Lamina propria dendritic cells: for whom the bell TOLLs?

One of the major tasks of the mucosal immune system is to discriminate between dangerous and harmless antigens that are encountered daily at mucosal sites. In the gastrointestinal tract, immune cells have to tolerate food antigens and commensal microbes but at the same time have to induce a prompt response against invasive pathogens, when needed. In this issue of the European Journal of Immunology, it is shown that intestinal dendritic cell (DC) populations can be distinguished based on the expression level of Toll-like receptors (TLR) and on the response of these TLR to their microbial ligands. DC either do not express TLR or they express them but respond in a non-inflammatory mode. In this commentary, these findings are discussed in the context of available knowledge on lamina propria DC.