THE ROLE OF BETA-2-MICROGLOBULIN IN PEPTIDE BINDING BY CLASS-I MOLECULES

Efficient transport of class I major histocompatibility complex molecules to the cell surface requires association of the class I heavy chain with endogenous peptide and the class I light chain, β2-microglobulin (β2M). A mutant cell line deficient in β2M transports low amounts of nonpeptide-associated heavy chains to the cell surface that can associate with exogenously provided β2M and synthetic peptide antigens. Normal β2M-sufficient cells grown in serum-free media devoid of β2M also require an exogenous source of β2M to efficiently bind synthetic peptide. Thus, class I molecules on normal cells do not spontaneously bind or exchange peptides.