Sofía C. Khouili, Elena Priego, Ignacio Heras‐Murillo, Gillian Dunphy, Annalaura Mastrangelo, Sarai Martínez-Cano, Vanessa Nuñez, Manuel Rodrigo-Tapias, Adrián Belinchón-García, Johan Garaude, Salvador Iborra, Navdeep S. Chandel, Patricia González‐Rodríguez, Michel Enamorado, David Sancho
Mitochondrial metabolism modulates immune cell signaling, yet how individual electron transport chain complexes fine-tune dendritic cell (DC) function remains unclear. Here, we identify mitochondrial complex I (CI) as a critical metabolic checkpoint controlling antigen cross-presentation by DCs in mice. Deficiency of the CI subunit NDUFS4 in DCs led to the formation of a nonfunctional CI subcomplex, resulting in mildly impaired mitochondrial respiration without triggering a compensatory glycolytic shift. NDUFS4 deficiency limited endosomal escape of internalized antigens, thereby impairing antigen cross-presentation while largely preserving direct presentation. CI dysfunction lowered the NAD + /NADH ratio, concomitant with decreased ATP levels, and diminished neutral lipid storage and lipid peroxidation. Restoration of the NAD + /NADH ratio rescued cross-presentation in NDUFS4-deficient DCs. NDUFS2-deficient DCs showed similar defects in cross-presentation, which were also rescued by rebalancing the NAD + /NADH ratio. Together, these findings reveal a link between mitochondrial CI integrity, NAD + -driven redox metabolism, and antigen cross-presentation.