Mapping major and minor T-cell epitopes in vitro and their immunogenic or tolerogenic effect in vivo in non-human primates.
The immunogenicity of synthetic peptides of in vitro mapped T- and B-cell epitopes from a Streptococcus mutans cell-surface antigen were investigated in non-human primates. Peptide (1-15) contains T-cell (7-15) and B-cell (8-13) epitopes, but is only immunogenic if dimerized (1-15)2 or linked to the carrier tetanus toxoid (1-15)TT. Monomers and dimers of T- and B-cell epitopes were prepared and used to immunize macaques. Immunogenicity was assayed in lymphocytes by the uptake of [3H]thymidine and serum antibodies by a solid-phase radioimmunoassay. Macaques immunized with the dimerized (1-15)2 or carrier-linked peptide (1-15)TT exhibited in vitro T-cell proliferative responses to peptides (1-15) and (7-15). T cells from animals immunized with peptides (1-15), (7-15) or (7-15)2 failed to elicit an immune response. In order to establish if these non-immunogenic peptides might induce tolerance, the same macaques were challenged with the immunogenic peptide (1-15)TT. The results suggest that T-cell responses to peptide (1-15) were reestablished, but instead of responding to peptide (7-15) they were stimulated by a hitherto silent epitope (1-7). Tolerance to the major T-cell epitope (7-15) and the expression of a minor (silent) T-cell epitope (1-7) was associated with B-cell tolerance, suggesting that T-cell help for antibodies resides in the major T-cell epitope (7-15). However, short-term T-cell lines revealed T-cell responses to peptides (1-7) and (7-15) in both tolerized and immunized macaques, but the relative frequency of the minor epitope (1-7)-reactive lines was significantly higher in tolerized animals, whilst that for the major epitope (7-15) was higher in immunized animals. These findings suggest that the silent epitope (1-7) is really cryptic, in that it can be detected if the cell lines are first expanded in vitro with the whole peptide (1-15) and then stimulated with the truncated peptides (1-7) or (7-15). The results are consistent with the concept of a hierarchy of major and minor T-cell epitopes, now demonstrated in non-human primates, in which tolerance to the major T-cell epitope is associated with tolerance to antibody formation and the emergence of a minor T-cell epitope.
Walker
P R
PR
Department of Immunology, United Medical School, Guy's Hospital, London, U.K.
Smerdon
R
R
Haron
J
J
Lehner
T
T
D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D002455:Cell Division / Q000276:immunology; D002460:Cell Line; D000939:Epitopes / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000032:analysis; D007108:Immune Tolerance / Q000276:immunology*; D007074:Immunoglobulin G / Q000096:biosynthesis; D008251:Macaca; D013295:Streptococcus mutans / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
D000942:Antigens, Bacterial; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G