The researchers created an atlas of chromatin accessibility from approximately 7 million cells from 21 tissues in mammals of three age groups of both sexes.[2][3] The atlas revealed 536 major cell types and 1828 subtypes defined by unique chromatin landscapes at approximately 1.3 million cis-regulatory elements.[2][3] With aging, there is extensive remodeling of immune lineages with an increase in plasma cells and macrophages and a decrease in T and B cell progenitors.[2][3] Among non-immune cells, the populations of kidney podocytes, ovarian granulosa cells, muscle tenocytes and lung aerocytes decreased significantly.[2][3] Many cell subtypes changed synchronously across multiple organs, suggesting the influence of systemic signals.[1][2] At the molecular level, thousands of regions of differential chromatin accessibility have been identified, including changes in spikes and motifs of transcription factors associated with inflammatory and developmental genes.[1][2] Approximately 40% of the changes in cell populations were sex-dependent, with tens of thousands of spikes altered exclusively in one sex.[1][2] These findings provide a framework for understanding aging and a resource for therapeutic strategies.[1][3]