Biochemical characterization of CD1d expression in the absence of β2-microglobulin

CD1d is a major histocompatibility complex class I-like molecule that exhibits a distinct antigen processing pathway that functions in the presentation of hydrophobic antigens to T cells. CD1d has been previously shown to be expressed on the cell surface of human intestinal epithelial cell lines in vivo and a transfected cell line in vitro independently of beta(2)-microglobulin (beta(2)m). To define the relationship between CD1d and beta(2)m and characterize the biochemical structure of CD1d in the absence of beta(2)m, we have used a newly generated series of CD1d transfectants and CD1d-specific antibodies. These studies show that in the absence of beta(2)m, CD1d is expressed on the cell surface as a 45-kDa glycoprotein that is sensitive to endoglycosidase-H and is reduced to 37-kDa after N-glycanase digestion. In contrast, in the presence of beta(2)m, CD1d is expressed on the cell surface as a 48-kDa endoglycosidase-H-resistant glycoprotein. Pulse-chase metabolic labeling studies demonstrate that acquisition of endoglycosidase-H resistance of CD1d is observed in the presence of beta(2)m but not in the absence of beta(2)m even after a 24-h chase period. Thus, CD1d is able to be transported to the cell surface independently of beta(2)m; however, in the absence of beta(2)m, the glycosylation pattern of CD1d is altered and consistent with an immature glycoprotein.