MHC Class I Internalization via Autophagy Proteins

Macroautophagy is a ubiquitous degradative pathway involved in innate and adaptive immunity. Its molecular machinery has been described to deliver intracellular and extracellular antigens to MHC class II loading compartment by regulating autophagosome and phagosome maturation. We recently found that the respective Atg proteins can contribute to MHC class I-restricted antigen presentation to CD8⁺ T cells by regulating MHC class I surface levels in mouse dendritic cell. Indeed, we determined that MHC class I molecules are stabilized on the cell surface of murine antigen presenting cells deficient for core components of the macroautophagy machinery such as Atg5 and Atg7. This stabilization seems to result from defective internalization of MHC class I molecules dependent on adaptor protein kinase 1 (AAK1), involved in clathrin-mediated endocytosis. Moreover, macroautophagy-dependent stabilization of MHC class I molecules leads to enhanced CD8⁺ T cell priming during influenza A virus infection in vivo, resulting in decreased pathology. In this chapter, we describe four experiments to monitor, characterize, and quantify the effect of macroautophagy deficiency on MHC class I molecule trafficking and the subsequent CD8⁺ T cell priming. First, we will show how to monitor MHC class I internalization in lung CD11c⁺ cells from mice lacking key components of the macroautophagy machinery. Then, we will propose a method to characterize the interaction between either MHC class I or Atg8/LC3 with AAK1. Finally, we will describe how to evaluate the influenza A-specific CD8⁺ T cell response in mice conditionally depleted for Atg5 in their DC compartment. This set of experiments allows to characterize MHC class I internalization with the help of the molecular machinery of macroautophagy.