Gros et al. showed that in cross-presenting cDC1s, as compared to cDC2s, the efficient export of antigens to the cytosol was associated with a higher frequency of endolysosomal rupture and recruitment of endosomal sorting complex required for transport (ESCRT)-III, the major endocytic intracellular membrane repair system. shRNA silencing of ESCRT-III induced RIPK3/MLKL-dependent necroptotic processes and persistence of unrepaired, permeable endomembranes, which allowed unrestrained leakage/export of less degraded, large branched or folded antigens into the cytosol for enhanced antigen cross-presentation in vitro and in vivo.
Contributed by Paula Hochman
ABSTRACT: Despite its crucial role in initiation of cytotoxic immune responses, the molecular pathways underlying antigen cross-presentation remain incompletely understood. The mechanism of antigen exit from endocytic compartments into the cytosol is a long-standing matter of controversy, confronting two main models: transfer through specific channels/transporters or rupture of endocytic membranes and leakage of luminal content. By monitoring the occurrence of intracellular damage in conventional dendritic cells (cDCs), we show that cross-presenting cDC1s display more frequent endomembrane injuries and increased recruitment of endosomal sorting complex required for transport (ESCRT)-III, the main repair system for intracellular membranes, relative to cDC2s. Silencing of CHMP2a or CHMP4b, two effector subunits of ESCRT-III, enhances cytosolic antigen export and cross-presentation. This phenotype is partially reversed by chemical inhibition of RIPK3, suggesting that endocytic damage is related to basal activation of the necroptosis pathway. Membrane repair therefore proves crucial in containing antigen export to the cytosol and cross-presentation in cDCs.