Dendritic cells (DCs) are instrumental in the initiation of T cell responses, but how thymic and peripheral tolerogenic DCs differ globally from Toll-like receptor (TLR)-induced immunogenic DCs remains unclear. Here, we show that thymic XCR1(+) DCs undergo a high rate of maturation, accompanied by profound gene-expression changes that are essential for central tolerance and also happen in germ-free mice. Those changes largely overlap those occurring during tolerogenic and, more unexpectedly, TLR-induced maturation of peripheral XCR1(+) DCs, arguing against the commonly held view that tolerogenic DCs undergo incomplete maturation. Interferon-stimulated gene (ISG) expression was among the few discriminators of immunogenic and tolerogenic XCR1(+) DCs. Tolerogenic XCR1(+) thymic DCs were, however, unique in expressing ISGs known to restrain virus replication. Therefore, a broad functional convergence characterizes tolerogenic and immunogenic XCR1(+) DC maturation in the thymus and periphery, maximizing antigen presentation and signal delivery to developing and to conventional and regulatory mature T cells.

Using a mouse model allowing inducible ablation of tissue-resident macrophages, Baranska et al. determine that skin macrophages are the only cells capable of capturing and retaining tattoo pigment particles and show that long-term tattoo persistence relies on macrophage renewal rather than on macrophage longevity.