The present disclosure provides compositions, methods, systems, and devices for polynucleotide processing and analyte characterization from one or more cells. Such polynucleotide processing may be useful for a variety of applications, including characterization of major histocompatibility complex (MHC) molecules. The compositions, methods, systems, and devices disclosed herein generally describe peptides and barcoded oligonucleotides, which can be bound to a bead, such as a gel bead, useful for characterizing MHC molecules from one or more cells.