Studies in murine models demonstrate that AD-susceptible mice, known as 5xFAD mice that express five human AD-linked transgenes in APP and PSEN1, have more rapid disease progression when their adaptive immune system is genetically ablated (Rag2−/−/Il2rγ−/−-5xFAD mice), suggesting a protective role for adaptive immunity in the diseased brain. The gene discussed is PSEN1; the disease is Alzheimer disease.