CD4 and Alzheimer disease: We further treated 3-month-old APP-transgenic mice expressing Il-17a-eGFP reporter43 with and without antibiotics, and observed that depletion of gut bacteria for 2 months significantly reduced eGFP-expressing CD4+ lymphocytes in both lamina propria and Peyer’s patches of the gut compared to control AD mice with normal drinking water (Figure 2e–h; t test, p < 0.05).