Showing papers by "Per A. Peterson published in 1995"

A viral inhibitor of peptide transporters for antigen presentation

Abstract: Cytotoxic T lymphocytes lyse target cells after T-cell-receptor-mediated recognition of class I major histocompatibility complex molecules presenting peptides Antigenic peptides are generated in the cytoplasm by proteasomes and translocated into the lumen of the endoplasmic reticulum (ER) by peptide transporters (TAP) Herpes simplex virus (HSV) expresses a cytoplasmic protein, ICP47, which seems to interfere with such immune surveillance by mediating retention of 'empty' class I molecules in the ER By expressing ICP47 in HeLa cells under an inducible promoter, we show that ICP47 efficiently inhibits peptide transport across the ER membrane such that nascent class I molecules fail to acquire antigenic peptides This inhibition was overcome by transfecting murine TAP Further, we demonstrate that ICP47 colocalizes and physically associates with TAP within the cell Inhibition of peptide translocation by a viral protein indicates a previously undocumented potential mechanism for viral immune evasion

Peptide binding and presentation by mouse CD1

Abstract: CD1 molecules are distantly related to the major histocompatibility complex (MHC) class I proteins. They are of unknown function. Screening random peptide phage display libraries with soluble empty mouse CD1 (mCD1) identified a peptide binding motif. It consists of three anchor positions occupied by aromatic or bulky hydrophobic amino acids. Equilibrium binding studies demonstrated that mCD1 binds peptides containing the appropriate motif with relatively high affinity. However, in contrast to classical MHC class I molecules, strong binding to mCD1 required relatively long peptides. Peptide-specific, mCD1-restricted T cell responses can be raised, which suggests that the findings are of immunological significance.

Crystal structure of an H-2Kb-ovalbumin peptide complex reveals the interplay of primary and secondary anchor positions in the major histocompatibility complex binding groove.

Abstract: Sequence analysis of peptides naturally presented by major histocompatibility complex (MHC) class I molecules has revealed allele-specific motifs in which the peptide length and the residues observed at certain positions are restricted. Nevertheless, peptides containing the standard motif often fail to bind with high affinity or form physiologically stable complexes. Here we present the crystal structure of a well-characterized antigenic peptide from ovalbumin [OVA-8, ovalbumin-(257-264), SIINFEKL] in complex with the murine MHC class I H-2Kb molecule at 2.5-A resolution. Hydrophobic peptide residues Ile-P2 and Phe-P5 are packed closely together into binding pockets B and C, suggesting that the interplay of peptide anchor (P5) and secondary anchor (P2) residues can couple the preferred sequences at these positions. Comparison with the crystal structures of H-2Kb in complex with peptides VSV-8 (RGYVYQGL) and SEV-9 (FAPGNYPAL), where a Tyr residue is used as the C pocket anchor, reveals that the conserved water molecule that binds into the B pocket and mediates hydrogen bonding from the buried anchor hydroxyl group could not be likewise positioned if the P2 side chain were of significant size. Based on this structural evidence, H-2Kb has at least two submotifs: one with Tyr at P5 (or P6 for nonamer peptides) and a small residue at P2 (i.e., Ala or Gly) and another with Phe at P5 and a medium-sized hydrophobic residue at P2 (i.e., Ile). Deciphering of these secondary submotifs from both crystallographic and immunological studies of MHC peptide binding should increase the accuracy of T-cell epitope prediction.

Phagocyte-induced antigen-specific activation of unprimed CD8+ T cells in vitro.

Abstract: The strict segregation of the major histocompatibility complex (MHC) class I and class II loading pathways has been challenged by recent reports indicating that MHC class I molecules can acquire antigen in the phagocytic pathway. We now show that this alternative peptide loading pathway can be used efficiently to generate macrophages able to activate unprimed antigen-specific cytotoxic T cells in vitro. Short peptides (8-11 residues), administered in the phagocytic pathway at nanomolar concentrations, were found to be effective in specifically activating naive cytotoxic T lymphocytes (CTL) in vitro, but longer peptides or whole protein antigen were not. Whole protein antigen coated on beads did, however, render macrophages susceptible to lysis by an antigen-specific CTL clone. This indicates that proteolysis in the phagocytic pathway has limited capability for class I-restricted presentation. We propose a model for class I loading in the phagocytic pathway consisting of direct trafficking of nascent MHC class I from the trans-Golgi network to the phagosome, prior to appearance at the cell surface, and the use of the narrow cavity between bead and phagosomal membrane as a peptide exchange/loading compartment. Targeting immunogenic class I-binding peptide to the phagocytic pathway of macrophages facilitates presentation in association with class I. This is a useful tool for CTL response induction in vitro.

Human CD8 transgene regulation of HLA recognition by murine T cells.

Abstract: A series of human CD8 transgenic (hCD8 Tg) mice with differential expression in the thymus and periphery were produced to investigate CD8 coreceptor regulation of repertoire selection and T cell responses. Expression of hCD8 markedly enhanced responses to both HLA class I molecules and hybrid A2/Kb molecules providing functional evidence for a second interaction site, outside of the alpha 3 domain, which is essential for optimal coreceptor function. Peripheral T cell expression of hCD8 was sufficient to augment responsiveness to HLA class I, as hCD8 Tg mice which lacked thymic expression responded as well as mice expressing hCD8 in the thymus and periphery. Both murine CD8+ and CD4+ T cells expressing hCD8 transgenes exhibited markedly enhanced responses to foreign HLA class I, revealing the ability of T cell receptor repertoires selected on either murine class I or class II to recognize human class I major histocompatibility complex (MHC). In contrast to recognition of foreign class I, thymic expression of hCD8 transgenes was absolutely required to enhance recognition of antigenic peptide restricted by self-HLA class I. Thus, our studies revealed disparate requirements for CD8 coreceptor expression in the thymus for selection of a T cell repertoire responsive to foreign MHC and to antigenic peptides bound to self-MHC, providing a novel demonstration of positive selection that is dependent on human CD8.

Antigen‐presenting Function of the TL Antigen and Mouse CD1 Molecules

Abstract: The hallmark of all the nonclassical antigen-presenting molecules, including nonclassical class I and nonclassical class II (Karlsson et al. 1992) molecules, is their lack of polymorphism. It is presumed, therefore, that these nonclassical molecules must have a distinct antigen-presenting function in which polymorphism is not advantageous. In some cases this may involve presentation of a nonpeptide antigen, as has been demonstrated for human CDlb. It is possible that a molecule adapted to present bacterial lipids would remain relatively nonpolymorphic, because a lipid, which is the end product of a complex biosynthetic pathway, is likely to evolve less rapidly than a short stretch of amino acid sequence containing a T-cell epitope. Alternatively, the lack of polymorphism could reflect the presentation by these molecules of relatively invariant peptides, such as those derived from heat shock proteins. It also is possible that a nonpolymorphic molecule could be selected for the presentation of modified peptides. An example of this is the M3 molecule, which can bind even short peptides as long as they have a formylated N-terminus (Fischer Lindahl et al. 1991). Based upon their structural differences, we believe it is likely that the TL antigen and mCD1 are likely to present different types of ligands. The presence in the TL antigen of the conserved amino acids, which in class I normally form hydrogen bonds with peptides, suggests that the TL antigen also can present nanomeric peptides. A peptide antigen-presenting function also is suggested by the expression of the TL antigen by at least one antigen-presenting cell type, the epithelial cell of the intestine, and by the ability of alloreactive T cells to recognize the TL molecule. While we favor the hypothesis that the TL antigen presents peptides, the data cited above do not constitute formal proof of any kind of antigen-presenting function, and it remains possible that the TL antigen does something else. As noted above, no attempts to elucidate the structure of the ligands bound to the TL antigen have so far succeeded, including the screening of bacteriophage display libraries (Castano, A.R., Miller, J.E., Holcombe, H.R., unpublished data). In contrast, our recent work has demonstrated that mCD1 presents relatively long peptides with a structural motif distinct from classical class I molecules. This mCD1-binding motif, which is present in a wide range of proteins, does not by itself provide a simple explanation for the lack of mCD1 polymorphism and, as noted above, it remains possible that the natural ligand for mCD1 is a nonpeptide structure. Besides their lack of polymorphism, the TL antigen and mCD1 molecules share two additional features in common which might give insight into their biological role. First, their surface expression does not depend upon the presence of a functional TAP transporter, and they probably can reach the cell surface as empty molecules. Second, both molecules are expressed by epithelial cells in the intestine. This leads to the speculation that these two nonclassical class I molecules could be involved in sampling or uptake of lumenal peptides for their ultimate presentation to cells of the systemic immune system. For example, longer lumenal peptides could be taken up by mCD1, and perhaps by the TL antigen, and then further processed to nonamers for presentation by classical class I molecules. They also could be transported across the epithelial cell by the TL antigen or mCD1 and subsequently presented by either class I or class II molecules expressed by cells in the lamina propria. This sampling or uptake mediated by either the TL antigen or mCDl could play a role in the induction of immune responses, or more likely perhaps, in the induction of systemic oral tolerance to peptide antigens. Alternatively the TL antigen and mCDI might be more directly involved in antigen presentation to resident lymphocytes in the intestinal mucosa. More than 75% of the