Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Therapeutic gene modulation wikipedia , lookup
Gene expression profiling wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
DNA vaccination wikipedia , lookup
Mir-92 microRNA precursor family wikipedia , lookup
Structure and Function of the Major Histocompatibility Complex (MHC) Encoded Proteins Main topics: • • • • • • Antigen recognition of T cells Structure of ”classical” polymorphic MHC I and MHC II molecules Antigen binding properties of MHC molecules Heterogeneity/polymorphism of MHC molecules (in drafts) Non-classical MHC Ib and MHC-like molecules Other, non-immunological function of MHC Most of T cells recognize protein derived short peptides as antigenic epitopes by the help of the antigen presenting cells Peptides could be produced from almost any part of the proteins. They can overlap with the epitopes recognised by the antibodies, but they can also derive from the cryptic inner side of the proteins. protein T cell epitope B and T cell epitope The peptides recognised by the T cells produced by proteolytic cleavage from antigenic proteins, therefore the T cell epitopes are considered as neoepitopes The difficulty of peptide recognition • Short peptides are hard to recognize because they could not form stabile ordered structure • Other proteins could stabilize the antigen derived peptides in a stretched conformation (CHAPERON FUNCTION) • Molecules encoded in the MHC gene region provide the stabilizing function. MHC encoded molecules are necessary for the peptide recognition of the T cells (review) Two different type of MHC molecules are responsible for the presentation of peptides from two different cellular compartments • Endogenous antigen presenting pathway: - peptides from proteins (generally synthesized by the cell himself), which are localised in the cytosol molecules are encoded in the MHC I gene region MHC I molecules peptides are recognized by cytotoxic CD8+ T cells (e.g. peptides derived from viral proteins synthesized by the infected cell) • Exogenous antigen presenting pathway: - peptides derived from proteins internalized from the extracellular space, and localised in the endosome molecules are encoded in the MHC II gene region MHC II molecules peptides are recognized by helper CD4+ T cells (e.g. peptides derived from antigens engulfed and digested by professional antigen presenting cells) The two antigen presentation pathways differ in several ways (antigen presentation pathways will be discussed on the next lecture in details) The synthesis and the structure of the classical MHC I and MHC II molecules MHC I MHC II GENES: exons: 1 2 3 4 5 67 8 leader, signal n.t. protein domains s α-chain NH - α1 α2 α3 -COOH NH2- -COOH 2 3 4 56 leader, signal tm c 2 β2-microglobulin 1 7 n.t. s α1 α2 s β1 β2 NH2NH2- protein domains tm c -COOH α-chain -COOH β-chain tm c peptide bindig site formed by MHC protein domains peptide α1 α1 α2 β2m α3 Immunoglobulin - like domains α2 β1 β2 plasma membrane -COOH cytosol COOH- -COOH SIMPLIFIED STRUCTURAL MODEL OF THE MHC MOLECULES’ PEPTIDE BINDING SITES a nchoring a mino a cids a nchoring a mino a cids Decapeptide P4 P5 P6 NH P1 P2 P3 P7 P8P9 Octapeptide -2 2 -1 P1 P4 P6 11 COOH NH2 "pockets” P9 10 "pockets” NH2 COOH MHCII MHCI • MHC I has frequently a hydrophobic pocket for the peptide’s C-terminal hydrophobic amino acid side chain • The anchoring amino acid side chains of the peptide’s „core” region fit into evenly distributed binding pockets • The peptide’s terminal -NH3+ and -COO- groups could take part in the anchoring • The ends of the long peptides can extend from the MHC II open binding groove • Peptides with different length could moderately accommodate in the peptide Connections between the T cell receptor’s CDR loops and the MHC-peptide complex The T cell receptor recognize the composite surface made by the MHC molecule and the bound peptide! Generally (but not exclusively): • CDR3 loops bind to the peptide • CDR2 loops bind to the MHC molecule • CDR1 loops bind both the peptide and the MHC molecule • The most variable CDR3 loops form contacts with the most variable part of the MHC-peptide complex (the peptide epitope) • The other variable loops form contacts mainly with the polymorphic MHC molecules General properties of the TCRs and the MHC-TCR connections, and their functional consequences o The antigen receptors assembled randomly from the gene sequences, so they can have various different specificity o T cells “educated” (selected) in the thymus by self MHC molecules. (see next lectures) o Significant surface of the TCR connects only with the MHC molecule. Consequences: • A self TCR “ignores” (can’t bind) most of the foreign MHC: explains MHC restriction The phenomenon of MHC restriction other virus + ’A’ cells Virus ’X’ T cells T T T T T T Mice ’A’ T Virus ’X’ + ’A’ cells T T Mice ’B’ Virus ’X’ Virus ’X’ + cells of ’B’ + cells of ’B’ T T Virus specific T cells can kill the virus infected cells if they derive from the same animals, so if they have identical histocompatibility genes The simplified model of the “MHC restriction” T cell T cell T cell Peptide: MHC: Binding: Peptide: MHC: Binding: APC Peptide: MHC: Binding: APC APC The TCR could bind to the appropriate MHC molecule complexed with the appropriate peptide The TCR recognise the composite surface General properties of the TCRs and the MHC-TCR connections, and their functional consequences o The antigen receptors assembled randomly from the gene sequences, so they can have various different specificity o T cells “educated” (selected) in the thymus by self MHC molecules. (see next lectures) o Significant surface of the TCR connects only with the MHC molecule. Consequences: • A self TCR “ignores” (can’t bind) most of the foreign MHC: explains MHC restriction • Some self TCR can bind strongly to foreign MHC(-peptide) complex: explains alloreaction The rejection is mediated by the genetic (allelic) differences of the histocompatibility genes: ALLOREACTION Beside the beforementioned polimorphic classical peptide presenting MHC molecules, there exist non-polimorphic MHC-like molecules: • MHC class I-like and MHC class II-like molecules • MHC region encoded molecules and molecules encoded outside the MHC region • They have diverse functions Approx. 5% of the T cells in the body are specific for non-peptide epitops presented by non-polymorphic MHC-like molecules! MHC region encoded MHC class Ib proteins and the MODIFICATION OF THE NK CELL FUNCTIONS • HLA-G molecules is expressed on the placental trophoblast cells. They can inhibit the NK cell activation, protect the MHC I non-expressing placental trophoblast cells from the damage by interacting an inhibitory NK cell receptor (LILRB1) Virus infected and tumour cells can express it and exploit its function. HLA-G have also important role in the development of functional placenta by cytokine producing NK cells during the pregnancy You had met them on the previous lectures: • HLA-E molecules expressed on most tissues. They can appear on the cell surface by binding of the signal peptide sequences of HLA-A, B, C proteins and inhibit the NK cell activation (NKG2A:CD94 lectin like NK inhibitory receptor). (They can also present some other peptides with limited diversity, and can activate CTL response.) • MICA, MICB (MHC-class-I-polypeptide-related sequence)(no associated β2 microglobulin) cellular stress induced proteins (infections could also induce stress response in the cell) cell surface expression NK activation and cytotoxicity by the lectin like activatory receptor NKG2D Some MHC class Ib proteins encoded outside the MHC region • MHC class I –like, non-polymorphic molecules encoded also outside the MHC region • MHC I-like structure (β2 microglobulin associated) • Some of it possess antigen presenting function • Some do not have immunological function (or not known at least) MHC class Ib proteins encoded outside the MHC region CD1 proteins: (CD1a, CD1b, CD1c, CD1e • • • • CD1d) usually expressed by professional APCs presenting self and microbial lipids (e.g. glycolipids, lipopeptides) presenting both exogenous and endogenous lipids antibacterial immunity (e.g. immunity against mycobacteria residing in the phagocytes) polar headgroup apolar lipid chain (lipid anchor) NATURE REVIEWS IMMUNOLOGY VOLUME 5 | MAY 2005 | 387- CD1d molecule with bound α-galactosyl ceramide The antigen binding of the CD1 molecules Dirk M Zajonc, Marc A Elsliger, Luc Teyton & Ian A Wilson NATURE IMMUNOLOGY VOLUME 4 NUMBER 8 AUGUST 2003, p808- • The hydrophobic lipid chain is located in the narrow, apolar binding groove • The polar “headgroup” could extend from the CD1 molecule surface • The antigenic epitope compose only a small area on the contact surface of the molecule Recognizing T cells could show slight general autoreactivity to CD1 expressing cells MHC I –like molecule, but MHC II –like, exogenous (endo-lysosomal) antigen presentation Other MHC class Ib proteins encoded outside the MHC region MR1 – molecules are expressed on various cell types (MHC Related-1) They have polar antigen binding site They present microbial riboflavin (vitamin B2) metabolic products and byproducts to mucosa associated invariant T cells (MAIT) Corbet AJ et al.: Nature, 2014 vol509, 361- Many vitamin biosynthetic pathways are unique to bacteria and yeast. Mammals can only acquire riboflavin, so MAIT cells use these metabolites to detect microbial infection. MHC class Ib proteins encoded outside the MHC region MHC class I –like molecules without direct antigen presenting function FcRn – neonatal Fc receptor Transporting IgG (and albumins) to various places of the body. IgG can appear almost in every compartment of the body including epithelial surfaces, secreted fluids, and the phoetus (by transplacental transportation). FcRn can salvage the IgG from the endolysosomal degradation also. IgG have the highest half life time amongst the antibody isotypes. Topics and terms you should know: • • • • • Antigen recognition of T cells Structure of ”classical” MHC I and MHC II molecules Antigen binding properies of MHC molecules Non-classical MHC Ib and MHC-like molecules Heterogenity/polymorphism of MHC molecules (next lectures) Terms: • peptide, protein • antigen, epitop • exon, domain • molecular chaperon • effector T cell/naive T cell • CDR regions of the antigene receptors • motif (of the bound peptide) • (polymorphic) MHC I, MHC II molecules • MHC class Ib • NK cell activation/inhibition • CD1 molecule, FcRn, MR1 The Immune System (P. Parham, 4th ed): chapter 5-6 – 5-10 (p120-126), 5-16 – 5-22 (p132-140) Antigen processing and presentation • • • • • • Endogenous antigen presentation pathway Exogenous antigen presentation pathway Microbial evasion strategies Cross-presentation Lipid presentation Transcriptional regulation of MHC General properties of the MHC-peptide interaction: • MHC molecules can be in a receptive, ”open” conformation until the appropriate peptides bind to them. • The receptive conformation is maintained by the chaperones and the biochemical properties (e.g. pH) of the peptide loading compartment. • Appropriate peptide can induce the conformational change of the MHC molecules. (Appropriate peptide has appropriate binding motif, which allow effective binding to the MHC molecule see the previous lecture) • The bound peptide stabilizes the ”closed” conformation • ”Closed” MHC molecules can detach from the chaperones and reach the cell surface The role of the MHCs’ chaperones • Stabilizing “empty” MHC molecules Empty MHC molecules could become denatured, aggregated and rapidly degraded without chaperones • Retaining or transporting the MHC molecules in the appropriate peptide loading compartment e.g. ER chaperones contain ER retention/targeting signals • Stabilized empty MHC molecules will bind the best fit peptide A better fit peptide can displace the weakly bound peptide (competition) PEPTID EDITING tömör (és kissé elnagyolt) összefoglaló: Az exogén és endogén eredetű fehérje antigének bemutatása (exogén út) (MIIC) (endogén út) DM (TAP) CD4+ Helper T Ii (ER) T CD8+ CTL Synthesis and peptide binding of MHC I molecules Freshly translated ERAAP can trim the peptides to fit Janeway’s Imunolobiology 8th ed © 2012 by Garland Science, Taylor & Francis Group The chaperon complexbound MHC molecule is ready for peptide binding Through the Golgi-network The best fit peptide wins the MHC: PEPTIDE EDITING Proteasomal peptide products could be tailored for MHC I binding 20S subunit of the constitutive proteasome protease subunits The Immune System 4th ed Parham,P (© 2015 by Garland Science, Taylor & Francis Group, LLC) http://www.rcsb.org/pdb/explore.do?structureId=4R3O The ”Immune proteasome” IFN- • new protease subunits replace the others (LMP2, LMP7, MECL-1) • produced peptides are more optimized for MHC I binding protein cleavage preference is changed: hydrophobic or basic amino acid on the C-terminal of the peptide TAP complex transports the peptides into the ER Prefered peptides (for transport): • 8-16 aa length • hydrophobic or basic amino acids at the C-terminal • top view side view Janeway’s Imunolobiology 8th ed (© 2012 by Garland Science, Taylor & Francis Group, LLC) no proline in the first 3 positions (from the Nterminal) The preferences of the TAP correspond to the cleavage specificity of the immune proteasome and the general binding preferences of MHC class I molecules Newly translated MHC II αβ dimers bind to Ii (invariant chain, CD74) chaperon nonameric complex Multimerisation generally turns the low affinity interactions to higher avidity interaction between the complexes α-β-Ii triplex • A part of the Ii chain can fit into the peptide binding site of various MHC II molecules • The bound Ii is blocking the binding site and prevents the binding of ER resident peptides • Ii have endosomal localisation signal sequence Janeway’s Imunolobiology 8th ed © 2012 by Garland Science, Taylor & Francis Group MHC II – Ii complexes travel through the Golgi-apparatus into the endosome The assembly of the [MHC class II molecule – exogenous peptide] complex CLIP peptide peptide editing Janeway’s Imunolobiology 8th ed © 2012 by Garland Science, Taylor & Francis Group CLIP - Class II-associated invariant chain peptide proteases: e.g. cathepsins HLA-DM is a monomorphic MHC class II-like chaperon, which helps in the peptide editing The peptide binding (editing) of the MHC II molecules could take place in a multivesicular/multilamellar endo-lysosomal vesicle: named MIIC or CIIV compartment CIIV – Class II Vesicle or MIIC – MHC class II Compartment Immunity, Vol. 22, 221–233, February, 2005, Copyright ©2005 by Elsevier Inc. DOI 10.1016/j.immuni.2005.01.006 Immuno-electron-microscopy, double immunogold labeling small dots: HLA-DM (10nm nanogold) larger dots: HLA-DR (15nm nanogold) The compartment of the MHC II peptide loading is defined by the presence of HLA-DM Defficiencies of the antigen processing pathways • TAP deficiency: few intra ER peptides low cell surface MHC I expression • tapasin deficiency: altered peptide editing alteration in the MHC I presented peptide repertoire (altered peptide set). More ER derived, fewer cytoplasm (protesome) derived peptides. • B2M (β2 microglobulin) deficiency: impaired MHC class Ia and class Ib expression (e.g. FcRn, CD1, MR1 !) • Ii (invariant chain, CD74) deficiency: alteration in the MHC II presented peptide set (predominant presentation of endogenous peptides) - Altered MHC expression or peptide presentation directly influence the development or the function of the T lymphocytes and NK cells. - This indirectly influences almost all cells of the immune system and the immune response. Pathogens try to interfere with the antigen presentation! Microbes can use different immune evasion strategies Janeway’s Imunolobiology 8th ed © 2012 by Garland Science, Taylor & Francis Group MHC ubiquitination inhibition of the chaperones inhibition of the TAP function Pathogens try to evade the immune response by disabling the MHC I expression of the host cells NK cells possess various inhibitory NK cell receptors which recognise different MHC class I molecules. Decreased or missing MHC I molecule expression on the target cells results NK cell activation. • Absence of polymorphic MHC class I molecules: - HLA-C alleles are potent NK inhibitors (in most of cases) - Lots of HLA-A and HLA-B alleles could also inhibit the NK cell activation with different efficiency • Absence of HLA-E is an indirect indicator of the missing HLA class I translation: HLA-E is a potent NK inhibitor (by NKG2A:CD94). HLA-E cannot leave the ER without binding signal peptides from the classical polymorphic MHC I. Weak HLA-A, -B, -C translation weak HLA-E expression. • activatory signals override the inhibitory signals • NK cell activation killing the cells with ”missing self” (see in the previous lectures also) MHC class II molecules present both exogenous and endogenous peptides (a strong affinity peptide can compete with the invariant chain in the ER) Is special circumstances the MHC I molecules must present exogenous protein derived peptides: Cross-presentation: Cross-presentation: exogenous antigen(!) MHC I molecule(!) • Naive, antigen specific CD8+ T cells need activation by dendritic cells to mature CTL. • Lots of viruses are not able to infect DC, so direct MHC I presentation cannot be achieved • Specialised DC are able to present exogenous antigens by MHC I molecules Effector CTL CELLULAR AND MOLECULAR IMMUNOLOGY 8th ed. (Abbas, AK – Lichtman, AH – Pillai, S) (Elsevier, Saunders 2015) • Endocytosed viral antigens should reach the cytosol to enter the conventional endogenous antigen presentation pathway Lipid presentation by CD1 molecules (MHC-like class Ib) • CD1 synthesis and folding is similar to the conventional MHC I molecules • Lipid transfer proteins (LTP) in the ER or the endosomal system helps to bind or exchange the lipids in the binding site of the CD1 molecules: “LIPID EDITING”) • They can recycle from the cell surface and bind new lipids in the endosomal system NATURE REVIEWS IMMUNOLOGY VOLUME 5 | JUNE 2005 | 485- CD1 molecules can present both endogenous and engulfed exogenous lipids The IFN-γ mediated transcriptional regulation of MHC class I and class II molecule expression and its receptor chains and its receptor chains BioFactors, 42(4):349–357, 2016 • • IFN-γ induced MHC trans activator molecules mediate effective activation of the MHC genes Pro-inflammatory cytokines, or PRR-s can directly or indirectly increase the MHC expression (NF-kB pathway or IFN pathway through the trans activators) The NOD-like trans activators of the MHC genes mediate the formation of large enhanceosome complexes (NLRA) BioFactors, 42(4):349–357, 2016 • The large enhanceosomes can integrate different transcription factors and chromatin remodelling proteins for effective gene activation • CITA enhanceosomes increase the expression of the MHC I presentation pathway’s genes: HLA-A, -B, -C, HLA-E, TAPs, B2M, proteasome subunits, … • CIITA enhanceosomes bind to the promoter regions of the MHC II presentation pathway’s genes: HLA-DR, -DP, -DQ, -DM, -DO, Invariant chain (Ii) and could influence the MHC I genes also in some professional APC-s. Inflammatory mediators can increase the MHC molecule expression of the cells • Strong inflammatory environment results the expression of MHC II molecules by nonprofessional antigen presenting cells also (e.g. endothelia) • IFN-γ induces MHC II expression of the IFN-γ receptor expressing cells (e.g. helper T cells after their activation) Ectopic expression of MHC II molecules exacerbate (increase the severity) of the transplant rejections. Themes and topics (you should know): • Endogenous antigen presentation pathway • Exogenous antigen presentation pathway • Cross-presentation • Main viral evasion strategies • Lipid presentation • Transcriptional regulation of MHC various terms (you should know): • • • • • • • • • • • • • • • • • • • protein, peptide cellular compartments MHC I, MHC II molecules proteasome, immunoproteasome TAP (1, 2) chaperon tapasin signal sequence/peptide protein targeting/sorting Ii (invariant chain), CLIP HLA-DM endosome, MIIC/CIIV peptide editing cross-presentation ”missing-self” theory lipid transport proteins (LTP) “lipid editing” term NLRC5, CIITA trans activators CITA, CIITA enhanceosomes as terms The Immune System (P. Parham, 4th ed): chapter 5-10 – 5-17 (p126-134), 12-14 – 12-17 (p352360), 5-20 (p138) The genetics and heterogeneity of the Major Histocompatibility Complex (MHC) topics, keywords: • • • • • • • • • • Heterogeneity of MHC molecules Mutations Alleles Allele frequency MHC gene region and genes The inheritance of MHC Heterogeneity and expression of MHC class I Heterogeneity and expression of MHC class II Mechanisms of heterogeneity Minor Histocompatibility Antigens Why are so many MHC variants? Multiple MHC variants Various peptide binding „pockets” Multiple various peptide binding specificity • The replication rate of pathogenic microorganisms is faster than human reproduction • The genes of a pathogen can mutate frequently: easily evade the efficient antigen presentation by an MHC molecule To counteract the flexibility of pathogens • The MHC has developed many variants • Some variants could not provide protection from a particular pathogen, but there should be a variant in the genome or in the population which gives efficient protection There are several different MHC molecule variant: POLYMORPHY • The peptide binding domains have the greatest polymorphism • One defined MHC variant can bind various peptides with different sequences but with similar motif • Other MHC variants bind peptides which have different motifs General properties of the MHC molecules: • A given MHC molecule can bind different peptides effectively • A given MHC molecule cannot bind all kinds of peptides • The peptide binding “pockets” of a given MHC molecule restricts which peptides would fit in the set of all peptides peptides presented by a given MHC molecule all peptides • Efficient antigen presentation needs the presence of different MHC molecule variants simultaneously The diversity (polymorphism) of the MHC molecules on the surface of the antigen presenting cells is achieved by multiple ways: peptides presented by different MHC molecules The diversity of the peptid presenting MHC molecules of the individual Polygenic – encoded by multiple genes (evolutionary gene duplications) – ISOTYPES! human MHC class I molecule isotypes: Human: HLA-A, HLA-B, HLA-C genes MHC class II molecule isotypes: Human: HLA-DP, HLA-DQ, HLA-DR genes Polymorphic – genes can have various alleles (allotypes) !!! MHC genes are the most polymorphic known! The genes of the peptide presenting ”classical” MHC molecules have several various alleles in the population. Every isotype can have two alleles in a given heterozygous individual. one gene with different alleles multiple genes, without alleles multiple genes with different alleles HLA – Human Leukocyte Antigen The polymorphy of the HLA-B isotypes in the positions of the pre-matured protein sequences NH2- exons: 1 s 2 α1 3 α2 4 5 tm c -COOH 6 7 8 α3 source: hla.alleles.org signal/leader peptide • α1 α2 • β2m α3 -COOH • • The 2nd and the 3rd exons of the MHC I alpha-chains’ genes are the most polymorphic. The 2nd exon of the alpha and beta chains’ genes of the MHC II could be also polymorphic. They encodes the peptide binding domains. Their sequences are determined by the routine genetic HLA typing. Most polymorphisms derive from point mutations 30 pcs HLA-DPB1 allele sequences between nucleotides 204 and 290 (amino acids 35-68) Y-F A-V DPB1*01011 DPB1*01012 DPB1*02012 DPB1*02013 DPB1*0202 DPB1*0301 DPB1*0401 DPB1*0402 DPB1*0501 DPB1*0601 DPB1*0801 DPB1*0901 DPB1*1001 DPB1*11011 DPB1*11012 DPB1*1301 DPB1*1401 DPB1*1501 DPB1*1601 DPB1*1701 DPB1*1801 DPB1*1901 DPB1*20011 DPB1*20012 DPB1*2101 DPB1*2201 DPB1*2301 DPB1*2401 DPB1*2501 DPB1*26011 DPB1*26012 TAC ---T-TCT-T-T-TCT-T-T-T-T-------T---T-T-T-T-T-TCTCT-T-T-T----- GCG ---T-T-T-T---T-T-T-T-T-T-------T---T-T-T-T-T-T-T-T-T---T----- CGC ------------------------------------------------------------- E-A A-D A-E Silent TTC ------------------------------------------------------------- GAC ------------------------------------------------------------- AGC ------------------------------------------------------------- GAC ------------------------------------------------------------- GTG ------------------------------------------------------------- GGG --A ------------------------A --A ------A ------------------------A --- GAG ------------------------------------------------------------- TTC ------------------------------------------------------------- CGG ------------------------------------------------------------- GCG ------------------------------------------------------------- GTG ------------------------------------------------------------- ACG ------------------------------------------------------------- GAG ------------------------------------------------------------- CTG ------------------------------------------------------------- GGG ------------------------------------------------------------- CGG ------------------------------------------------------------- CCT ------------------------------------------------------------- GCT ---A-AC -AG -A---A-AG -A-A-A-A-------A---A-A-A-AG -A-A-AG -AG ---AG -A----- GCG ---A-A---A---A---A-A-A-A-------A---A-A-A---A-A---------A----- GAG ----------C --------C ----C ----------C ------C ------C --C --------------- TAC ------------------------------------------------------------- I-L TGG ------------------------------------------------------------- AAC ------------------------------------------------------------- AGC ------------------------------------------------------------- CAG ------------------------------------------------------------- AAG ------------------------------------------------------------- Some polymorphism doesn’t influence the peptide binding specificity of the molecules (but mutations in the non-coding promoter/enhancer regions can influence the expression) GAC ------------------------------------------------------------- ATC --------C-------C-------C-C---C-C---------C-C---------C------ CTG ------------------------------------------------------------- GAG ------------------------------------------------------------- GAG ------------------------------------------------------------- MAP OF THE HUMAN MHC FROM THE HUMAN GENOME PROJECT 3.8Mbp ~225 genes (orf) on chromosome 6 × The MHC sequencing consortium Nature 401, 1999 Large gene density! Various protein coding genes, non-protein coding genes (e.g. miRNA), and pseudogenes Properties of the human MHC gene region Located on the short arm (p) of the chromosome 6: telomere class I centromere class III class II divided to 3 subregion depending on the function of the genes: • Class I region: classical polymorphic, endogenous peptide presenting molecules (class Ia). Lots of non-polymorphic MHC I-like class Ib molecules: HLA-E, HLA-F, HLA-G, MICA, MICB molecules (NK cell regulation). • Class II region: classical polymorphic, exogenous peptide presenting molecules. Proteins of the antigen processing: chaperones HLA-DM/, HLADO/, proteasome subunits: LMP2 (PSMB9), LMP7 (PSMB8), peptide transporter subunits (TAP1 and TAP2) genes. • Class III region: !!! Some complement proteins: C4 (polygenic), C2 and factor B, Pro-inflammatory cytokines: Tumor Necrosis Factor (TNF), Limphotoxin (LT) genes All three region contain other genes which could be irrelevant in the immunity and pseudogenes also: pl. cytochrome P450 monooxigenase enzyme (CYP21A2), RNA helicase (DDX39B), casein kinase subunit (CSNK2B), heat shock protein HSP-70 (HSPA1A), sialidase/neuraminidase (NEU1), etc. etc. etc. q p (mirrored orientation compared to the previous ones) Leukocytes were used for the identification of the proteins Human Leukocyte Antigen (HLA) chromosome 6 (Human Leukocyte Antigen) 3 subregion – according the function of the genes mouse chromosome 17 (Histocompatibility-2) × Janeway’s Immunobiology, 8th ed. (Garland Science 2012) The inheritance of the HLA THE HAPLOTYPE MHC I genes: (isotypes) MHC haplotype – the combination of the MHC alleles encoded by one of the diploid chromosome pair B5 B7 B703 B8 B12 B13 B14 B15 B16 B17 B18 B21 B22 B27 B2708 B35 B37 B38(16) B39(16) B3901 B3902 B40 B4005 B41 B42 B44(12) allélok (a populációban) HLA- B: C: Cw1 Cw2 Cw3 Cw4 Cw5 Cw6 Cw7 Cw8 Cw9(w3) Cw10(w3) A1 A2 A203 A210 A3 A9 A10 A11 A19 A23(9) A24(9) A2403 A25(10) A26(10) A28 A29(19) A30(19) A31(19) A32(19) A33(19) A34(10) A36 A43 A66(10) A: Example of a human MHC I haplotype pair One MHC I haplotype of the person: B14, Cw1, A3 The other MHC I haplotype: B8, Cw4, A2 The HLA allele names in the example are the so called ”serotypes” Inheritence of MHC • The MHC region is rather short • Rare meiotic recombinations (linkage) possible combinations in the offsprings DP DQ DR B C • generally the haplotypes are inherited parent 1 DP DQ DR B C A DP B C A DQ DR × parent 2 DP DQ DR B C A DP B C A DQ DR haplotype – allele combination on a haploid chromosome, linked with each other A The genetics and heterogeneity of MHC I (Human Leukocyte Antigen) (Histocompatibility-2) Janeway’s Immunobiology, 8th ed. (Garland Science 2012) 6: q p The heterogeneity of the human MHC class I q 6: diploid individual chromosome 6: MHC I region B haplotype C (maternal origin) B haplotype (paternal origin) codominant expression C A 4358 3492 3111 B A C HLA alleles One individual: generally 6 kind of MHC I molecule A p The genetics and heterogeneity of MHC II (Human Leukocyte Antigen) (Histocompatibility-2) Janeway’s Immunobiology, 8th ed. (Garland Science 2012) 6: q p (animation) The genetics and heterogeneity of the MHC II haplotype (maternal) haplotype (paternal) DR DQ DP A B A B AB A B A B AB HLA-DRA virtually monomorphic The alpha and the beta chains can be combined freely with each other in the ER. But not all combination can result stabile products ! Intraisotype combinations Mixed isotype combinations They are the “preferred” and frequent combinations (random examples) Intrahaplotype combinations DR DR DQ DQ DP DP Cross-haplotype combinations DQ DQ DP DP Some αβ combinations are incompatible – rare combinations ……. summary Mechanisms of the MHC polymorphism • allele variations of the population Principally: combinations of several thousand alleles, Practically: a pair of inherited haplotype combinations of the individual which change rather infrequently by recombinations The large allele numbers result heterozygosity, and the genes of the homologue chromosomes expressed codominantly doubles the number of the HLA isotype variations • MHC gene/molecule isotypes: 3 polymorphic MHC I isotypes: HLA-A, HLA-B, HLA-C 3 polymorphic gene isotype of the MHC II alpha chains: HLA-DPA1, HLA-DQA1, HLA-DRA (monomorphic) and beta chains: HLA-DPB1, HLA-DQB1, HLA-DRB1 (some additional coding subtypes of the HLA-DRB: -3, -4, -5) • α- and β-chain combinations of MHC II 10-12 frequent MHC II αβ combinations (intra isotype combinations) 40 principal combinations by the mixed isotype combinations, but the possibility is very low because of the frequent incompatibility of the mixed isotype αβ chains (protein encoding HLA-DQA2 and HLA-DQB2 subtypes are also described) • alternative splicing (currently only sequence database data indicate them) Alternative splicing could combine the exones between isotypes (and possibly involving the exones of the pseudogene isotypes) THE CLINICAL CONSEQUENCES OF THE MHC POLYMORPHISM • The efficiency of the vaccinations could differ between individuals with different MHC haplotypes • The frequency of some HLA haplotype correlates with the frequency of some disease in different human populations. The correlation can be positive or negative: Some haplotype can protect from the disease and some haplotype could mediate sensitivity against the disease e.g: o Autoimmune diseases o Hypersensitivity disorders The antigen presenting MHC molecules can have direct role in the pathogenesis of these diseases or they simply act as indicators which indicates the presence of other inherited linked alleles in the haplotype: e.g.: the presence of MHC III encoded inflammation mediator gene alleles (TNF alleles, complement factor alleles) Natural selection can change the allele frequency in the populations of different geographical regions which host endemic pathogens • Some MHC allele could provide more efficient protection against a specific pathogen than others This could be observed in the Serotypes Frequency (%) EUR AFR ASI distribution of MHC alleles’ HLA- A1 15.2 5.72 4.48 frequency in different human HLA- A2 28.7 18.9 24.6 geographical populations: HLA- A3 13.4 8.44 2.64 HLA- A28 4.46 HLA- A36 0.02 9.92 1.88 1.76 0.01 • The allele corresponding the HLA-B53 serotype is strongly associated with the recovery from the lethal form of malaria. HLA-B53 serotype is very common in some region where malaria (Plasmodium - parasitic protozoa) is endemic. • HLA-B27 and B57 serotypes have higher allele frequency in the group of ”HIV controllers” THE ROLE OF THE MAJOR HISTOCOMPATIBILITY GENE COMPLEX (MHC) IN THE EFFICIENCY OF THE IMMUNRESPONSE Immunisation: Antigen Antigen mice strain A Strong immunresponse mice strain B Weak / Zero immunresponse Some MHC (allelic) variants can mediate more effective T cell based immune response than other MHC variants! Minor Histocompatibility Antigens (MiHA, MHA, miHA) Minor histocompatibility antigenes (MiHA, MHA, miHA) Antigens which are encoded outside the MHC gene regions , and can induce rejection in the case of transplantation Alloantigens (alleles can be recognised as “non self”) Non polymorphic antigens, sometimes with low allele frequency, so there is low possibility of the incompatibility between a random donor-recipient pair. They are called “minor” because they encoded outside the Major Histocompatibility Complex, but they can mediate severe rejections in transplantations! • MiHA incompatibility could induce rejections even in the case of HLA identity. Their compatibility are also very important in the case of different tissue/organ transplantations. • They can induce miscarriage (abortion) or birth disorders in pregnancy The different groups of the MiHA The classical (strict) definition : Any non-MHC encoded antigen, which mediate immunogenic T cell response in the case of transplantation MiHa antigens are presented by the host MHC molecules MHC I – CD8+ cytotoxic T cell response MHC II – CD4+ helper T cell respone (inflammation) The type of the MHC can limit the presentation (motif!) Approximately 50 well described MiHA are known recently (sequence, MHC restriction) Classical example: H-Y antigen (KDM5D) lysine demethylase enzyme, chromosome Y encoded women could rise immune response against them (every new male embryo become more and more endangered after the previous one in the case of pregnancies) The slack (loose) definition: Any non-MHC encoded alloantigen, or antigens produced by non-self enzymes which could mediate general alloreaction (It could involve T cell, B cell or antibody mediated immune response) e.g.: Rh antigens: The presentation of the antigen mediate the IgG production of the B cells. The pathogenesis are mediated by antibody effector functions. indirect alloreaction: AB0 blood group antigens – 3 glycosyltransferase alleles with high allele frequency can produce different oligosaccharide antigens. The enzymes themselves are not immunogenic. Cross reactions with the microbial flora of the gut induce the immunisation. Endothelial cells can express AB0 antigens. It can induce “immediate type” antibody mediated rejection in mismatched transplantation. The genetics and heterogeneity of MHC Themes and topics (to know): • Heterogeneity of MHC molecules (reasons and consequences) • Mutations, alleles, allele frequency • MHC gene region (Class I, II, III) • The inheritance of MHC • Heterogeneity and expression of MHC class I • Heterogeneity and expression of MHC class II • Mechanisms of heterogeneity • Clinical consequences • Minor Histocompatibility Antigens various terms (you should know): • • • • • • • • • • • • • • • locus gene allele haplotype isotype (of MHC genes) polymorphism polygeny homozygote, heterozygote pseudogene null allele allele frequency exon, domain alternative splicing gene content variation MHC, HLA, MiHA The Immune System (Parham P): chapter 5-18 – 5-23 (4th ed: p135-147)