Peripherally-sourced myeloid antigen presenting cells increase with advanced aging.

Aging is associated with dysfunction of the gut microbiota-immune-brain axis, a major regulatory axis in both brain health and in central nervous system (CNS) diseases. Antigen presenting cells (APCs) play a major role in sensing changes in the gut microbiota and regulation of innate and adaptive immune responses. APCs have also been implicated in various chronic inflammatory conditions, including age-related neurodegenerative diseases. The increase in chronic low-level inflammation seen with aging has also been linked to behavioral decline. Despite their acknowledged importance along the gut microbiota-immune-brain axis, there is limited evidence on how APCs change with aging. In this study, we examined age-related changes in myeloid APCs in the gut, spleen, and brain as well as changes in the gut microbiota and behavioral phenotype in mice ranging in age from 2 months up to 32 months of both sexes. Our data show that the number of peripherally-sourced myeloid APCs significantly increases with advanced aging in the brain. In addition, our data showed that age-related changes in APCs are subset-specific in the gut and sexually dimorphic in the spleen. Our work highlights the importance of studying myeloid APCs in an age-, tissue-, and sex-specific manner.