HLA-DO expression favors the presentation of DM-susceptible viral peptides in B cells 2860

Abstract Description Exogenous antigens internalized by B cells are trafficked to endosomal compartments for processing and loading onto MHCII. The non-classical MHCII molecule HLA-DM (DM) binds to MHCII and catalyzes peptide exchange favoring the loading of peptides with a higher affinity to MHCII. HLA-DO (DO) conditionally binds to and blocks a fraction of DM in B cells. At steady state, DM activity is lower compared to activated APCs and the expression of DM prevents the presentation of certain cryptic epitopes from exogenous antigens, but favors the presentation of immunodominant epitopes. Previous work from our lab demonstrated that DO expressing B cells present a greater diversity of self-peptide sequences favoring low-affinity peptides. Here we investigated if DO expression altered the presentation of self, bovine and influenza derived peptides in virally-infected cells using qualitative and quantitative mass spectrometry approaches. We infected LG-2 WT and KO cells with two influenza strains and performed DDA, DIA and PRM mass spectrometry to record the viral peptide sequences. We observed that DO expression increased the viral peptide diversity correlated with susceptibility to DM-editing. Using DIA-MS and PRM-MS approaches, we further observed that cells expressing DO favored the presentation viral peptides with higher susceptibility to DM-editing. Our study expands on the viral peptidome and a DM-dependent peptide selection mechanism for DO. Funding Sources NIH AI127869 (Stern) Topic Categories Antigen and Dendritic Cell Processing, Presentation, and Biology (AGDC)