APP and Alzheimer disease: To detect the distribution of total Aβ42, Aβ42Ms, and Aβ42Os in the intestinal systems and explore its potential correlation with the pathogenesis of AD, organs extracted from different parts of intestines (duodenum, jejunum, ileum, colon, and cecum) and their lysates from 3- and 9-month-old APP/PS1 mice were collected for 1F12/2C6 and 1F12/1F12 ELISA.