CD1b-mediated T cell recognition of a glycolipid antigen generated from mycobacterial lipid and host carbohydrate during infection

T cells recognize microbial glycolipids presented by CD1 proteins, but ther e is no information regarding the generation of natural glycolipid antigens within infected tissues. Therefore, we determined the molecular basis of C D1b-restricted T cell recognition of mycobacterial glycosylated mycolates, including those produced during tissue infection in vivo. Transfection of t he T cell receptor (TCR) alpha and beta chains from a glucose monomycolate (GMM)-specife T cell line reconstituted GMM recognition in TCR-deficient T lymphoblastoma cells. This TCR mediated response was highly specific for na tural mycobacterial glucose-6-O-(2R, 3R) monomycolate, including the precis e structure of the glucose moiety, the stereochemistry of the mycolate lipi d, and the linkage between the carbohydrate and the lipid. Mycobacterial pr oduction of antigenic GMM absolutely required a nonmycobacterial source of glucose that could be supplied by adding glucose to media at concentrations found in mammalian tissues or by infecting tissue in vivo. These results i ndicate that mycobacteria synthesized antigenic GMM by coupling mycobacteri al mycolates to host-derived glucose. Specific T cell recognition of an epi tope formed by interaction of host and pathogen biosynthetic pathways provi des a mechanism for immune response to those pathogenic mycobacteria that h ave productively infected tissues, as distinguished from ubiquitous, but in nocuous, environmental mycobacteria.