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Publié par | humboldt-universitat_zu_berlin |
Publié le | 01 janvier 2009 |
Nombre de lectures | 37 |
Langue | English |
Poids de l'ouvrage | 3 Mo |
Extrait
Identification and characterization of peptide-like MHC-
ligand exchange catalyst as immune response
enhancer
Dissertation
zur Erlangung des akademischen Grades
doctor rerum naturalium
(Dr. rer. nat.)
im Fach Biologie
eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät I
der Humboldt-Universität zu Berlin
Von
M.Pharm, Shashank Gupta
(20.07.1978, Lucknow, India)
Präsident der Humboldt-Universität zu Berlin
Prof. Dr. Christoph Markschies
Dekan der Mathematisch-Naturwissenschaftlichen Fakultät I
Prof. Dr. Lutz-Helmut Schön
Gutachter:
Prof. Dr. Richard Lucius
Prof. Dr. Alf Hamann
PD. Dr. Christian Freund
Tag der mündlichen Prüfung: 14. 04. 2009
iContent
IDENTIFICATION AND CHARACTERIZATION OF PEPTIDELIKE MHCLIGAND
EXCHANGE CATALYST AS IMMUNE RESPONSE ENHANCER I
CONTENT II
SUMMARY V
ZUSAMMENFASSUNG VI
1 INTRODUCTION 1
1.1 The role of CD4+ T cells in antigen recognition and immune surveillance 1
1.1.1 Activation of CD4+ T cells 1
1.1.2 Signalling in T cell activation 2
1.2 Major histocompatibility complex (MHC) 3
1.2.1 Genome organisation of MHC proteins 3
1.2.2 MHC class I structure and antigen processing 4
1.2.3 MHC class II structure 5
1.2.4 MHC class II: synthesis and antigen processing pathways 6
1.2.4.1 Endosomal pathway 6
1.2.4.2 Cell surface loading 7
1.2.5 Peptide binding and stabilization 9
1.3 Conformational transitions in MHC class II proteins 10
1.3.1 Receptive and non‐receptive MHC conformation states 11
1.4 Mediators of the MHC class II conformation transition 12
1.4.1 HLA‐DM 12
1.4.2 ‘ MHC loading enhancer’ (MLE) compounds 13
1.5 Environmental factors and autoimmune disorders 15
1.6 MHC linkage to various diseases 16
1.7 Celiac disease 17
1.7.1 Factors causing celiac disease 17
1.7.2 Gluten antigen and HLA‐DQ mediated presentation 17
2 OBJECTIVES 21
3 MATERIALS AND METHODS 22
3.1 Chemicals and Solutions 22
3.2 Antibodies 22
3.3 Peptides 23
3.4 Peptide‐MLE 23
ii 3.5 Soluble MHC class II molecules 23
3.6 Cells 24
3.7 Buffers 24
3.8 Instruments 25
3.9 Softwares 25
3.10 Enzyme‐Linked Immunosorbant Assay (ELISA) 26
3.11 Labelling of HLA‐DR molecules with biotin 26
3.12 ELISpot assay 26
3.13 Confocal laser scanning microscopy 27
3.14 Fluorescence activated cell sorting (FACS) 27
3.15 Cell culture 28
3.15.1 Maintainence of antigen presenting cells (APC) 28
3.15.2 of T cells 28
3.15.3 Isolation and in vitro maturation of dendritic cells (DC) 28
3.16 CTLL assay 29
33.17 [H ] thymidine assay 29
3.18 Peptide loading of soluble MHC molecules 29
3.18.1 Loading of ‘empty’ HLA‐DR molecules 29
3.18.2 Peptide loading of ‘empty’ HLA‐DQ2 molecules 30
3.19 Ligand‐exchange of soluble HLA‐DR molecules 30
3.20 Calculation of the ‘catalytic rate enhancement’ 30
3.21 Antigen loading of the cell surface MHC molecules 30
3.22 T cell assays 31
3.22.1 Pulse wash 31
3.22.2 Permanent exposure 31
3.23 ANS binding measurements 32
3.24 Intrinsic tryptophan fluorescence measurements 32
3.25 Probing with conformational specific antibodies 32
3.26 MLE effect by conformation specific antibodies 32
4 RESULTS 33
4.1 Anchor side chains of short peptide fragments trigger ligand exchange of class II MHC proteins. 33
4.1.1 Rationally designed short peptides show “MLE” activity 33
4.1.2 Hydrogen bond forming groups enhance MLE activity 35
4.1.3 Dipeptides show ‘drug like’ stereospecificity 36
iii4.1.4 MLE activity always correlates with P1 anchor preferences 37
4.1.5 Peptide‐MLE can trigger reversible ligand exchange 38
4.1.6 Pocket‐1 of HLA‐DR1 as target for peptide‐MLE 39
4.1.7 Summary of catalytic activity of short peptides 41
4.1.8 Peptide‐MLE can enhance antigen loading on living antigen presenting cell (APC) 43
4.1.9 Enhancement of antigen loading on dendritic cells 50
4.1.10 Amplification of the antigen specific CD4+ T cell response in vitro 51
4.1.11 of the antigen CD4+ T cell ex vivo 55
4.2 Characterization of molecular mechanism behind MLE mediated ligand exchange 56
4.2.1 Spectral analysis 56
4.2.1.1 Monitoring of conformational shift by binding of ANS dye 56
4.2.1.2 g of nal shift by intrinsic tryptophan fluorescence 58
4.2.2 Detection of receptive state with conformational specific antibodies 60
4.2.2.1 Conformational specific antibodies targeting the peptide binding site 60
4.2.2.2 l targeting site distant from peptide binding site 63
4.2.2.3 l shift can be detected also in defined ligand free HLA‐DR1 preparation 64
4.2.2.4 MEM antibodies show MLE activity 65
4.3 Role of peptide‐MLE in celiac disease 67
4.3.1 Structure activity relationship of dipeptides on HLA‐DQ2 67
4.3.2 Dipeptides can catalyze loading of gluten derived antigen 69
4.3.3 Enhanced loading of gluten derived antigen by dipeptides on APC cell surface 71
4.3.4 Amplification of gliadin specific CD4+ T cell response by peptide‐MLE 73
5 OUTLOOK 76
5.1 Therapeutic potential of MLE 76
5.2 Structural dynamics of MHC molecules 76
5.3 MLE as putative environmental risk factor or implication on autoimmune induction 76
6 DISCUSSION 77
REFERENCES 84
APPENDIX 103
ABBREVIATIONS 103
ACKNOWLEDGEMENTS 105
EIDESSTATTLICHE ERKLÄERUNG 108
iv Summary
MHC class II molecules present antigenic peptides on the cell surface for the surveillance
by CD4+ T cells. To ensure that these ligands accurately reflect the content of the
intracellular MHC loading compartment, a complex processing pathway has evolved that
delivers only stable peptide/MHC complexes to the surface.