Antigen-presenting cells (APCs) can prime allogeneic T cells or induce their tolerance to self-antigens. In Nature, McGovern et al. describe the functional properties of human fetal APCs. They identify dendritic cell (DC) subsets that mirror those found in adult tissues. While fetal DC subsets are capable of responding to Toll-like receptor ligands and priming allogeneic T cells in vitro, they induce more tolerogenic Foxp3+ regulatory T cells than adult DCs do. T cells cocultured with fetal DCs likewise proliferate less and produce fewer proinflammatory cytokines than T cells cultured with adult DCs. Fetal DCs express high amounts of arginase-2, which suppresses the expression of tumor necrosis factor. Thus fetal DCs are programmed to induce tolerogenic responses to allogeneic antigens encountered in utero.

Nature (14 June 2017) http://dx.doi.org/10.1038/nature22795