IgA levels in relation to AD pathology, we divided the cohorts based on APOEε4 status and investigated the differences between clinical diagnoses as well as associations between plasma IgA levels and cognition, CRP, and CSF AD biomarkers in cohort I and neuropathology and brain IgA immunoreactivity in cohort II. The gene discussed is CRP; the disease is Alzheimer disease.