Showing papers by "Clemencia Pinilla published in 2000"

Minimal peptide length requirements for CD4+ T cell clones - implications for molecular mimicry and T cell survival

Abstract: CD4 T lymphocytes usually recognize peptides of 12–16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4 T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4 TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4 TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4 HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.

Contribution of Individual Amino Acids Within MHC Molecule or Antigenic Peptide to TCR Ligand Potency

Abstract: The TCR recognition of peptides bound to MHC class II molecules is highly flexible in some T cells. Although progress has been made in understanding the interactions within the trimolecular complex, to what extent the individual components and their amino acid composition contribute to ligand recognition by individual T cells is not completely understood. We investigated how single amino acid residues influence Ag recognition of T cells by combining several experimental approaches. We defined TCR motifs for CD4+ T cells using peptide synthetic combinatorial libraries in the positional scanning format (PS-SCL) and single amino acid-modified peptide analogues. The similarity of the TCR motifs defined by both methods and the identification of stimulatory antigenic peptides by the PS-SCL approach argue for a contribution of each amino acid residue to the overall potency of the antigenic peptide ligand. In some instances, however, motifs are formed by adjacent amino acids, and their combined influence is superimposed on the overall contribution of each amino acid within the peptide epitope. In contrast to the flexibility of the TCR to interact with different peptides, recognition was very sensitive toward modifications of the MHC-restriction element. Exchanges of just one amino acid of the MHC molecule drastically reduced the number of peptides recognized. The results indicate that a specific MHC molecule not only selects certain peptides, but also is crucial for setting an affinity threshold for TCR recognition, which determines the flexibility in peptide recognition for a given TCR.

Peptide Mimicry of Streptococcal Group A Carbohydrate

Abstract: This chapter explores the immunochemical relationships, as defined by antibodies, between the cell wall polysaccharide of Streptococcus pyogenes (group A streptococci) and peptides. It provides basic information on the structure and immunobiology of the streptococcal cell wall polysaccharide (group A carbohydrate [GAC]). Following comments on the nature of molecular mimicry in general, an overview of prior studies on the cross-reactions between GAC and epitopes on host structures is provided. The next two sections review studies of antibody cross-reactivity between GAC and peptides either that correspond in amino acid sequence to host proteins or that are derived from combinatorial peptide libraries. Molecular analysis of human monoclonal antibodies cross-reactive with N-acetyl-β-D-glucosamine (GlcNAc) and peptides revealed that they used a variety of variable-region genes and exhibited little evidence of antigen-driven somatic mutations. It remains unknown if GlcNAc-specific antibodies are pathogenic and, if so, what structural features predispose the antibodies to pathogenicity. Researchers used the phage-display approach to investigate peptide mimicry of GAC with respect to five GAC-specific monoclonal antibodies, including the murine monoclonal antibody HGAC 39.G3. This antibody (IgG3, kappa chain) was generated with the group A vaccine (GAV; heat-killed, pepsin-treated S. pyogenes) as the immunogen and has specificity for the GlcNAc residues of group A carbohydrate.