The CD1 family of lipid antigen-presenting molecules

The paradigm that T cells recognize peptide antigens presented by major histocompatibility complex class I and class II molecules has been a guiding principle in the development of immunology. Here, Steven Porcelli and colleagues review studies that extend this paradigm by showing that CD1 proteins are a separate lineage of antigen-presenting molecules with unusually hydrophobic ligand-binding grooves that present nonpeptide lipid and glycolipid antigens to T cells.