| Summary: | Characterization of immunodominant T cell sites has been effectively performed by a number of laboratories (reviewed in 1) using protein sequence variants, cleavage fragments, and synthetic peptides. Some studies (2) have been interpreted as supportive of the possibility of multiple conformations of peptide antigen and/or multiple antigen-binding sites on the la molecule. The possibility that distinct T cell specificities might reflect distinct recognition or views of a single peptide conformation associated with a single la site has received little attention, primarily because little could be inferred about the conformation of the antigenic peptide on the APC in most experimental systems studied. We have previously described an immunodominant site in sperm whale myoglobin in a region encompassing glutamic acid 109, identified using myoglobin sequence variants (3), and have subsequently isolated T cell clones with the same reactivity pattern (4). In this paper we characterize two such clones using a panel of synthetic peptides. The clones showed different response patterns that are found to be totally consistent with a model of the distinct T cell specificities reflecting distinct "views " of an amphipathic a-helical conformation. Thus, when one considers the likely secondary structure of antigen existing in association with the complex structure of the la molecule, distinct T cell recognition specificities need not imply distinct structural forms of antigen or sites ofantigen binding, but rather may reflect distinct views recognized by the T cell receptor. Materials and Methods Mice. B10.D2 and (B10.D2 X B10.BR)F, mice were obtained from The Jackson
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