A major histocompatibility complex class Ib protein, CD1d, is expressed by human intestinal epithelial cells (IECs) and is a ligand for CD8+ T cells. CD1d was found to be expressed on the surface of human IECs as a 37-kilodalton protein that was β2-microglobulin (β2M) independent with no N-linked carbohydrate. Transfection into a β2M- cell line confirmed that CD1d could be expressed at the cell surface in the absence of β2M. These data indicate that IECs use a specialized pathway for CD1d synthesis and that a β2M-independent class Ib protein may be the normal ligand for some intestinal T cells.
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