Lipoprotein Access to MHC Class I Presentation During Infection of Murine Macrophages with Live Mycobacteria

Abstract

Following uptake by macrophages, live mycobacteria initially reside within an immature phagosome that resists acidification and retains access to recycling endosomes. Glycolipids are exported from the mycobacterial phagosome and become available for immune recognition by CD1-restricted T cells. The aim of this study was to explore the possibility that lipoproteins might similarly escape from the phagosome and act as immune targets in cells infected with live mycobacteria. We have focused on a 19-kDa lipoprotein from Mycobacterium tuberculosis that was previously shown to be recognized by CD8+ T cells. The 19-kDa Ag was found to traffic separately from live mycobacteria within infected macrophages by a pathway that was dependent on acylation of the protein. When expressed as a recombinant protein in rapid-growing mycobacteria, the 19-kDa Ag was able to deliver peptides for recognition by MHC class I-restricted T cells by a TAP-independent mechanism. Entry into the class I pathway was rapid, dependent on acylation, and could be blocked by killing the mycobacteria by heating before infection. Although the pattern of 19-kDa trafficking was similar with different mycobacterial species, preliminary experiments suggest that class I presentation is more efficient during infection with rapid-growing mycobacteria than with the slow-growing bacillus Calmette-Guérin vaccine strain.

Mycobacterial Lipopeptides Elicit CD4+ CTLs in Mycobacterium tuberculosis-Infected Humans

“…There are several alternative mechanisms-besides supporting APC costimulation-for how lipidation of proteins could promote Ag-specific T cell responses: 1) improvement of Ag presentation as reported for synthetically palmitoylated peptides (79 -81) by modulating Ag processing (82) and intracellular trafficking (83,84), as the lipid moiety is required to direct the mycobacterial lipopeptides from the phagosome to the MHC-loading machinery (85). 2) Stabilization of the protein-MHC complex by protrusion of the lipid moiety from the MHC class II-binding groove and attachment to the phospholipid bilayer of the endosomal membrane (86).…”

Role of urothelial cells in BCG immunotherapy for superficial bladder cancer

“…However, only a small fraction of commercially available BCG preparations consists of live BCG. Therefore, most BCG particles will be degraded, and mycobacterial glycoproteins and lipoproteins are transported to the cell surface (Neyrolles et al, 2001).…”

“…New insights support a role for the interaction of (airway)epithelial cells and bacteria in the initiation of the immunological cascade (Levine, 1995;Neyrolles et al, 2001). Bacillus Calmette-Guérin-treated urothelial tumour cells are now considered as active participants in the cytokine-mediated initiation and/or regulation of the early immune response (Alexandroff et al, 1999).…”

“…In untreated bladder cancer patients, a loss or alteration of MHC class I expression is seen in tumour cells (Saint et al, 2001). Bacillus Calmette-Guérin-infected cells present BCG glycoprotein and lipoprotein antigens on their MHC class I molecule (Neyrolles et al, 2001). This may be a trigger for NK cells to attack BCG-infected urothelial tumour cells.…”

Mycobacterium tuberculosis-Specific CD8+ T Cells and Their Role in Immunity

“…DNA vaccination of mice elicited CTL activity against four of the peptides. Two of the peptides (Ag85B [143][144][145][146][147][148][149][150][151][152] and Ag85B [199][200][201][202][203][204][205][206][207] ) were able to stimulate short-term antigenspecific CD8 + T cell lines from BCG-vaccinated individuals. In the case of Ag85B [199][200][201][202][203][204][205][206][207] , tetramers were made and CD8 + T cells that stained with the tetramers were enriched in the short-term cell lines.…”