PIs: Bradshaw, Elizabeth M., Ph.D. and Wassim Elyaman, Ph.D. Title: Microglia antigen presentation in the CNS of Alzheimer's disease Project Summary/Abstract Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive decline and dementia. Genome-wide association studies have identified novel AD susceptibility loci. Interestingly the associated genes at several of these loci implicate the immune system in late-onset AD (LOAD), specifically the innate immune system, including the human leukocyte antigen (HLA) region. The finding of the HLA region being genetically associated with LOAD further emphasizes the question of how microglia, the antigen-presenting cells of the central nervous system (CNS), interact with infiltrating T cells, which have been observed in the hippocampus of AD patients, and specifically what antigens are being presented. In parallel, the pathogen hypothesis has garnered more support for a possible pathogenic etiology of AD. We propose to leverage our understanding of the immune system combined with cutting-edge technology and access to AD patient blood and brain autopsies to determine if these neuroinvasive pathogens are neurovirulent in AD. For this application, we propose a multifaceted approach to: 1) identify the peptides being presented by the MHC of microglia in the AD brain in regions of high T cell infiltration and areas of low T cell infiltration; 2) examine the antigen reactivity and phenotype of T cells infiltrating the hippocampus in AD, and 3) determine how microglia function as antigen-presenting cells of pathogens to infiltrating T cells.