Recognition of lipid antigens by T cells

Publisher Website
Google Scholar
Abstract
Lipid antigens are immunogenic for T cells when they are presented by CD1 antigen-presenting molecules that bind lipids. Five CD1 proteins are expressed in humans, whereas only one is expressed in mice. Lipid molecules are not soluble in water and are always associated with membranes or lipid-binding proteins in tissues and biological fluids. This characteristic makes the biology and immunogenicity of lipids different from that of peptides. Microbial and self lipid antigens have been identified. Intracellular microorganisms that infect antigen-presenting cells and localize in the phagosomes release immunogenic lipids, which travel to the compartments where they intersect with recycling CD1 molecules. Complex glycolipids become stimulatory after processing and loading onto CD1 molecules in endosomal compartments. Both of these events are assisted by lipid-transfer proteins, which are necessary and redundant. Lipid-specific T cells can use both T-cell receptor (TCR)-αβ and TCR-γδ, do not preferentially express CD4 or CD8 co-receptors, are selected intrathymically, and are primed in the periphery. Recall lipid-specific T-cell responses are observed after microbial infections. Lipid-specific T cells release either T helper 1 (TH1)- or TH2-type cytokines, and might have regulatory functions. They therefore participate in immune responses with the same qualification as peptide-specific T cells. The response to lipid antigens is associated with previous or ongoing bacterial infections, the recognition of tumour cells and the control of autoimmunity.