Herpesviruses PDF

Herpesviruses Dana Koptides, PhD 31 October 2024 Herpesviruses - Outline General features of human herpesviruses Classification Replication and Structure Herpesvirus latency Pathogenesis and treatment of different human herpesvirus disorders Herpesviruses - General features Ubiquitous, ca...

Herpesviruses Dana Koptides, PhD 31 October 2024 Herpesviruses - Outline General features of human herpesviruses Classification Replication and Structure Herpesvirus latency Pathogenesis and treatment of different human herpesvirus disorders Herpesviruses - General features Ubiquitous, causing variety of diseases, latent infection (Herpes is for life) More than 100 herpes viruses, found in all vertebrate species, exception - oysters, host-specific 8 human herpesviruses - HSV1, HSV2, VZV, EBV, CMV, HHV6, HHV7, HHV8 Exception - Herpesvirus B - zoonotic virus - mild infection in natural host - rhesus monkey, fatal in humans All share the same morphology, replication cycle, and latency and recurrent infection Cell mediated immunity is a key in control - increased risk for any group with compromised immunity  Herpesvirus infection Primary infection - virus replication, generally mild symptoms, rapidly resolved Host becomes immune for future reinfection Latent infection - maintenance of viral genomes for the lifetime, in different cell types, no infectious viral particles produced Reactivation - stress to the host cell, immunity of the host  Classification of human herpesviruses Based on: Tissue tropism Genome structure CPE Site of latency Pathogenesis and disease manifestation Herpesviruses - General characteristics Enveloped - dsDNA - large viruses DNA core surrounded by icosadeltahedral capsid Genome size - 120 - 240 kbp Encode more than 100 genes Several glycoproteins found in the envelope, for attachment, fusion and escape of immunity (have proteins that look like MHC-I molecules, pseudo IL-10) Replication strategy adapted to the immune defences of the host Sensitive to acids, solvents, detergents, and to drying  Replication of herpesviruses Herpes Simplex Virus (HSV) Prototype herpesvirus, HSV1 and HSV2 very similar 150 nm in size HSV virion Linear dsDNA Capsid - 15-20 proteins, major protein UL19 or VP5, (12 pentameric and 150 hexameric capsomers) Matrix - tegument, at least 15 proteins (VP16, vhs - virion host shut-off protein) Envelope - lipid bilayer of cellular origin and more than 10 viral glycoproteins  HSV genome 152.000 bp long, linear in the virion, circular during replication in the host cell Encodes nearly 100 transcripts and 70 ORF, splicing uncommon Encode most of the enzymes to increase pool of nucleotides in the cell (thymidine kinase, ribonucleotide reductase, uracil DNA glycosylase, deoxyuridine triphosphatase), viral DNA polymerase 50% of HSV1 genes are not required for replication in cell culture (“dispensable”), involved in latency or evading host immune system HSV genome organization UL US a - ends of linear molecule, DNA circularization, viral DNA packaging signals TRL, IRL - Long repeat regions, terminal, internal UL - Unique long region US - Unique short region TRS, IRS - Short repeat regions 3 origins of replications - oriL is in the middle of the UL region; oriS is in the RS, and thus is present in two copies Genome organization, other herpesviruses HSV-1 Genetic map Viral entry Infection of epithelial cells 5 viral envelope glycoproteins participate in the entry - gB, gC, gD, gH and gL Cellular binding receptor - Heparan sulfate Cellular entry receptors - TNFRS14 (tumor necrosis factor receptor - type of glucosaminoglycan) or nectin-1 and nectin-2 (cellular adhesion) viral gB or gC attach to heparan sulfate, which facilitates binding of gD to TNFRS14 Membrane fusion - gB, gD, gH-gL and gD receptor (see next slide for illustration) Capsid and tegument protein VP16 transported along cellular microtubules to the nucleus Tegument protein vhs (viral shut-off protein) remains in cytoplasm - reduce cellular replication HSV productive infection - Transcription initiation Viral DNA nuclear entry + VP16 VP16 activates the immediate-early (α) genes (DNA binding proteins, transcription regulation) VP16, or α-TIF (alpha-transinducing factor), interacts with cellular Oct1 (octamer-binding protein), which binds to the IE promoter to a specific sequence to initiate transcription Progressive cascade of gene expression HSV gene expression Three classes of viral genes: immediate-early (α) - regulatory genes involved in mobilizing cellular transcriptional machinery, no DNA replication (ICP4, ICP0, ICP27/UL54, ICP22/US1, ICP47/US12) early (β) - genes involved in viral DNA replication: DNA polymerase (UL30), DNA-binding proteins (UL42 and UL29), ori-binding protein (UL9), and the helicase–primase complex (UL5, -8, and -52). late (γ) - viral structural proteins (more than 30 HSV-1 gene products are structural components of the virion) Sequential cascade of gene expression Transcription occurs in nucleus, host’s RNA polymerase II mRNAs transported to cytoplasm for translation Transport of proteins back to nucleus Late proteins glycosylated in Golgi and attached to nuclear membrane DNA concatemers cleaved and packaged to nucleocapsids transport to cytoplasm - budding Herpesvirus genome replication At least 7 virus-coded proteins are necessary for replication Viral DNA replication - viral UL9 protein binds to one of the 3 origins of replication DNA unwinding - UL9 and UL29 -viral single-stranded DNA binding protein Helicase/primase complex (UL5, UL8 and UL52) - RNA primers synthesis UL30 (viral DNA polymerase)+UL42 -> DNA synthesis Source: http://darwin.bio.uci.edu/~faculty/wagner/hsv4f.html Nucleocapsid assembly Capsid assembly in nucleus: DNA + major capsid protein VP5 arranged in pentons and hexons - nucleocapsid Glycoproteins: - gathered on inner membrane of nucleus (and in cytoplasm) the viral nucleocapsid is enveloped by the nuclear membrane that translocates the nucleocapsid to the cytoplasm Virus envelopment and budding Double envelopment process Virion assembly - Double envelopment process Nucleocapsid de-enveloped Tegument proteins VP16 and vhs are added The final envelope is acquired by budding into the glycoprotein-containing Golgi-derived vesicles Latency of herpesviruses Lytic infection - cell death All HHVs have developed tactics to remain in latency in the host - infection for life General properties of latent infections: - viral gene products of productive replication are not created or in very low concentrations - cells harboring the latent viral genome are poorly recognized by the immune system - viral genome persists intact so that productive infection can be initiated to spread infection to new hosts Human Herpesviruses - 3 groups Alphaherpesviruses (HSV1, HSV2, VZV) Betaherpesviruses (CMV, HHV6, HHV7) Gammaherpesviruses (EBV, HHV8) Alphaherpesviruses Virus Primary target Latency Transmission Disease cell Herpes Simplex 1 Mucoepithelial Neurons Close contact Cold sores, HSV-1 (HHV1) cells (kissing, sexual genital sores contact) Encephalitis Herpes Simplex 2 Mucoepithelial Neurons Close contact genital sores HSV-2 (HHV2) cells (sexual contact, Encephalitis kissing) Varicella Zoster Mucoepithelial Neurons Respiratory and Chickenpox Virus VZV (HHV3) and T cells close contact Shingles (zoster) HSV-1 - Establishing latency Prevalence >70% Viral particles created in epithelial cells, infect other types of cells (dendritic cells, natural killer cells) - spread infection to nerve terminals of neurons Site of latency - trigeminal ganglia: multiple copies of viral DNA remain in nucleus only very limited transcription occurs no further replication is needed to persist - neurons do not divide Ganglia are clusters of nerve cell bodies found throughout the body. They are part of the peripheral nervous system and carry nerve signals to and from the central nervous system Latency Associated Transcript (LAT) Only LAT and miRNAs expressed during HSV latency LAT is expressed only in latently infected neurons LAT contains 2 ORFs, no translation occurs LAT RNA may have activity of silencing to maintain viral genome in latent state LAT is necessary to maintain latency but also for the virus to be reactivated HSV-1 infection Primary infection - epithelial cells host immunity limits the infection virions spread to neighboring epithelial cells, immune cells, deeper dermis tissue virion released in close proximity to sensory nerve endings of sensory or sympathetic nerve Latent infection of ganglia is established - possible reactivation Rarely, the nucleocapsid can travel to the CNS - encephalitis HSV-1 Reactivation necessary for spreading virus to other hosts usually under certain stress conditions (UV light, steroids, stress) the virus replication starts and is transported via axons back to epithelial cells 2 obstacles - host is already immune and must shed viral particles to spread infection Evidence of viral mechanism to ensure immune viral response is much slower than shedding of virus - evidence of ICP47 protein inhibits MHC class I viral peptides presentation to T cells and thus delaying the immune response reactivation - blisters may occur, not always; frequency varies widely HSV-2 Usually called genital herpes, causing genital ulcers, but also encephalitis and meningitis (neonates) Prevalence 90% Primary infection - Skin rash - vesicles harboring viral particles - aerosols - transmission respiratory route Infection of respiratory epithelial cells - tonsil - T-cells - blood viremia - skin -rash Long incubation period - slow spread - cell to cell, no lytic infection, viral particles closed in cytoplasmic endosomes (fusion of cells - syncytia) Only outer skin epithelial cells - true lytic infection and spread VZV clinical features Adults more severe primary infection than children (strong immune response) Pregnancy - congenital birth defects Adults - Zoster or shingles at reactivation (10-20%, rises with age), lasts months Latency - dorsal root (spine) or cranial nerve ganglia, several viral RNAs and proteins produced Treatment - acyclovir, less efficient Prevention - Vaccines - Primary infection vaccine - children, adults with no Abs Zoster (Shingles) vaccine - adults above 50 - 60 years Betaherpesviruses Virus Primary target Latency Transmission Disease cell Monocytes, monocytes, Close contact Mononucleosis granulocytes, myeloid stem Transfusion, Congenital Cytomegalovirus lymphocytes, cells Tissue transplant disease CMV (HHV5) Immunosuppre epithelial cells Congenital sed Human Lymphocytes, T cells Saliva Roseola Herpesvirus 6 skin? (HHV6) Human Lymphocytes, T cells Saliva Roseola Herpesvirus 7 skin? (HHV7) Cytomegalovirus CMV - Very ubiquitous, >90% 80-year olds are Abs+ - Common infection in childhood (30% 3-year olds in daycare shedding the virus…) often asymptomatic, easy transmission - direct contact or fomites - shedding in saliva, urine, sexual contact, breast milk… organ donation and blood transfusion - Primary Infection - upper respiratory or gastrointestinal route, infecting lymphocytes - dissemination throughout the body, infecting different tissues/organs, mostly asymptomatic - Latency - in myeloid progenitors in the bone marrow (precursors of macrophages, monocytes, dendritic cells) Hiding in the immune system (great in evasion) CMV clinical features 1. Infectious mononucleosis (10% of cases, caused mostly by EBV) 2. Congenital CMV syndrome (CMV seronegative pregnant women infected during pregnancy, baby is at risk for developing CMV complications - hearing loss, visual impairment, mental and motor problems) 3. Opportunistic pathogen in immunocompromised patients (infectious mononucleosis, pneumonia, hepatitis in transplant patients, retinitis in AIDS patients) The most important post-transplant viral infection, causing many problems - clinical disease, transplant rejection Treatment - ganciclovir - inhibition of viral DNA polymerase (guanosin analog) - no vaccine HHV-6 and HHV-7 - Closely related - Causing a skin condition in infants/small children known as exanthema subitum (roseola), high fever - High prevalence (80-95%) - Latency in T-cells (HHV6 DNA integrates) Gammaherpesviruses Virus Primary Latency Transmission Disease target cell B cells, B cells Saliva (kissing Infectious Epstein-Barr epithelial cells disease) mononucleosis, Virus EBV Cold symptoms (HHV4) Cancer of B- cells B cells, B cells, Close contact Kaposi Kaposi epithelial cells epithelial cells (STI), maybe Sarcoma Sarcoma virus saliva, low Castleman’s KSHV (HHV8) transmission disease rates Epstein-Barr Virus (EBV) Most common herpesvirus, high percentage (95%) of adults have antibodies to EBV Lymphotropic virus, infects both epithelial cells and B-lymphocytes The virus is able to persist in a latent state for the life of the host in B-cells Transmission - saliva (‘kissing disease’) - from a person shedding virus asymptomatically EBV infection Primary infection - often mild in children - mild fever, pharyngitis, lymphadenopathy main cause of infectious mononucleosis (mononuclear cells in blood - WBC with non-segmented nucleus - lympho- and monocytes) in adolescents and young adults IM symptoms - fever, pharyngitis, lymphadenopathy, fatigue Reactivation of EBV - common, often asymptomatic shedding in saliva Cancers - Burkitt’s lymphoma, nasopharyngeal carcinoma, etc  EBV Latency After primary infection, small subset of infected B-cells escapes the immune system Latency is maintained in a cell that is relatively short-lived (B lymphocyte) - need for blocking of apoptosis and for proliferation No virion production - EBV genome in circular form in the nucleus - episome - copied by cellular DNA polymerase EBV latency transcripts Initial stages of latency in B lymphocytes - expression of a number of transcripts: - Six transcripts encoding six separate Epstein–Barr nuclear antigens (EBNA) - Three transcripts encoding latent membrane proteins (LMP) - Small non-coding RNAs (EBER - Epstein-Barr encoded RNAs)  3 stages of EBV latency Depending on Latency stage - change in B cell behaviour Naive B-cell EBV infection - Latency 3 - B cell activation and becomes a proliferating cell Latency 2 - restricted transcription - differentiation to memory B cell Latency 1 - further restriction in gene expression - EBNA-1 allows for EBV genome replication with the B cell division - limited gene expression - T-cell immune response escape EBV reactivation Requires specific stimulation of the latently infected lymphocytes - differentiation of B memory cells into plasma cells - close contact with epithelial cells EBV inhibits cell-based interferon defenses by the expression EBERs Latent EBV infection - increased tumor risk - oncogenesis is a byproduct of EBV latency - transient induction of proliferation of B-lymphocytes from resting state into active cell and back to resting No specific treatment, no vaccine HHV 8 (KSHV) Discovered in 1994 Kaposi sarcoma-associated herpesvirus (KSHV) KS described in elderly men of mediterranean origin in late 19th century (purple lesions on the skin), Epidemic of lesions among young men in 1980s - AIDS KS - cancer starts in lining of blood and lymph vessels Castleman’s disease - disease of lymph nodes and lymphoid tissue Diagnosis of herpesvirus infection Antibodies - ELISA IgM - primary infection IgG - previous infection - detectable for life Viral DNA detection - PCR Cell culture - CPE Herpesviruses - Summary Characteristics of all herpesvirus - Large dsDNA viruses - Icosahedral capsid, tegument between capsid and envelope - Encode vast array of proteins - Sequential cascade of gene expression - Establish latency with minimal gene expression, reactivation - Very common, easy transmission, mostly non-threatening diseases