Accumulation of resident and peripheral dendritic cells in the aging CNS.

Dendritic cells (DC) are specialized antigen-presenting cells, responsible for peripheral immune responses. Recently, resident brain dendritic cells (bDC) were identified and functionally characterized in the young adult Itgax (CD11c) EYFP+ transgenic mouse brain. In the present study, we describe changes in number, phenotype, and source of bDC in the aging mouse brain. Immunohistochemistry and fluorescent activated cell sorting (FACS) analysis revealed an age-related increase in bDC with a concomitant rise in the expression of immune activation markers MHCII, CD80, and CD86. Quantification of immunolabeled bDC in the cortex, corpus callosum, and cerebellum of the aged brain revealed a 2- to 5-fold increase. In contrast, either no change or a decrease in bDC was noted in regions of adult neurogenesis. Chimeras (wild type host/EYFP+ bone marrow) suggest that the increase of EYFP+ cells in the aging brain is in part due to an accumulation of peripherally derived cells. Collectively, the numerical and phenotypic changes in bDC indicate these cells may serve as an important immune component in the functional and anatomic alterations associated with aging.