The impact of endoplasmic reticulum stress responses in dendritic cell immunobiology.

Dendritic cells (DCs) are critical for bridging innate and adaptive immunity. They do so by presenting antigens to T cells, and by expressing diverse molecules that further promote T cell activation, differentiation and memory formation. During this process, intracellular and extracellular factors can perturb the protein-folding capacity of endoplasmic reticulum (ER) and induce a cellular state of "ER stress," which is controlled and resolved by the unfolded protein response (UPR). Interestingly, various studies have shown that DCs can activate UPR-related pathways even in the absence of global ER stress, and that this process can modulate their normal activity. In other settings, such as cancer, adverse microenvironmental conditions have been demonstrated to evoke severe ER stress and persistent activation of the UPR in tumor-infiltrating DCs. This process disrupts their metabolism and local antigen-presenting capacity, hence impeding the initiation and maintenance of anti-cancer immunity. Here, we review recent findings on how canonical and non-canonical UPR activation impacts DC immunobiology at the steady-state, upon activation via pattern recognition receptors, and under diverse pathological conditions. We also discuss the potential therapeutic implications that targeting the UPR in DCs may have in the context of cancer and in other pathologies such as graft-versus-host disease.