Viral proteins are usually processed by the ‘classical’ major histocompatibility complex (MHC) class I presentation pathway. Here we showed that although macrophages infected with herpes simplex virus type 1 (HSV-1) initially stimulated CD8+ T cells by this pathway, a second pathway involving a vacuolar compartment was triggered later during infection. Morphological and functional analyses indicated that distinct forms of autophagy facilitated the presentation of HSV-1 antigens on MHC class I molecules. One form of autophagy involved a previously unknown type of autophagosome that originated from the nuclear envelope. Whereas interferon-γ stimulated classical MHC class I presentation, fever-like hyperthermia and the pyrogenic cytokine interleukin 1β activated autophagy and the vacuolar processing of viral peptides. Viral peptides in autophagosomes were further processed by the proteasome, which suggests a complex interaction between the vacuolar and MHC class I presentation pathways.

Antigen presentation is essential for establishing immune tolerance and for immune responses against infectious disease and cancer. Although antigen presentation can be mediated by autophagy, here we demonstrate a pathway for mitochondrial antigen presentation (MitAP) that relies on the generation and trafficking of mitochondrial-derived vesicles (MDVs) rather than on autophagy/mitophagy. We find that PINK1 and Parkin, two mitochondrial proteins linked to Parkinson's disease (PD), actively inhibit MDV formation and MitAP. In absence of PINK1 or Parkin, inflammatory conditions trigger MitAP in immune cells, both in vitro and in vivo. MitAP and the formation of MDVs require Rab9 and Sorting nexin 9, whose recruitment to mitochondria is inhibited by Parkin. The identification of PINK1 and Parkin as suppressors of an immune-response-eliciting pathway provoked by inflammation suggests new insights into PD pathology.

and Michel Desjardins a,l,mPhagosomes, by killing and degrading pathogens for antigen presentation, are organelles implicated in key aspects of innate and adaptive immunity. Although it has been well established that phagosomes consist of membranes from the plasma membrane, endosomes, and lysosomes, the notion that the endoplasmic reticulum (ER) membrane could play an important role in the formation of the phagosome is debated. However, a method to accurately estimate the contribution of potential source organelles and contaminants to the phagosome proteome has been lacking. Herein, we have developed a proteomic approach for objectively quantifying the contribution of various organelles to the early and late phagosomes by comparing these fractions to their total membrane and postnuclear supernatant of origin in the J774A.1 murine macrophage cell line. Using quantitative label-free mass spectrometry, the abundance of peptides corresponding to hundreds of proteins was estimated and attributed to one of five organelles (e.g. plasma membrane, endosomes/lysosomes, ER, Golgi, and mitochondria). These data in combination with a stable isotope labeling in cell culture method designed to detect potential contaminant sources revealed that the ER is part of the phagosomal membrane and contributes ϳ20% of the early phagosome proteome. In addition, only a subset of ER proteins is recruited to the phagosome, suggesting that a specific subdomain(s) of the ER might be involved in phagocytosis. Western blotting and immunofluorescence substantially validated this conclusion; we were able to demonstrate that the fraction of the ER in which the ER marker GFP-KDEL accumulates is excluded from the phagosomes, whereas that containing the mVenus-Syntaxin 18 is recruited. These results highlight promising new avenues for the description of the pathogenic mechanisms used by Leishmania, Brucella, and Legionella spp

The classical view that endogenous antigens are processed by the proteasome and loaded on MHC class I molecules in the endoplasmic reticulum, while exogenous antigens taken up by endocytosis or phagocytosis are degraded and loaded on MHC class II in lysosome-derived organelles, has evolved along with the improvement of our understanding of the cell biology of antigen-presenting cells. In recent years, evidence for alternative presentation pathways has emerged. Exogenous antigens can be processed by the proteasome and loaded on MHC class I through a pathway called cross-presentation. Moreover, endogenous antigens can be targeted to lytic organelles for presentation on MHC class II through autophagy, a highly conserved cellular process of self-eating. Recent evidence indicates that the vacuolar degradation of endogenous antigens is also beneficial for presentation on MHC class I molecules. This review focuses on how various forms of autophagy participate to presentation of these antigens on MHC class I.

No abstract