Two Conformations of L^d Distinguished by Their Abilities to Bind β ₂-Microglobulin Are Synthesized, Processed, and Expressed on the Cell Surface

Abstract

Many theories have emerged regarding the role of β ₂-microgIobulin (β ₂m) in the synthesis and cell surface expression of class I molecules. Perhaps the most widespread theory is that β ₂m is required for cell surface expression of class I molecules. It has been proposed that β ₂m may act as a transport protein for class I molecules that facilitates their intracellular trafficking from the rough endoplasmic reticulum (ER) to the Golgi apparatus (Krangel et al. 1979). These conclusions are based primarily on studies using the human Burkitt’s lymphoma Daudi. Daudi cells were found not to produce β ₂m protein and not to express detectable class I molecules on the cell surface (Goodfellow et al. 1975). To establish the cause and effect of these observations, cytoplasmic class I proteins were detected in Daudi and surface expression of class I antigens could be rescued by fusion to β ₂m⁺ cell types (Fellous et al. 1977; Arce-Gomez et al. 1978).