In vivo regulation of the assembly and intracellular transport of class I major histocompatibility complex molecules

Using H-2Kb-transfected Balb/c 3T3 cells which generate "empty" H-2Kb molecules devoid of antigenic peptides, we show that peptide availability determines the stability of class I molecules and dictates the overall intracellular transport rate of the class I complexes. Our data also indicate that chaperonin-like proteins are involved in class I assembly. Using Drosophila cells transfected with H-2Kb and murine beta 2-microglobulin, we show that one possible candidate, calnexin, associates with class I molecules prior to peptide acquisition. These data suggest that both peptide supply and assembly proteins dictate cell surface expression of class I major histocompatibility complex molecules and ultimately influence T cell recognition. The role of beta 2-microglobulin in class I assembly is also discussed.