Cd1b-Mediated T Cell Recognition of a Glycolipid Antigen Generated from Mycobacterial Lipid and Host Carbohydrate during Infection

Abstract

T cells recognize microbial glycolipids presented by CD1 proteins, but there is no information regarding the generation of natural glycolipid antigens within infected tissues. Therefore, we determined the molecular basis of CD1b-restricted T cell recognition of mycobacterial glycosylated mycolates, including those produced during tissue infection in vivo. Transfection of the T cell receptor (TCR) α and β chains from a glucose monomycolate (GMM)-specific T cell line reconstituted GMM recognition in TCR-deficient T lymphoblastoma cells. This TCR-mediated response was highly specific for natural mycobacterial glucose-6-O-(2R, 3R) monomycolate, including the precise structure of the glucose moiety, the stereochemistry of the mycolate lipid, and the linkage between the carbohydrate and the lipid. Mycobacterial production 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 indicate that mycobacteria synthesized antigenic GMM by coupling mycobacterial mycolates to host-derived glucose. Specific T cell recognition of an epitope formed by interaction of host and pathogen biosynthetic pathways provides a mechanism for immune response to those pathogenic mycobacteria that have productively infected tissues, as distinguished from ubiquitous, but innocuous, environmental mycobacteria.

Towards understanding the functional diversity of cell wall mycolic acids of Mycobacterium tuberculosis

“…T-cell recognition is highly specific for the precise structure of natural GMM including the glucose, the linkage of the glucose to the mycolate and the R,Rstereochemistry of the hydroxyl acid part of the mycolate [57]. Upon infection mycobacteria begin to produce GMM which provides a good indicator of local invasion.…”

CD8+ T Cells Accumulate in the Lungs of Mycobacterium tuberculosis-Infected Kb−/−Db−/− Mice, But Provide Minimal Protection

“…The possible role of MHC class Ib-restricted CD8 ϩ T cells during chronic bacterial infection, such as tuberculosis, is not known. In recently infected humans, Lewinsohn et al (20,21) showed that the vast majority of Mtb-reactive, CD8 ϩ T cells in the peripheral blood are restricted by the MHC class Ib molecule, HLA-E. CD1-restricted CD8 ϩ T cells have also been isolated from peripheral blood of infected individuals (22)(23)(24). In mice, Mtbreactive CD8 ϩ T cells restricted by the MHC class Ib molecule, H2-M3, have been identified (25) (26).…”

Mycobacterium tuberculosisRegulates CD1 Antigen Presentation Pathways through TLR-2

“…Human monocytes were isolated from peripheral blood using Ficoll and adherence to tissue-culture flasks and were cultured in RPMI 1640 medium with 10% FBS (33). In selected experiments, monocytes were further depleted of residual lymphocytes using anti-CD20 (L26), anti-CD3 (TCS3), anti-CD56 (B159), and goat anti-mouse Ig-coated magnetic beads (Dynal) such that lymphocytes constituted Ͻ2% of total cells as determined by flow cytometric staining with non-cross-reactive lymphocyte markers.…”