MAJOR histocompatibility complex (MHC) class I and class II molecules bind immunogenic peptides and present them to lymphocytes bearing the αβ T-cell antigen receptor (TCR)1-4. An analogous antigen-presenting function also has been proposed for the non-MHC-encoded GDI molecules5, a family of non-polymorphic, β2-microglobulin-associated glycoproteins5-8 expressed on most professional antigen-presenting cells9-11. In support of this hypothesis, CD1 molecules are recognized by selected CD4-CD8- αβ or γδ8TCR+ T-cell clones12-14, and we have recently shown that GDI molecules restrict the recognition of foreign microbial antigens by αβTGR+ T cells10. But the substantial structural divergence of GDI from MHC class I and class II molecules7, raises the possibility that the antigens presented by the GDI system may differ fundamentally from those presented by MHC-encoded molecules. Here we report that a purified CDlb-restricted antigen of Mycobacterium tuberculosis presented to αβTCR+ T cells is mycolic acid, a family of α-branched, β-hydroxy, long-chain fatty acids found in mycobacteria15,16. This example of non-protein microbial antigen recognition suggests that αβTCR+ T cells recognize a broader range of antigens than previously appreciated and that at least one member of the GDI family has evolved the ability to present lipid antigens.
ASJC Scopus subject areas