H-2Kd protein is a major histocompatibility complex (MHC) class I molecule expressed in mice, particularly in BALB/c strains. It plays a critical role in antigen presentation by binding to antigenic peptides derived from pathogens, such as influenza nucleoprotein, and presenting them to CD8+ T cells to initiate an immune response. The crystal structure of H-2Kd in complex with beta-2 microglobulin and an influenza-derived peptide has been elucidated, revealing specific binding motifs and the structural basis for peptide recognition. This understanding is crucial for studies on immune responses and vaccine development.