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Conventional dendritic cells (cDCs) generate protective cytotoxic T lymphocyte (CTL) responses against extracellular pathogens and tumors. This is achieved through a process known as cross-presentation (XP), and, despite its biological importance, the mechanism(s) driving XP remains unclear. Here, we show that a cDC-specific pore-forming protein called apolipoprotein L 7C (APOL7C) is up-regulated in response to innate immune stimuli and is recruited to phagosomes. Association of APOL7C with phagosomes led to phagosomal rupture and escape of engulfed antigens to the cytosol, where they could be processed via the endogenous MHC class I antigen processing pathway. Accordingly, mice deficient in APOL7C did not efficiently prime CD8 + T cells in response to immunization with bead-bound and cell-associated antigens. Together, our data indicate the presence of dedicated apolipoproteins that mediate the delivery of phagocytosed proteins to the cytosol of activated cDCs to facilitate XP.
Gonzales et al. (Fri,) studied this question.