The molecular basis of CD 1 ‐mediated presentation of Iipid antigens

Publisher Website
Google Scholar
Abstract
Summary: The CD1 family of proteins mediates a newly described pathway for presentation of lipids and glycolipids for specific recognition by T cells. All four of the known human CD1 proteins (CD1a, CD1b, CD1c and CD1d) as well as murine CD Id have now been shown to mediate T‐cell recognition of lipid or glycolipid antigens. These antigens include naturally occuring foreign glycolipids from intracellular pathogens or synthetic glycolipids that are related in structure to mammalian glycolipids. The CD l b and CD I d‐presented antigens differ in their fine structures but reveal a general motif in which a rigid hydrophilic cap is botind to two aliphatic hydrocarbon chains. Different T‐cell populations recognize individual antigens without cross‐reactivity to closely related antigen structures or CD 1 isoforms, documenting the complexity and fine specificity of CD l‐mediated T‐cell responses. Mapping of the molecular detertninants of recognition for CD 1 b and CD 1d‐preseced antigens reveals that T cells discriminate the fine structure of the hydrophilic cap of the antigen, but both the length and structure of the lipid chains may be altered without loss of recognition. This pattern of lipid antigen recognition may be accounted for by a simple molecular mechanism of presentation that parallels the known mechanism for presentation of peptides, but solves the special problems related to the hydrophobic chemical nature of the lipid antigens. We propose that CD 1 binds antigen by accommodating the two lipid tails within the hydrophobic groove of its two membrane distal domains, positioning the rigid hydrophilic cap of the antigen on the solvent‐exposed surface of the CD1 protein, where it can directly contact the T‐cell antigen receptor. This model provides a molecular basis for recognition of a new and diverse set of T‐cell antigens contained within the lipid bilayers of cellular membranes.