In our study, we found no correlation between plasma IgA levels and Q-albumin ratio, and the Q-albumin ratio did not differ between NC and AD patients in cohort I. However, previous studies have demonstrated an increased Ig immunoreactivity and the presence of Ig+ neurons and glial cells in postmortem AD brains in association with BBB [43, 48–50]. Here, ALB is linked to Alzheimer disease.