Role of .beta.2-microglobulin in the intracellular processing of HLA antigens

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Abstract
The biosynthesis of HLA-A, -B and -C antigens was examined in the 2 Daudi and Raji lymphoblastoid cell lines. In Raji cells the HLA-A, -B and -C antigen H chains become core-glycosylated in the endoplasmic reticulum as evidenced by their sensitivity to endo-H digestion and tunicamycin treatment. .beta.2-Microglobulin is present in excess in the endoplasmic reticulum of the Raji cells and associates with the H chain at the time of synthesis of the H chain. Pulse-chase experiments demonstrated that the Raji HLA-A, -B and -C antigen H chains become terminally glycosylated since their changed characteristics included resistance to endo-H digestion, sensitivity to neuraminidase treatment and incorporation of fucose. Daudi HLA-A, -B and -C antigen H chains are synthesized normally and become core-glycosylated but not terminally glycosylated. Other glycosylated cell surface proteins, like the HLA-DR antigens, display normal glycosylation in Daudi cells. The absence of terminally glycosylated HLA-A, -B and -C antigen H chains is probably not the result of a general defect in the biosynthetic machinery of Daudi cells. Daudi cells lack the ability to synthesize .beta.2-microglobulin, the common subunit of all HLA-A, -B and -C antigens. Thus, .beta.2-microglobulin may be of importance for the intracellular transport of newly synthesized HLA-A, -B and -C antigens.

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