1. Département de pathologie et biologie cellulaire, Université de Montréal, C.P.6128, Succ centre-ville, Montréal, Québec, H3C 3J7, Canada
2. Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
3. Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
4. Caprion Pharmaceuticals Inc., Montréal, Québec, H45 2C8, Canada
5. These authors contributed equally to this work

Correspondence to: Michel Desjardins^1,4 Email: michel.desjardins@umontreal.ca

The ability to process microbial antigens and present them at the surface of cells is an important aspect of our innate ability to clear infections. It is generally accepted that antigens in the cytoplasm are loaded in the endoplasmic reticulum and presented at the cell surface on major histocompatibility complex (MHC) class I molecules, whereas peptides present in endo/phagocytic compartments are presented on MHC class II molecules^{1, 2}. Despite the apparent segregation of the class I and class II pathways, antigens from intracellular pathogens including mycobacteria, Escherichia coli, Salmonella typhimurium, Brucella abortus and Leishmania, have been shown to elicit an MHC class-I-dependent CD8⁺ T-cell response^{3, 4, 5, 6, 7}, a process referred to as cross-presentation². The cellular mechanisms allowing the cross-presentation pathway are poorly understood. Here we show that phagosomes display the elements and properties needed to be self-sufficient for the cross-presentation of exogenous antigens, a newly ascribed function linked to phagocytosis mediated by the endoplasmic reticulum.