Transcript HCMV - ZMBH
Viral immune evasion strategies Frank Momburg Division of Molecular Immunology German Cancer Research Center, Heidelberg [email protected] Viral immune evasion strategies 1. Viral evasion of MHC class I-mediated antigen presentation 2. Viral evasion of MHC class II-mediated antigen presentation 3. Viral evasion of natural killer cell activation 4. Viral interference of chemokine/cytokine action 5. Viral evasion of antibody responses and complement attack 6. Viral interference with apoptosis Life styles and survival strategies of viruses „hit and run“ „hit and hide“ Small RNA virus e.g. human influenza virus Large DNA virus e.g. CMV Interference with innate immunity, typically type I interferon Blockade of host gene transcription Antigenic hypervariability Interference with adaptive immunity Replication at immunoprivileged sites Molecular latency In most cases: elimination of the virus Persistent infection Cytomegalovirus genome (235 kbp, > 200 open reading frames) Q N A C B G F M K H L C D J I OP E HindIII Hepatitis B virus Influenzavirus Adenovirus Vaccinia virus CMV Antigenic drift and antigenic shift of influenza virus Zur Anzeige wird der QuickTime™ Dekompressor „TIFF (Unkomprimiert)“ benötigt. Acute infection and latent phase (herpes simplex virus) Zur Anzeige wird der QuickTime™ Dekompressor „TIFF (Unkomprimiert)“ benötigt. Viruses involved in immune escape Herpesviruses HSV1,2 Herpes simplex virus types 1, 2 VZV Varicella zoster virus HCMV Human cytomegalovirus MCMV Mouse cytomegalovirus EBV Epstein Barr virus BHV-4 Bovine herpesvirus 4 EHV Equine herpes virus PRV Pseudorabies virus HVS Herpesvirus saimiri HHV-6,7,8 Human herpesvirus types 6, 7, 8 MHV-68 Mouse 2-herpesvirus 68 Poxviruses Myxoma virus Cowpox virus Vaccinia virus Molluscum contagiosum virus Variola virus Papovaviruses BPV Bovine papilloma virus HPV Human papilloma virus SV40 Simian virus 40 Retroviruses HIV Human immunodeficiency virus SIV Simian immunodeficiency virus MuLV Murine leukemia virus Others Adenovirus Influenzavirus RSV Respiratory syncytial virus MV Measles virus HCV Hepatitis C virus HBV Hepatitis B virus The innate and the adaptive immune system Presentation of antigenic peptides by MHC class I molecules Cytotoxic T cell T cell receptor Cb C a Vb Va a1 a2 b 2m a3 CD8 coreceptor Antigen presenting cell 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. Viral subversion of MHC class I-mediated antigen presentation 1. Interference with the biosynthesis of MHC-I molecules Adenovirus E1A Transcriptional inhibition (via decrease of NFB) of MHC-I heavy chain, TAP1/2, and LMP2/7 expression 2. Interference with antigen processing by proteasomes HCMV 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 processing MuLV env-p15E Single amino acid change (K R) in FMR subtypes loss of CTL epitope through altered proteasomal cleavage site Viral subversion of MHC class I-mediated antigen presentation 2. Interference with antigen processing by proteasomes HCMV 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 processing MuLV env-p15E Single amino acid change (K R) in FMR subtypes loss of CTL epitope through altered proteasomal cleavage site Viral subversion of MHC class I-mediated antigen presentation 3. Interference with peptide transport by TAP HSV1/2 ICP47 Cytosolic protein blocking peptide binding to TAP HCMV US6 ER protein that inhibits peptide translocation (inducing a conformational change that prevents ATP binding to TAP1) BHV/EHV/PRV UL49.5 Inhibition of peptide translocation (inducing a transport-incompetent arrest and proteasomal degradation of TAP) HIV ? Inhibition of TAP Viral subversion of MHC class I-mediated antigen presentation 4. Interference with the heterotrimeric assembly of MHC-I molecules in the ER HCMV US2, US11 Dislocation of MHC-I through the Sec61p channel to the cytosol proteasomal degradation HIV Vpu Dislocation from ER to cytosol proteasomal degradation Adenovirus E3/19K Retains MHC-I in the ER, inhibits TAP/tapasin association HCMV US3 Retains MHC-I in the ER, inhibition of tapasindependent peptide loading MHV-68 mK3 Ubiquitination/degradation of TAP/tapasin associated MHC-I HPV E5 Retains MHC-I in the Golgi complex Viral factors interfering with the peptide loading complex and assembly of MHC class I molecules Retrotranslocation of MHC class I molecules from the ER to the cytosol for proteasomal degradation Viral subversion of MHC class I-mediated antigen presentation 5. Interference with the intracellular trafficking of MHC-I molecules MCMV m152/gp40 Retains MHC-I in cis-Golgi network MCMV m04/gp34 Blocks antigen presentation by MHC-I on the cell surface MCMV m06/gp48 Targets MHC-I to late endosomes/lysosomes degradation HPV E5 Retains MHC-I in the Golgi complex HIV Nef Enhanced endocytosis of MHC-I sequestration in trans-Golgi network HHV-8(KSHV) K3, K5 Enhanced endocytosis of HLA-A, B, (C, E), ubiquitination/degradation HHV-7 U21 Diversion of MHC-I molecules to lysosomes degradation Viral factors obstructing the intracellular trafficking of MHC class I molecules Viral inhibition of MHC class I-mediated antigen presentation 6. Mutation of CTL epitopes Mutations 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 Multiple immune evasion mechanisms employed by HIV Role of MHC class II-mediated antigen presentation in antiviral immune responses • Viruses that enter cells through phagocytosis or receptormediated 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). MHC class II-mediated presentation of exogenous viral antigens MHC class II-mediated presentation of endogenous viral antigens Viral evasion of MHC class II-mediated antigen presentation 1. Interference with the biosynthesis of MHC-II molecules MCMV 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 Interferon pathways Viral evasion of MHC class II-mediated antigen presentation 2. Interference with the intracellular trafficking of MHC-II molecules HCMV US2 Dislocation of MHC-II to cytosol proteasomal degradation EBV BZLF2 Association with HLA-DR(DP, DQ) b chains on the cell surface inhibition of antigen presentation BPV E6 Interaction with AP-1 adaptor protein disturbs intracellular transport BPV/HPV E5 Interaction with 16K subunit of the vacuolar ATPase endosomal acidification and MHC-II processing Viral interference with MHC class IImediated antigen presentation 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 COPIb association HIV-1 Vpu Induction of CD4 ubiquitination in the ER dislocation to the cytosol proteasomal degradation Myxoma virus ? Internalization of CD4 lysosomal degradation Helper T cell T cell receptor MHC-II/peptide Cb Ca Vb Va CD4 coreceptor a1 b 1 a2 b 2 Antigen presenting cell Molecular mechanisms employed by the HIV Nef protein 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. Activation and inhibition of NK cells Viral evasion of NK cell activation 1. MHC-I homologs binding to inhibitory NK receptors MCMV m144 Peptide-free MHC-I homolog, b2-microglobulinassociated, inhibitory NK receptor unknown MCMV m157 Distant MHC-I homolog; binding to Ly49I inhibitory receptor in CMV-susceptible mouse strain, to Ly49H activating receptor in CMV-resistant strain HCMV UL18 MHC-I homolog, b2-microglobulin and peptideassociated, binds to NK-inhibitory LIR-1/ILT-2 receptor Viral evasion of NK cell lysis 2. Selective expression of NK-inhibitory MHC-I molecules HIV-1 Nef No downregulation of NK-inhibitory HLA-C, -E, -G molecules HCMV US2, US11 No downregulation of NK-inhibitory HLA-C, -E, -G molecules HCMV UL40 Encodes a leader sequence-derived peptide that is loaded onto inhibitory HLA-E molecules in a TAP-independent fashion 3. Downmodulation of costimulatory molecules HHV-8 (KSHV) K5 Decreased surface expression and ubiquitination of costimulatory ICAM-1 and B7-2 molecules HCV E2 Ligation of costimulatory CD81(TAPA-1) tretaspan molecule Viral mechanisms for evading NK cells TAP-independent NK cell inhibition by HLA-E and the HCMV UL40 protein Viral evasion of NK cell lysis 4. Inhibition of NK-activating ligands HCMV 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 Inhibition of NK cell activation by HCMV UL16 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-a/b) 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-a, IFN-a/b, IFN-, and several chemokines that activate leukocyte migration. Viral evasion of cytokine action 1. Interruption of cytokine production and maturation Adenovirus E1A Blocks IRF-3-induced transcription of IFN-a/b HPV E6 Blocks IRF-3-induced transcription of IFN-a/b HCMV ? Inhibition of transcription of MCP-1 chemokine Myxoma virus SERP-2 Inhibition of IL-1b converting enzyme (ICE) IL-1b Cowpox virus CrmA/Spi-2 Inhibits several caspases, including ICE Vaccinia virus B13R Inhibits several caspases, including ICE Measles 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) Viral interference with chemokine action Viral evasion of chemokine/cytokine action 2. Interference with the receipt of the chemokine/cytokine signal A. Viral chemokine receptor homologs HCMV HCMV MCMV HVS HHV-8 HHV-6/7 US28 UL33 M33 ECRF3 ORF74 ? Functional CCR1 chemokine receptor (binds MCP-1, MIP-1ab, RANTES), co-receptor for HIV entry CCR1 chemokine receptor, expressed in viral coat CCR1 homolog, role in salivary gland dissemination and replication Functional CXCR2 chemokine receptor Constitutively active, agonist-independent CXCR2 receptor Downregulation of cellular CXCR4 chemokine receptor in infected CD4+ T cells response to ligand SDF-1 B. Viral chemokine/cytokine homologs HHV-8 MCV HHV-8 HHV-6 MCMV HHV-8 EBV MCV vMIP-II MC-148P vMIP-I U83 m131 vIL-6 vIL-10 MC-51L Broad spectrum CC-, CXC- and CX3C chemokine antagonist Broad spectrum CC- and CXC chemokine antagonist MIP-1b homolog, CCR8 agonist, Th2 response MIP-1a homolog, CC chemokine agonist CC chemokine homolog, promotes virus dissemination IL-6 homolog, increases angiogenesis and hematopoesis (role in Kaposi sarkoma, IL-6R+) IL-10 homolog, antagonizes Th1 responses Secreted, binds IL-18 NK activation, Th1 response C. Virus-encoded secreted cytokine receptors and chemokine-binding proteins Cowpox virus Myxoma virus HCMV Vaccinia virus Vaccinia virus Myxoma virus Vaccinia virus EBV CrmB, CrmC MT-2 UL144 B18-R B8-R M-T7 B15-R BARF-1 Secreted TNF-R homologs, sequester TNF-a and LT-a Secreted TNF-R homolog, sequesters and inhibits TNF-a TNF-R homolog, retained intracellularly Secreted type I IFN-R homolog, sequesters IFN-a Secreted type II IFN-R homolog, sequesters IFN- Secreted type II IFN-R homolog, sequesters IFN- Secreted IL-1b-R homolog, sequesters IL-1b Secreted protein, sequesters CSF-1 Viral evasion of chemokine/cytokine action 3. Interference with interferon-mediated effector functions A. Inhibition of IFN-induced gene transcription Adenovirus HPV HCMV HHV-8 E1A E7 ? vIRF K9 Depletion of STAT1 or p48 ISGF3 IFN-induced transcriptional activation Sequestering of IRF1 IFN-induced gene transcription Depletion of Jak1 kinase and p48 ISGF3 IRF antagonist, competition with IFN-induced transcription B. Interference with IFN-induced cellular defence mechanisms EBV HCV HSV Vaccinia virus Adenovirus EBV Vaccinia virus HSV EBNA2 E2 134.5 K3L VAI RNA EBER I E3L 2'-5'-(A) analog IRF antagonist, competition with IFN-induced transcription Inhibits phosphorylation of eIF2a by dsRNA-dependent protein kinase (PKR) Activates protein phosphorylase 1a to dephosphorylate eIF2a eIF2a homolog, inhibits PKR Viral RNA, inhibits PKR Viral RNA, inhibits PKR Sequesters ds-RNA, prevents PKR and 2’5’-OS activation Inhibits 2'-5'-oligoadenylate synthase RNaseL activity Viral evasion of antiviral cytokine effector functions 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. Fc receptors Viral evasion of antibody responses Viral Fc receptor homologs HSV-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 ADCC HSV-2 gE FcR homolog MCMV Fcr1 FcR homolog PRV gE-gI FcR homolog VZV gE-gI FcR homolog MV NP Ligates cellular inhibitory FcRII receptor (CD32) downregulation of antibody production by B cells Evasion of antibody responses by viral Fc receptors The complement pathways and their regulation Viral subversion of complement responses 1. Enhanced factor I-mediated inactivation of C3b, C4b, or C3 convertases by viral proteins mimicking regulators of complement activation (RCA) HSV1/2 gC-1/2 CR1(CD35) homolog HVS ORF-4 C4b-BP, CD46(MCP), CD55(DAF) homolog HHV-8 CCPH C4b-BP, CD46(MCP), CD55(DAF) homolog Cowpox virus IMP C4b-BP homolog Vaccinia virus VCP C4b-BP homolog Variola virus SPICE C4b-BP homolog HCMV ? upregulation of host cell CD46 and CD55 HIV ? downregulation of host cell CR1/CR2, recruitment of factor H by gp41 and gp120 2. Inhibition of C9 polymerisation HVS HVS-CD59 CD59(MIRL) homolog Viral evasion of complement activation 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 TNFa) 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. Molecular pathways of apoptosis Viral evasion of the extrinsic apoptosis pathway 1. Inhibition of TNF/Fas-mediated apoptosis Myxoma virus MT-2 Cowpox virus Adenovirus CrmB, C, D E3-10.4/ 14.5K UL144 HCMV TNF-R homolog, secreted form blocks TNF-a induced apoptosis, intracellular form protects T cells from apoptosis Secreted TNF-R homologs, neutralize TNF-a and LT-a Multimeric complex (RID) that forces internalization and lysosomal degradation of CD95 (Fas, APO-1) TNF-R homolog, retained intracellularly, function unclear 2. Death effector domain (DED)-containing viral proteins (vFLIPs) HHV-8 HVS MCV BHV-4 K13 ORF71 MC159, 160 BORFE2 Viral FLICE inhibitory proteins (vFLIPs) with 2 DEDs, bind FADD/TRADD adaptor proteins, prevent activation of FLICE (Caspase-8)/Caspase-10 following ligation of CD95, TNFR1, TRAMP, TRAIL-R1/R2 death receptors Viral regulation of the extrinsic apoptosis pathway Viral evasion of the intrinsic apoptosis pathway 3. Viral caspase inhibitors Cowpox virus Vaccinia virus Baculoviruses Adenovirus CrmA/SPI-2 SPI-2/B13R2 p35 vIAP 14.7K Serpin, inhibits caspase-8, caspase-1 (ICE), granzyme B Serpin, inhibits caspase-8, caspase-1 (ICE), granzyme B Inhibits multiple caspases Inhibits initiator caspase-9 and effector caspases-3 and -7 Inhibits caspase-8 4. Viral antiapoptotic Bcl-2 homologs EBV HHV-8, HVS Adenovirus EBV BHRF1 BALF1 ORF16 E1B/19K LMP-1 Bcl-2 homologs, prevent cytochrom c release from mitochondria activation of caspase-9 dito dito Bcl-2 transcription mimics anti-apoptotic TNF-R signals Viral regulation of the intrinsic apoptosis pathway 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 including the MHC class I-mediated antigen presentation activating cytotoxic T cells the MHC class II-mediated antigen presentation activating helper T cells the activation of natural killer cells the function chemokines and cytokines orchestrating cellular antiviral responses the function of antiviral antibodies the function of the complement system the induction of the extrinsic and intrinsic pathways of programmed cell death