Role of single amino acids in the recognition of a T cell epitope.
T cell epitopes can be defined by the use of synthetic peptides, which when added to APC efficiently mimic naturally processed Ag. Free peptide is thought to bind to cell-surface MHC glycoproteins and the TCR then recognizes the resulting complex. The specificity of a tetanus toxin-specific human Th cell clone was investigated using a complete replacement set of peptides in which every amino acid within the minimal T cell epitope was replaced by each of the 19 alternative genetically coded amino acids. Within the minimal epitope, found to be YSYFPSVI (tetanus toxin 593-600), a small number of substitutions could be made without significant loss of activity, defined as substitutions giving peptides whose activity fell within +/- 3 SD of the mean parent response. Y593 could be substituted with F, W, M, L, V, and I; S594 with G and T; Y595, F596, and P597 with no other amino acids; S598 with A; V599 with S, and I600 with L. Rank ordering of the substitutions allowed a precise description to be made of MHC and/or TCR interaction with each amino acid side chain within the epitope. Simplified theoretic calculations based on this study indicate that class II T cell recognition has a specificity greater than 1 in 10(8). Competition experiments indicate that Y595, F596, P597, and I600 are critical for binding of this epitope to its restricting element, HLA DR4Dw14.
Suhrbier
A
A
Queensland Institute of Medical Research, Brisbane, Australia.
Rodda
S J
SJ
Ho
P C
PC
Csurhes
P
P
Dunckley
H
H
Saul
A
A
Geysen
H M
HM
Rzepczyk
C M
CM
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D000939:Epitopes / Q000737:chemistry*; D006684:HLA-DR Antigens / Q000032:analysis*; D006801:Humans; D008969:Molecular Sequence Data; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013329:Structure-Activity Relationship
D000939:Epitopes; D006684:HLA-DR Antigens; D011948:Receptors, Antigen, T-Cell