Glycopeptides bind MHC molecules and elicit specific T cell responses.
Carbohydrates are T cell independent antigens because they do not bind to MHC molecules. However, glycopeptides might potentially bind to MHC molecules via their peptide component for presentation to T cells. We have conjugated the disaccharide galabiose [Gal alpha (1-4)Gal beta] to the amino terminus of a T cell peptide determinant from hen egg-white lysozyme [HEL(52-61)]. The resulting glycopeptide (Gal2-52-61) and a nonglycosylated analogue containing tyrosine and glutamic acid at the amino-terminus (YE-52-61) bound equally well to purified I-Ak. T cell hybridomas were produced after immunization with Gal2-52-61. Many of the T cell hybridomas were glycopeptide-specific and responded to Gal2-52-61 but not to nonglycosylated synthetic peptides or to HEL presented by APC, indicating that the carbohydrate moiety influenced T cell recognition. Recognition was lost with the amino terminal attachment of the disaccharide to a peptide six amino acids longer at the amino terminus than HEL(52-61). Recognition also was lost with peptides containing only a single galactosyl residue or with galabiose bound to a different I-Ak binding peptide. T cells directed to Gal2-52-61 recognized glycopeptides having significant variation in the disaccharide structure, such as HEL(52-61) glycopeptides carrying lactose, cellobiose, or hepta-o-acetylated galabiose. Peptide residues were important features of the T cell epitope; Ala substitutions of two critical T cell contact residues of HEL(52-61) (Tyr53 and Leu56) abrogated T cell reactivity to the glycopeptides without affecting binding to I-Ak. In conclusion, we propose that these T cells recognize a peptide conformation specific to glycopeptide-I-Ak complexes and that this recognition does not involve specific interaction between the carbohydrate moiety and the T cell receptor.
Harding
C V
CV
Washington University School of Medicine, Department of Pathology, St. Louis, MO 63110.
Kihlberg
J
J
Elofsson
M
M
Magnusson
G
G
Unanue
E R
ER
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D006020:Glycopeptides / Q000276:immunology* / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D051379:Mice; D008808:Mice, Inbred CBA; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000276:immunology*
D006020:Glycopeptides; D000949:Histocompatibility Antigens Class II