Robert G. Urban

Analysis of MHC-presented peptides: applications in autoimmunity and vaccine development

T cells recognize antigenic peptides presented on the cell surface by major histocompatibility complex (MHC) molecules. Here, Roman Chicz and Robert Urban describe the features of peptides bound to MHC molecules and the mechanism by which these surface proteins bind diverse peptide ligands with high affinity. In addition, they discuss the application of new technologies to the identification of MHC-associated peptides.

Purification of the STB enterotoxin of Escherichia coli and the role of selected amino acids on its secretion, stability and toxicity

The methanol-insoluble heat-stable enterotoxin of Escherichia coli (STB) was purified and characterized by automated Edman degradation and tryptic peptide analysis. The amino-terminal residue, Ser-24, confirmed that the first 23 amino acids inferred from the gene sequence were removed during translocation through the E. coli inner membrane. Tryptic peptide analysis coupled with automated Edman degradation revealed that disulphide bonds are formed between residues Cys-33 and Cys-71 and between Cys-44 and Cys-59. Oligonucleotide-directed mutagenesis performed on the STB gene demonstrated that disulphide bond formation does not precede translocation of the polypeptide through the inner membrane and that disulphide bridge formation is a periplasmic event; apparently, elimination of either of two disulphides of STB renders the molecule susceptible to periplasmic proteolysis. In addition, a loop defined by the Cys-44-Cys-59 bond contains at least two amino acids (Arg-52 and Asp-53) required for STB toxic activity.

Direct binding of the Mtv7 superantigen (Mls-1) to soluble MHC class II molecules

The superantigen encoded by the mouse mammary tumor virus (MMTV) is a potent stimulator of T cells when bound to MHC class II molecules. Recent data from this laboratory have shown that the Mtv7 superantigen, Mls-1, elicits a strong T cell response when presented by HLA-DR. To expand these observations further, we have produced the 28 kDa extracellular domain and the 18 kDa carboxy-terminal subfragment of the Mls-1 protein in E. coli and studied their interaction with human MHC class II molecules in vitro. In this report, we demonstrate direct binding of these recombinant forms of the Mls-1 protein to soluble HLA-DR1 and HLA-DR4, but not to HLA-A2. Our data imply a unique class II interaction site of retroviral superantigens that is not shared with bacterial superantigens.

MHC molecules : expression, assembly, and function

1. Major Histocompatibility Antigens: An Introduction.- 2. The Major Histocompatibility Complex Genes and Their Transcriptional Regulation.- The Murine Major Histocompatibility Complex.- The Major Histocompatibility Complex of Humans, the HLA.- Developmental and Tissue-Specific Expression of MHC Genes.- Role of Aberrant Expression of MHC Gene Products in Immunologic Disease.- Cis-Elements and Transcription Factors That Control MHC Class I Gene Expression.- Factors and Elements That Control MHC Class II Gene Expression.- Models of Activation and Repression.- Concluding Comments.- 3. TAP Peptide Transporters and Antigen Presentation.- Evidence for Peptide Translocation by TAP.- Tap Genes and Sequences.- TAP as Member of the ABC Transporter Family.- Structure and Assembly of the TAP Complex.- In Vitro Assays for Peptide Binding and Transport by TAP.- Sequence Specificity of Peptide Transport by Different TAP Molecules.- Relating Specificity to the Structure of Polymorphic TAP Molecules.- Length of Transported Peptides.- TAP-Dependent and Independent Presentation.- TAP and Disease.- Concluding Remarks.- 4. Molecular Chaperones in MHC Class I and Class II Biosynthesis and Assembly.- Introduction: ER Resident Molecular Chaperones.- Molecular Chaperones Implicated in Class I Biosynthesis and Assembly.- Molecular Chaperones Implicated in MHC Class II Biosynthesis and Assembly.- Quality Control of MHC Molecules Mediated by Molecular Chaperones.- 5. Polypeptide Release from Lysosomes.- Synthesis and Transport of Lysosomal Hydrolases.- Entry of Degradation Substrates.- Lysosomal Hydrolysis.- Polypeptide Release from Lysosomes.- Possible Immunological Relevance.- Conclusion.- 6. Intracellular Trafficking of MHC Class II Molecules.- Assembly of MHC Class II Molecules in the ER and Early Stages of Transport.- Processing Intermediates of Invariant Chain.- Post-Golgi Trafficking of MHC Class II Molecules and Sites of Invariant Chain Degradation.- Intracellular Sites of Assembly of Peptide:MHC Class II Complexes.- 7. The Role of HLA-DM in Class II Antigen Presentation.- DM Sequence and Structure.- Regulation of Expression.- Genomic Organization of DM Genes.- Evolutionary Considerations.- DM Polymorphism.- Analysis of DM Mutant Cells.- The Mechanism of DM Action.- The Biology of Antigen Processing.- The Biosynthesis and Maturation of Class II.- Conclusion.- 8. Crystallographic Analysis of Peptide Binding by Class I and Class II Major Histocompatibility Antigens.- Class I Major Histocompatibility Antigens.- Class II Major Histocompatibility Antigens.- Similarities and Differences Between Class I and Class II Major Histocompatibility Antigens.- 9. HLA and Disease: Molecular Basis.- Tissue Typing Techniques.- Epidemiological Analysis.- Paradigms of Diseases Associated with the MHC.- HLA-B27 and Ankylosing Spondylitis.- MHC II and Disease.- Concluding Remarks.- 10. Epitope Prediction Algorithms for Class I MHC Molecules.- Elucidation of Peptide-Binding Motifs.- Anchor Residues.- Peptide-Binding Assays.- Physical Basis for Peptide-Binding Motifs.- Prediction of Binding Peptides.- Exceptional Peptides.- Peptide Binding and Antigenicity.- Conclusions.- 11. Options for TCR Interactions: TCR Agonists, Antagonists and Partial Agonists.- Introduction: Smart and Dumb T Cell Receptors.- Full Agonists, Partial Agonists and Antagonists.- What Do TCR Partial Agonists and Antagonists Do?.- T Cell Development.- The Direction of Mature T Cell Responses.- The Two Edged Sword: Antagonists as Protectors and Perpetrators of Disease.- How Do Antagonist/Partial Agonists Work?.- Concluding Remarks.- 12. Role of Ligand Density in T Cell Reactions.- Background.- The Study of Peptides Recognized by CD8+ CTL.- What Determines the Efficacy of CTL-Mediated Target Cell Lysis?.- Role of Ligand Density.- Concluding Remarks.- 13. Cooperative Recognition of MHC Class II Molecules:Peptide Complexes by the T Cell Receptor and CD4.- TCR Recognition of MHC Class II:Peptide Complexes.- CD4 Binding to MHC Class II Molecules.- CD4 Interaction With the TCR:CD3 Complex.- Conclusions.- 14. Receptors for MHC Class I Molecules in Human Natural Killer Cells.- MHC Class I Molecules Inhibit NK Cell Cytotoxicity.- Murine NK Inhibitory Receptors.- Human NK Inhibitory Receptors.- A New Family of Immunoglobulin-Superfamily (Ig-SF) Genes Selectively Expressed in Human NK Cells.- Evidence That NK-Specific Ig-SF Genes May Encode Human Receptors for Class I Molecules.- NK Recognition of MHC Class I Molecules Is Mediated by a Complex System.- 15. The MHC in Host-Pathogen Evolution.- Selection Acting on the Human Host.- Pathogen Avoidance of T Cell Recognition.- Mechanisms of Decreasing Antigen Presentation.- Mechanisms of Avoiding T Cell Recognition of Specific Epitopes.- Perspective.- 16. Peptide-Mediated Regulation of Allergic Diseases.- The Role of CD4+ T Cell Subsets.- The Immunological Objectives of Allergy Therapy.- Regulation of Specific T Cells by Peptides.- Deviation of Thl/Th2 Phenotype of the Responder Population.- 17. Genetic Modulation of Antigen Presentation.- Vaccines.- Genetic Immunization for Viral Diseases.- Treatment of Autoimmune Disease.- Conclusion.

MAJOR HISTOCOMPATIBILITY ANTIGENS: AN INTRODUCTION

Specific immunity depends on the gene products encoded within the major histocompatibility complex (MHC). As the name suggests, the MHC was first identified as a group of genetic loci which influenced the type of immunological responses which followed tissue transplantation. Over 20 years ago, the involvement of MHC molecules in the interaction between B and T cells was demonstrated to be specific and restricted.1–3 As it turns out, the products of two families of MHC encoded genes, termed class I and class II, are the primary molecules used by the immune system to educate immune cells (not to recognize self) and subsequently to activate the entire system following recognition of foreign matter. MHC class I and class II molecules are highly polymorphic membrane expressed proteins which function by binding peptides and “presenting” them to T cells. The last two decades have witnessed a wealth of discovery on MHC molecules and antigen presentation in general, yet more and more detail continues to be uncovered. This chapter is intended to review some of the hallmark observations made in the last five years and to prepare those newly interested in immunology for the more detailed chapters that follow.