A DR17-restricted T cell epitope from a secreted Mycobacterium tuberculosis antigen only binds to DR17 molecules at neutral pH.
The assembly of peptide-major histocompatability class II complexes in vitro is accelerated at low pH, comparable to that found in the intracellular compartments of metabolically active antigen-presenting cells (APC). Mycobacteria such as Mycobacterium tuberculosis reside in phagosomes with only mildly acidic pH. Therefore, we investigated the pH dependency of peptide-HLA-DR binding for several T cell epitopes of mycobacterial proteins, focussing particularly on well-defined, immunodominant HLA-DR17(3)-restricted T cell epitopes: peptide (p) 3-13 from the cytoplasmic 65-kDa heat shock protein of M. tuberculosis/M. leprae, and peptide 56-65 from the secreted 30/31-kDa protein from M. tuberculosis/M. leprae. p3-13 bound to purified, cell-free DR17 under both acidic and neutral conditions. Four other, unrelated DR17-binding peptides showed the same pH-dependent binding characteristics as p3-13. p56-65, however, only bound to purified DR17 at pH 7 but not at all at pH 4.5. These DR17 peptide binding data were confirmed in cell-bound DR17, in T cell stimulation assays in which fixed APC were peptide-pulsed at acidic or neutral pH before addition of peptide-specific DR17-restricted T cells. As far as we are aware, p56-65 is the only human T cell epitope binding to HLA exclusively at neutral pH. The binding characteristics of p56-65 may reflect dominant processing in alternative, less acidic vacuolar compartments specifically related to the generation of epitopes from (secreted) mycobacterial proteins. The observation that p56-65 is an immunodominant epitope for anti-mycobacterial T cells suggests the relevance of such novel processing compartments in T cell-mediated immunity.
Geluk
A
A
Department of Immunohematology, Blood Bank, University Hospital Leiden, The Netherlands.
van Meijgaarden
K E
KE
de Vries
R R
RR
Sette
A
A
Ottenhoff
T H
TH
D000595:Amino Acid Sequence; D017951:Antigen Presentation / Q000187:drug effects; D000938:Antigen-Presenting Cells / Q000187:drug effects / Q000378:metabolism; D000942:Antigens, Bacterial / Q000378:metabolism*; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D003470:Culture Media / Q000378:metabolism / Q000494:pharmacology; D000939:Epitopes / Q000378:metabolism*; D006684:HLA-DR Antigens / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology
D000942:Antigens, Bacterial; D003470:Culture Media; D000939:Epitopes; D006684:HLA-DR Antigens; D010455:Peptides; D002738:Chloroquine