Presentation on theme: "Viral immune evasion strategies"— Presentation transcript:
1 Viral immune evasion strategies Frank MomburgDivision of Molecular ImmunologyGerman Cancer Research Center, Heidelberg
2 Viral immune evasion strategies 1. Viral evasion of MHC class I-mediated antigen presentation2. Viral evasion of MHC class II-mediated antigen presentation3. Viral evasion of natural killer cell activation4. Viral interference of chemokine/cytokine action5. Viral evasion of antibody responses and complement attack6. Viral interference with apoptosis
3 Life styles and survival strategies of viruses „hit and run“„hit and hide“Small RNA viruse.g. human influenza virusLarge DNA viruse.g. CMVInterference with innate immunity, typically type I interferonBlockade of host gene transcriptionAntigenic hypervariabilityInterference with adaptive immunityReplication at immunoprivileged sitesMolecular latencyIn most cases: elimination of the virusPersistent infection
4 Cytomegalovirus genome (235 kbp, > 200 open reading frames) Hepatitis B virusInfluenzavirusAdenovirusVaccinia virusCMV
5 Antigenic drift and antigenic shift of influenza virus
6 Acute infection and latent phase (herpes simplex virus)
9 Presentation of antigenic peptides by MHC class I molecules Cytotoxic T cellCbCaT cell receptorVbVaa1a2CD8 coreceptorb2ma3Antigen presenting cell
10 Role of MHC class I-mediated antigen presentation in antiviral immune responses The antigen-specific T cell receptors of CD8+ cytotoxic T cells (CTL) recognize MHC class I molecules displayed on the surface of virus-infected cells or on professional antigen presenting cells (dendritic cells, macrophages, B cells).These MHC-I molecules present peptide antigens that are cleaved out of endogenously synthesized viral proteins by proteasomes and other intracellular proteases. Alternatively, viral antigens can be cross-presented by professional APC after uptake of viral particles or of apoptotic, virus-infected cells.
11 Viral subversion of MHC class I-mediated antigen presentation 1. Interference with the biosynthesis of MHC-I moleculesAdenovirus E1A Transcriptional inhibition (via decrease of NFB) of MHC-I heavy chain, TAP1/2, and LMP2/7 expression2. Interference with antigen processing by proteasomesHCMV pp65 Kinase (IE phase), inhibits generation of antigenic peptides from a 72 kDa transcription factor (important antigen in immediate early phase)EBV EBNA-1 Contains a 239 residue Gly-Ala repeat that blocks proteasomal processingMuLV env-p15E Single amino acid change (K R) in FMR subtypes loss of CTL epitope through altered proteasomal cleavage site
12 Viral subversion of MHC class I-mediated antigen presentation 2. Interference with antigen processing by proteasomesHCMV pp65 Kinase (IE phase), inhibits generation of antigenic peptides of a 72 kDa transcription factor (important antigen in immediate early phase)EBV EBNA-1 Contains a 239 residue Gly-Ala repeat that blocks proteasomal processingMuLV env-p15E Single amino acid change (K R) in FMR subtypes loss of CTL epitope through altered proteasomal cleavage site
13 Viral subversion of MHC class I-mediated antigen presentation 3. Interference with peptide transport by TAPHSV1/2 ICP47 Cytosolic protein blocking peptide binding to TAPHCMV US6 ER protein that inhibits peptide translocation (inducing a conformational change that prevents ATP binding to TAP1)BHV/EHV/PRV UL Inhibition of peptide translocation (inducing a transport-incompetent arrest and proteasomal degradation of TAP)HIV ? Inhibition of TAP
14 Viral subversion of MHC class I-mediated antigen presentation 4. Interference with the heterotrimeric assembly of MHC-I molecules in the ERHCMV US2, US11 Dislocation of MHC-I through the Sec61p channel to the cytosol proteasomal degradationHIV Vpu Dislocation from ER to cytosol proteasomal degradationAdenovirus E3/19K Retains MHC-I in the ER, inhibits TAP/tapasin associationHCMV US3 Retains MHC-I in the ER, inhibition of tapasin- dependent peptide loadingMHV-68 mK3 Ubiquitination/degradation of TAP/tapasin associated MHC-IHPV E5 Retains MHC-I in the Golgi complex
15 Viral factors interfering with the peptide loading complex and assembly of MHC class I molecules
16 Retrotranslocation of MHC class I molecules from the ER to the cytosol for proteasomal degradation
17 Viral subversion of MHC class I-mediated antigen presentation 5. Interference with the intracellular trafficking of MHC-I moleculesMCMV m152/gp40 Retains MHC-I in cis-Golgi networkMCMV m04/gp34 Blocks antigen presentation by MHC-I on the cell surfaceMCMV m06/gp48 Targets MHC-I to late endosomes/lysosomes degradationHPV E5 Retains MHC-I in the Golgi complexHIV Nef Enhanced endocytosis of MHC-I sequestration in trans-Golgi networkHHV-8(KSHV) K3, K5 Enhanced endocytosis of HLA-A, B, (C, E), ubiquitination/degradationHHV-7 U21 Diversion of MHC-I molecules to lysosomes degradation
18 Viral factors obstructing the intracellular trafficking of MHC class I molecules
19 Viral inhibition of MHC class I-mediated antigen presentation 6. Mutation of CTL epitopesMutations in class I-binding peptides represent an important mechanism to prevent antiviral CTL responses, leading to loss of MHC-I binding, loss of CTL recognition, or antagonism of an existing CTL response.HIV, EBV, HBV, HCV, Influenza virus
20 Multiple immune evasion mechanisms employed by HIV
21 Role of MHC class II-mediated antigen presentation in antiviral immune responses Viruses that enter cells through phagocytosis or receptor-mediated endocytosis, or that are enveloped in the trans-Golgi network/early endosome, can undergo degradation into antigenic peptides through the action of endosomal/lysosomal proteases. Such peptides are loaded onto MHC class II (MHC-II) molecules for presentation to CD4+ T cells.MHC-II molecules are constitutively expressed only by B cells, macrophages, dendritic cells and endothelial cells, however, can be induced on a variety of other cell types by IFN- in the course of inflammtory responses.Activated CD4+ T cells function as helper T cells assisting the maturation of CD8+ CTL and thus coordinate antiviral responses, or may possess CTL activity themselves (in humans).
22 MHC class II-mediated presentation of exogenous viral antigens
23 MHC class II-mediated presentation of endogenous viral antigens
24 Viral evasion of MHC class II-mediated antigen presentation 1. Interference with the biosynthesis of MHC-II moleculesMCMV M27 IFN-induced transcriptional upregulation of MHC-II expression inhibited (interference with Jak1/STAT pathway CIITA)Adenovirus E1A IFN-induced transcriptional upregulation of MHC-II expression inhibited
26 Viral evasion of MHC class II-mediated antigen presentation 2. Interference with the intracellular trafficking of MHC-II moleculesHCMV US2 Dislocation of MHC-II to cytosol proteasomal degradationEBV BZLF2 Association with HLA-DR(DP, DQ) chains on the cell surface inhibition of antigen presentationBPV E6 Interaction with AP-1 adaptor protein disturbs intracellular transportBPV/HPV E5 Interaction with 16K subunit of the vacuolar ATPase endosomal acidification and MHC-II processing
27 Viral interference with MHC class II-mediated antigen presentation
28 Viral inhibition of MHC class II-mediated antigen presentation 3. Interference with the costimulatory molecule CD4 (T helper cells)HIV-1,-2, SIV Nef Endocytosis of CD4 via AP-2 adaptor complex (endocytosis motif in Nef), transport to lysosomes via COPI associationHIV-1 Vpu Induction of CD4 ubiquitination in the ER dislocation to the cytosol proteasomal degradationMyxoma virus ? Internalization of CD4 lysosomal degradationT cell receptorMHC-II/peptidea1b1b2VbVaCbCaCD4 coreceptorHelper T cellAntigen presenting cella2
29 Molecular mechanisms employed by the HIV Nef protein
30 Role of NK cells in antiviral immune responses Natural Killer (NK) cells are important effector components of the innate immune system that function in the initial defense against viruses via direct cellular cytotoxicity and through the production of inflammatory cytokines that promote the influx of CD8+ T cells.For the control of certain viral infections in mice (RSV, MCMV), an early NK-mediated cytotoxicity and IFN- production plays an important role. In humans, a congenital lack of NK cells is associated with severe herpesvirus infections and low NK cell numbers correlate with more rapid progession towards AIDS in HIV-positive patients.NK cells are preferentially activated in the presence of low amounts of MHC-I molecules ("missing self") since particular allelic variants of polymorphic MHC-I molecules trigger inhibitory NK receptors.
32 Viral evasion of NK cell activation 1. MHC-I homologs binding to inhibitory NK receptorsMCMV m144 Peptide-free MHC-I homolog, 2-microglobulin- associated, inhibitory NK receptor unknownMCMV m157 Distant MHC-I homolog; binding to Ly49I inhibitory receptor in CMV-susceptible mouse strain, to Ly49H activating receptor in CMV-resistant strainHCMV UL18 MHC-I homolog, 2-microglobulin and peptide- associated, binds to NK-inhibitory LIR-1/ILT-2 receptor
33 Viral evasion of NK cell lysis 2. Selective expression of NK-inhibitory MHC-I moleculesHIV-1 Nef No downregulation of NK-inhibitory HLA-C, -E, -G moleculesHCMV US2, US No downregulation of NK-inhibitory HLA-C, -E, -G moleculesHCMV UL Encodes a leader sequence-derived peptide that is loaded onto inhibitory HLA-E molecules in a TAP-independent fashion3. Downmodulation of costimulatory moleculesHHV-8 K5 Decreased surface expression and ubiquitination of costimulatory (KSHV) ICAM-1 and B7-2 moleculesHCV E2 Ligation of costimulatory CD81(TAPA-1) tretaspan molecule
35 TAP-independent NK cell inhibition by HLA-E and the HCMV UL40 protein
36 Viral evasion of NK cell lysis 4. Inhibition of NK-activating ligandsHCMV UL16 Intracellular retention of the NK cell activating NKG2D ligands MICB and ULBP1,2 (does not affect MICA and ULBP3)MCMV m152/gp40 Inhibits surface expression of NK activating ligand H-60
38 Role of cytokines and chemokines in antiviral responses Cytokines and chemokines are secreted polypeptides that coordinate inflammation, cellular activation, proliferation, differentiation, and chemotaxis.Cytokines and chemokines are immune mediators that are produced early upon virus infection. They induce and maintain innate as well as adaptive immune responses. Cytokines are responsible for flu-like symptoms such as myalgia, fever, headache and drowsiness which are common manifestations of acute virus infections.Cytokines can be powerful antiviral mediators, allowing clearance of virus infection in the majority of cases. Double-stranded viral RNA type-I interferons (IFN-/) protein translation , cell proliferation , cellular RNases for viral RNA .Pro-inflammatory cytokines are of particular importance and frequently targeted by viruses: IL-1, IL-12, TNF-, IFN-/, IFN-, and several chemokines that activate leukocyte migration.
39 Viral evasion of cytokine action 1. Interruption of cytokine production and maturationAdenovirus E1A Blocks IRF-3-induced transcription of IFN-/HPV E Blocks IRF-3-induced transcription of IFN-/HCMV ? Inhibition of transcription of MCP-1 chemokineMyxoma virus SERP Inhibition of IL-1 converting enzyme (ICE) IL-1 Cowpox virus CrmA/Spi Inhibits several caspases, including ICEVaccinia virus B13R Inhibits several caspases, including ICEMeasles virus Hemagglutinin Binding to CD46 (complement receptor/regulator for C3b/C4b) on infected macrophages/DC IL-12 production Th1 response (IFN- production by T and NK cells)
41 Viral evasion of chemokine/cytokine action 2. Interference with the receipt of the chemokine/cytokine signalA. Viral chemokine receptor homologsHCMV US28 Functional CCR1 chemokine receptor (binds MCP-1, MIP-1, RANTES), co-receptor for HIV entryHCMV UL33 CCR1 chemokine receptor, expressed in viral coatMCMV M33 CCR1 homolog, role in salivary gland dissemination and replicationHVS ECRF3 Functional CXCR2 chemokine receptorHHV-8 ORF74 Constitutively active, agonist-independent CXCR2 receptorHHV-6/7 ? Downregulation of cellular CXCR4 chemokine receptor in infected CD4+ T cells response to ligand SDF-1 B. Viral chemokine/cytokine homologsHHV-8 vMIP-II Broad spectrum CC-, CXC- and CX3C chemokine antagonistMCV MC-148P Broad spectrum CC- and CXC chemokine antagonistHHV-8 vMIP-I MIP-1 homolog, CCR8 agonist, Th2 response HHV-6 U83 MIP-1 homolog, CC chemokine agonistMCMV m131 CC chemokine homolog, promotes virus disseminationHHV-8 vIL-6 IL-6 homolog, increases angiogenesis and hematopoesis (role in Kaposi sarkoma, IL-6R+)EBV vIL-10 IL-10 homolog, antagonizes Th1 responsesMCV MC-51L Secreted, binds IL-18 NK activation, Th1 responseC. Virus-encoded secreted cytokine receptors and chemokine-binding proteinsCowpox virus CrmB, CrmC Secreted TNF-R homologs, sequester TNF- and LT-Myxoma virus MT Secreted TNF-R homolog, sequesters and inhibits TNF-HCMV UL TNF-R homolog, retained intracellularlyVaccinia virus B18-R Secreted type I IFN-R homolog, sequesters IFN-Vaccinia virus B8-R Secreted type II IFN-R homolog, sequesters IFN-Myxoma virus M-T Secreted type II IFN-R homolog, sequesters IFN-Vaccinia virus B15-R Secreted IL-1-R homolog, sequesters IL-1EBV BARF Secreted protein, sequesters CSF-1
42 Viral evasion of chemokine/cytokine action 3. Interference with interferon-mediated effector functionsA. Inhibition of IFN-induced gene transcriptionAdenovirus E1A Depletion of STAT1 or p48 ISGF3 IFN-induced transcriptional activation HPV E7 Sequestering of IRF1 IFN-induced gene transcription HCMV ? Depletion of Jak1 kinase and p48 ISGF3 HHV-8 vIRF K9 IRF antagonist, competition with IFN-induced transcriptionB. Interference with IFN-induced cellular defence mechanismsEBV EBNA2 IRF antagonist, competition with IFN-induced transcriptionHCV E2 Inhibits phosphorylation of eIF2 by dsRNA-dependent protein kinase (PKR)HSV Activates protein phosphorylase 1 to dephosphorylate eIF2Vaccinia virus K3L eIF2 homolog, inhibits PKRAdenovirus VAI RNA Viral RNA, inhibits PKREBV EBER I Viral RNA, inhibits PKRVaccinia virus E3L Sequesters ds-RNA, prevents PKR and 2’5’-OS activationHSV '-5'-(A) analog Inhibits 2'-5'-oligoadenylate synthase RNaseL activity
43 Viral evasion of antiviral cytokine effector functions
44 Role of antibodies and complement in antiviral reponses Protective antibodies bind to virus surface structures and can block their interaction with cellular receptors.Antibody-tagged (opsonized) viruses can be cleared from the circulation via IgG-Fc receptors expressed by phagocytes or by germinal center follicular dendritic cells ( viral spread possible).Fc receptors (CD16) instruct NK cells to lyse antibody-coated virus-infected cells by antibody-dependent cellular cytotoxicity (ADCC).IgM- and IgG-coated viruses can be neutralized by the classical complement pathway.Viruses tagged with the complement component C3b (or C4b, C3bi) can be phagocytosed via the CR1 (CD35) complement receptor.Viruses coated with C3b cleavage products (C3d, C3bi) can activate the CR2 (CD21) complement receptor of B cells. Follicular dendritic cells expressing CR1/CR2 complement receptors trap opsonized viruses and stimulate antibody production by germinal center B cells.Phagocytosis of opsonized viruses elicits antigen processing, release of pro-inflammatory cytokines and T cell activation. Byproducts of the complement pathway (C3a, C4a, C5a) function as chemotactic peptides and amplify the inflammatory process.
46 Viral evasion of antibody responses Viral Fc receptor homologsHSV-1 gE-gI FcR homolog for monomeric or aggregated IgG, expressed on virus particles or infected cells, gE contains YXXL internalization motif for endocytosis of immune complexes inhibition of ADCCHSV-2 gE FcR homologMCMV Fcr1 FcR homologPRV gE-gI FcR homologVZV gE-gI FcR homologMV NP Ligates cellular inhibitory FcRII receptor (CD32)downregulation of antibody production by B cells
47 Evasion of antibody responses by viral Fc receptors
51 Viral interference with apoptosis (programmed cell death) Replicating viruses may stimulate suicide of the host cell directly or provoke recognition by cytolytic T cells and NK cells.These immune effector cells induce apoptosis by secretion of cytotoxic cytokines (such as TNF) and by processes requiring direct cell-cell contact (perforin/granzyme system or CD95/CD95-L system).Premature cell death would limit the time available for the production of new virions and interrupt cycles of latency and reactivation used by persistent viruses.
53 Viral evasion of the extrinsic apoptosis pathway 1. Inhibition of TNF/Fas-mediated apoptosisMyxoma virus MT-2 TNF-R homolog, secreted form blocks TNF- induced apoptosis, intracellular form protects T cells from apoptosisCowpox virus CrmB, C, D Secreted TNF-R homologs, neutralize TNF- and LT-Adenovirus E3-10.4/ Multimeric complex (RID) that forces internalization and K lysosomal degradation of CD95 (Fas, APO-1)HCMV UL TNF-R homolog, retained intracellularly, function unclear2. Death effector domain (DED)-containing viral proteins (vFLIPs)HHV-8 K Viral FLICE inhibitory proteins (vFLIPs) with 2 DEDs, bindHVS ORF FADD/TRADD adaptor proteins, prevent activation ofMCV MC159, FLICE (Caspase-8)/Caspase-10 following ligation of CD95,BHV-4 BORFE TNFR1, TRAMP, TRAIL-R1/R2 death receptors
54 Viral regulation of the extrinsic apoptosis pathway
56 Viral regulation of the intrinsic apoptosis pathway
57 Viral immune evasion strategies Co-evolution of viruses with their hosts for millions of years has led to a host immune system of high complexicity and, likewise, sophisticated viral mechanisms to antagonize immunity.Viral antagonists interfere with all relevant effector pathways of the innate and the adaptive immune system includingthe MHC class I-mediated antigen presentation activating cytotoxic T cellsthe MHC class II-mediated antigen presentation activating helper T cellsthe activation of natural killer cellsthe function chemokines and cytokines orchestrating cellular antiviral responsesthe function of antiviral antibodiesthe function of the complement systemthe induction of the extrinsic and intrinsic pathways of programmed cell death