When compared to healthy controls, COVID-19 groups <50 years old exhibited a decreasing autoantibody level targeting amyloid β peptide, β catenin, claudin 5, enteric nerve, epithelial cell antigen, fibulin, glutamic acid decarboxylase, insulin receptor, liver microsomal antigen, transglutaminase 3, transglutaminase 6, and zonulin in accordance with COVID-19 severity (aging effect 1). Here, CLDN5 is linked to COVID-19.