Collins, NicholasJiang, XiaodongZaid, AliMacleod, Bethany L.Li, JanePark, Chang OokHaque, AshrafulBedoui, SammyHeath, William R.Mueller, Scott N.Kupper, ThomasGebhardt, ThomasCarbone, Francis R.2016-06-142016Collins, N., X. Jiang, A. Zaid, B. L. Macleod, J. Li, C. O. Park, A. Haque, et al. 2016. “Skin CD4+ memory T cells exhibit combined cluster-mediated retention and equilibration with the circulation.” Nature Communications 7 (1): 11514. doi:10.1038/ncomms11514. http://dx.doi.org/10.1038/ncomms11514.2041-1723http://nrs.harvard.edu/urn-3:HUL.InstRepos:27320212Although memory T cells within barrier tissues can persist as permanent residents, at least some exchange with blood. The extent to which this occurs is unclear. Here we show that memory CD4+ T cells in mouse skin are in equilibrium with the circulation at steady state. These cells are dispersed throughout the inter-follicular regions of the dermis and form clusters with antigen presenting cells around hair follicles. After infection or administration of a contact sensitizing agent, there is a sustained increase in skin CD4+ T-cell content, which is confined to the clusters, with a concomitant CCL5-dependent increase in CD4+ T-cell recruitment. Skin CCL5 is derived from CD11b+ cells and CD8+ T cells, with the elimination of the latter decreasing CD4+ T-cell numbers. These results reveal a complex pattern of tissue-retention and equilibration for CD4+ memory T cells in skin, which is altered by infection and inflammation history.en-USJournal Article2016-06-1410.1038/ncomms11514