Epitopes for human CD4+ cells on diphtheria toxin: Structural features of sequence segments forming epitopes recognized by most subjects

Authors

  • Raghavanpillai Raju,

    1. Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, USA
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  • Duraiswamy Navaneetham,

    1. Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, USA
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  • David Okita,

    1. Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, USA
    2. Department of Pharmacology, School of Medicine, University of Minnesota, Minneapolis, USA
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  • Brenda Diethelm-Okita,

    1. Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, USA
    2. Department of Pharmacology, School of Medicine, University of Minnesota, Minneapolis, USA
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  • Daniel McCormick,

    1. Mayo Protein Core, Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, USA
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  • Bianca M. Conti-Fine

    Corresponding author
    1. Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, USA
    2. Department of Pharmacology, School of Medicine, University of Minnesota, Minneapolis, USA
    • Department of Biochemistry, CBS, University of Minnesota, 1479 Gortner Ave., St. Paul, MN 55108, USA (Fax: +1-612-625-5780)
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    • Previously known as Bianca M. Conti-Tronconi.


Abstract

The sequence regions of diphtheria toxin (DTX) recognized by CD4+ T cells of seven healthy humans of different major histocompatibility complex haplotypes were identified. Overlapping synthetic peptides, screening the DTX sequence, were used to test in proliferation assays unselected blood CD4+ cells, or DTX-specific CD4+ lines propagated by stimulation with DTX of blood mononuclear cells. Blood CD4+ cells and DTX-specific CD4+ lines gave consistent results. Although each subject had an individual pattern of peptide recognition, six peptide sequences (residues 271–290, 321–340, 331–350, 351–370, 411–430 and 431–450) were recognized by all subjects. In the native DTX molecule, these sequence regions are flanked by sequence loops exposed on the DTX surface. They overlap uncharged segments of the DTX sequence. These structural properties may be general requirements for immunodominance in CD4+ cell sensitization in humans.

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