Lymphocyte Specificity to Protein Antigens. IV. In Vivo and In Vitro Activation of Cytochrome-Specific T Cells Is Dependent on Protein Conformation*

The immune response to cytochrome c in BALB/c mice is delayed due to inability of their non-specific antigen-presenting cells to provide its immunodominant epitope

The antibody response to horse cytochrome c (cyt.c) in BALB/c mice developed slowly and a substantial production of IgG antibodies was observed only 26-30 days after immunization. Lymph node cells (LNC) of unimmunized mice proliferated weakly in response to both native cyt.c and its synthetic peptides. On day 8 after immunization, LNC could not be stimulated with native cyt.c and peptide 92-104. However, they did proliferate in response to cyt.c peptides 1-6, 1-13, 2-13, 14-22, 46-56, 57-77, 61-77 and 61-69 which are closely related in horse and mouse cyt.c. On day 26, both native cyt.c and the peptides, including 92-104, were equally active in stimulating LNC proliferation. Both plastic-adherent and cyt.c-specific cells panned from day 8 cells enhanced the response of unprimed cells to native cyt.c. Elimination of B cells demonstrated that primary recognition of cyt.c was mediated, at least partly, by non-specific antigen-presenting cells (APC) while later B cells of additional specificities were involved. It is concluded that immunization with horse cyt.c initiated an autoimmune response resulting in T-dependent anergy. Peptide determinants processed by non-specific APC stimulated corresponding autoreactive T cells. Specific B cells which appeared as a result of the response maturation processed successfully the immunodominant epitope and finally mediated proliferative and antibody responses.

Lymphocyte specificity to protein antigens. V. Conformational dependence of activation of cytochrome c-specific T cells

Variations in the immunogenic and antigenic properties of native and denatured forms of cytochrome c were observed depending on the strain of mouse tested. In C57BL/6 and (C57BL/6 X DBA/2)F1 (BDF1) mice, priming with either native or denatured cytochrome c (apocytochrome c) gave rise to T cell blasts responding in a similar fashion to the two forms of the antigen and to different peptides derived from CNBr cleavage of the protein when tested for proliferation in the presence of C57BL/6 or BDF1 accessory cells. A different pattern of proliferation was observed when apocytochrome c-specific DBA/2 or BDF1 T cell blasts were tested with DBA/2 accessory cells. In this case, no response was obtained to heme peptide 1-65. This was not due to an inability of DBA/2 macrophages to process and present heme peptide 1-65, as they were able to present this antigen to native cytochrome c-specific BDF1 T cell blasts. Thus, it seems that different sets of clones are generated upon priming BDF1 mice with denatured cytochrome c which are able to recognize different sets of peptides depending on the nature of the accessory cells. The results obtained are consistent with the hypothesis that degradation and presentation of native and denatured cytochrome c by macrophages is dependent on the three-dimensional conformation of the protein.