Autophagy Receptors in the presentation of Viral antigens by MHC-II molecules

Abstract

CD4+ T lymphocytes play a major role in the establishment and maintenance of antiviral immunity. CD4+ T cells are activated by antigenic peptides, derived from pathogens, presented by MHC-II molecules. It is still widely assumed that CD4+ T cells recognize epitopes derived solely from exogenous viral particles or proteins. However, alternative sources of MHC-II-restricted antigens have been described. We showed that HIV-infected dendritic cells present MHC-II–restricted epitopes derived from newly synthesized proteins to HIV-specific CD4+ T cells. In fact, we confirmed that multiple cellular degradation pathways lead to endogenous presentation of MHC-II-restricted viral antigens, the generation of some viral epitopes being dependent and/or -independent on macroautophagy (herein referred as autophagy). We are charactering further these MHC-II-restricted endogenous presentation pathways. In particular, using RNA silencing, we asked whether autophagy receptors/adaptors that contribute to selective autophagy but also regulate endosome and autophagosome maturation might play a role. Surprisingly, although these receptors share a high structural homology and similar functions, we identified a single autophagy adaptor that strongly influences the presentation of viral antigens by MHC-II molecules. Although silencing of this autophagy adaptor does not impact the expression levels and the recycling of MHC-II molecules, it has a major influence on the ligandome of MHC-II molecules. In the absence of this adaptor, MHC-II molecules accumulate at the proximity of the nucleus in CD63+Lamp1+ acidified compartments. In addition, the lack of this autophagy adaptor has a strong influence on the invariant chain degradation and expression levels, strongly suggesting that it regulates the activation or traffic of vesicles involved in the processing of newly synthesised antigens. Interestingly, some viruses target these autophagy adaptors to favour viral replication. Our work might reveal new escape mechanisms developed by viruses to damper MHC-II restricted antigen presentation and immune responses.