Application of One-Dimensional Isoelectric Focusing to Separate Different Major Histocompatibility Complex Class I Alleles and Determine Their Allelic

Major histocompatibility complex class I (MHC-I) molecules are highly polymorphic cell surface expressed molecules that bind antigenic (Ag) peptides in the endoplasmic reticulum (ER) and transport them to the cell surface for presentation to cytotoxic T-cells (1 ). The MHC-I complex is composed of a 45 kDa polymorphic heavy chain (HC) noncovalently associated with the 12 kDa light chain, β₂ -microglobulin (β₂ m), together forming a peptide-receptive heterodimer (1 ). The third subunit is the Ag peptide, which is derived from cytosolic proteins and delivered into the ER by the peptide transporter associated with Ag processing, TAP (2 ). Correct assembly of the heterotrimeric MHC-I complexes in the ER is essential for their stable expression at the cell surface.