Abstract Description MHCII molecules are traditionally associated with presenting extracellular antigens via endocytosis and the endo-lysosomal pathway. However, non-conventional MHCII pathways enabling intracellular proteins presentation are increasingly recognized. Evidence indicates that endogenous peptides presented by MHCII can drive autoimmunity by activating self-reactive T cells and play key roles in anti-tumor and anti-viral immunity. Understanding the mechanisms of endogenous antigen processing and presentation by MHCII is essential for advancing insights into immune responses and tolerance maintenance. While proteasome- and TAP-dependent pathways, as well as autophagy, contribute to MHCII endogenous antigen processing, many remain unexplored. A major challenge in studying these pathways, particularly for natural pathogen-derived epitopes, is the lack of specific detection tools. The influenza A PR8 neuraminidase (NA) epitope NA25 is endogenously processed and presented exclusively during live viral infection, absent with inactivated virus both in vivo and in vitro. Using a TCR-like antibody recognizing NA25 in complex with I-Ab, we performed a genome-wide CRISPR screen to identify regulators of NA25 presentation. This screening aims to reveal mechanisms underlying endogenous MHCII processing and presentation. Validated hits will be analyzed across PR8-derived endogenous epitopes in mouse models with diverse MHCII molecules to explore conservation across antigenic contexts. Funding Sources Supported by NIH 1R01AI180250 Topic Categories Antigen and Dendritic Cell Processing, Presentation, and Biology (AGDC)
Yang et al. (Sat,) studied this question.