L-11 EBV PDF

MMED3939: EBV August 30th 2024 EBV – Discovery – Diseases – The virus – Replication – Latency – Immune responses, immune evasion – Note to self: Don’t forget to record it! But first: what do you know about EBV?  But first: what do you know about EBV? What sort o...

MMED3939: EBV August 30th 2024 EBV – Discovery – Diseases – The virus – Replication – Latency – Immune responses, immune evasion – Note to self: Don’t forget to record it! But first: what do you know about EBV?  But first: what do you know about EBV? What sort of virus is it? – Implications? How is it spread? Do many people have it? What cell types does it replicate in? Does it have a latent phase, if so, where? What about the immune response to EBV? – Innate vs adaptive? Does it evade the immune system? – If so, how?  Epstein-Barr virus Credit for the discovery should go to Dennis Burkitt, 1911-1993 Burkitt’s lymphoma: common in African infants  Burkitt’s Research. The Medical Research Council provided a grant of £25. Burkitt spent this on postage stamps: he sent postcards to clinics around Africa asking them about the incidence of tumors Dennis Burkitt’s African lymphoma belt. Distribution of Malaria in Africa  Lymphoma and malaria What is the link between malaria and Burkitt’s? Does malaria cause Burkitt’s lymphoma?? No, but malaria powerfully suppresses T-cell functions in infant children – More on T cells later  EBV discovery Electron microscope examination of African lymphoma tissue samples, by Tony Epstein and Yvonne Barr, showed a Images: wikipedia herpes virus. Werner and Gertrude Henle found the same virus causes “glandular fever” in the first world. A technician in their lab had glandular fever and was found to have seroconverted for EBV.  EBV A herpesvirus: dsDNA, about 192kb, 85 genes. Images: wikipedia  Other EBV-linked diseases The most common disease caused by EBV is an acute infection in infants. – In the first 1-2 years of life, most kids get lots of bugs, causing rashes, fever and irritability. – EBV is one such cause – >50% of people catch EBV this way  Other EBV-linked diseases Very common is infectious mononucleosis, or glandular fever. – Fever, sore throat, enlarged lymph nodes, fatigue, which can last weeks or months. – Often seen in teenagers – Less common than acquisition in childhood Primary EBV infection is “self-limiting”: – The symptoms usually go away by themselves  How common is EBV? >90% of the adult population carries EBV Two peak ages of acquisition: – Most commonly caught in childhood – If not, often in adolescence, for me in 1977  Are there any interventions? Vaccines? None that work. – gp350 is said to be a vaccine candidate Antivirals? None that work well. Treatment of infectious mononucleosis is “supportive”.  Viruses and cancer Viruses are thought to cause >10% of the world’s ca. 1.3 x 107 new cancer cases each year. About 500,000 due to high-risk HPVs. A similar number from HBV + HCV. EBV causes >200,000 new cancer cases/year. Shannon-Lowe and Rickinson, Frontiers in Oncology 2019.  EBV-linked tumors of the immunocompromised host B-cell lymphomas of congenitally immunodeficient children Posttransplant lymphoproliferative disease (PTLD) B-cell lymphomas of patients with AIDS Smooth muscle cell tumors  EBV-related tumors post-transplant lymphoproliferative disorder (80- 90%) Hodgkin’s lymphoma (20-80% association) T-Cell and natural killer cell lymphomas (100% association) Nasopharyngeal carcinoma (30-100% assoc.) Gastric carcinoma (15-100% assoc.) Leiomyosarcoma (100%) Burkitt’s lymphoma (20-85% association) Oral hairy leukoplakia: an epithelial cell proliferation Associated with EBV and HIV-caused immunosuppression  How can we study EBV? No good animal model LCLs: lymphoblastoid cell lines, derived from B cells Draw blood from a person, remove & discard red cells and plasma Add EBV to the white cells and culture The colonies of cells that grow out after 2- 3 weeks are EBV-transformed LCLs Sometimes can spontaneously grow out of a sample of white cells because of endogenous EBV  EBV attachment and entry B cells: viral gp350 binds CD21, then gp42 binds MHC class II molecules HLA-DR, -DP or -DQ, triggering fusion. Epithelial cells: viral BMRF-2 binds cellular β1 integrins, then viral gH/gL complex binds αvβ6/8 integrins, triggering fusion T cells: probably a similar mechanism to B cells – Smith et al J Virol 2020 With a large DNA genome, it’s got room for lots of genes.  Immune responses to EBV by: – innate immunity – Adaptive immunity.  Innate immune responses to EBV Toll-like receptors: a family of highly conserved membrane-spanning, pattern-receptive molecules that signal in response to binding their ligand (gp350?) Image: wikipedia  Innate immune responses to EBV TLR activation leads to mobilization of many features of innate immunity, eg. IFN expression, activation of NK cells and inflammatory cytokines Image: wikipedia  Adaptive immune responses to EBV During acute phase of EBV, up to 80% of all circulating T cells are specific for EBV antigens A dramatic increase in EBV-specific CD8 T cells, and a large increase in CD4 T cells This decreases with resolution of the disease but even in healthy EBV carriers, 5-10% of T cells are specific for EBV antigens –one of the single most prominent groups of T cells  Adaptive immune responses to EBV Intense antibody response: – Prompt IgM, durable IgG Previous EBV infection is readily detected by antibody tests.  Lytic vs latent infection Lytic infection occurs in epithelial cells of the oropharynx, ie, around the mouth Latency is in B cells – Lytic infection probably happens in B cells as well. The proportion of infected B cells during acute infection is ~ 1/1000, during latency ~1 in a million  EBV replication In productive, lytic infection, viral DNA polymerase replicates the viral genome In latency, EBV replicates to a lower level but it must still replicate because as the host cells divide, both daughter cells inherit an EBV genome. Viral replication in latency uses host DNA polymerase. How does it manage the switch?? EBV genes expressed in LCLs: B cells bearing the virus in vitro. The Epstein-Barr nuclear antigens (EBNAs) LMPs (latent membrane proteins) EBERS (EBV-encoded small RNA molecules) Figure: Fields Virology  Multiple forms of EBV latency in LCLs Source: wikipedia EBV-linked tumours and lymphoproliferative diseases display a variety of the above forms of latency -Shannon-Lowe and Rickinson, Front. Oncol. 2019. It’s not easy to tell which EBV genes cause cancer!  EBNA-1 tethers viral genomes to cellular chromosomes, ensuring that at cell division, each daughter cell has viral genomes strongly up-regulates transcription from some cellular genes when expressed in a cell data regarding its role in oncogenesis is confusing.  EBNA-2 essential for B cell transformation in vitro strongly up-regulates transcription from many cellular genes, including c-myc, c-fgr and other genes involved in growth  Immune evasion by EBV Expression of only a few genes during latency Effect on innate immunity – Turning off apoptosis – Blocking action of IFN and other innate systems – Poorly understood Effect on adaptive immunity – Blocking of signalling in B cells  EBERs: blocking innate immunity A family of molecules, EBER1 and EBER2 are the most abundant viral transcripts, up to 107 copies/cell Uncapped, polyA-, non-coding, non-translated RNAs of 167 and 172 nucleotides Form extensive secondary structure Are highly conserved across different EBV isolates. Play multiple roles in EBV-bearing cells Form complexes with cellular protein kinases and thereby profoundly influence cell signalling in EBV-bearing cells  EBERs Bind the RNA-activated protein kinase R (PKR), blocking its phosphorylation This confers resistance to IFN-α-mediated apoptosis Also bind with TLRs  Adaptive immune evasion by EBV: LMP1 A membrane-bound protein with 6 trans- membrane domains and a cytoplasmic tail that interacts with cell signalling systems when expressed by itself has powerful transforming effects on the cell acts as a constitutively activated (“jammed on”) receptor, mimicking CD40, a member of the tumor necrosis receptor family TRADD (tumor necrosis factor activated death domain protein) turns on apoptosis, BUT NOT IF LMP1 TURNS IT ON! Activates Akt, NFκB, and Stat3 in B Cell lymphomas  Adaptive immune evasion by EBV: LMP2 12 trans-membrane domains and a cytoplasmic tail that interacts with cell signalling systems mimics a constitutively activated (“jammed on”) B cell receptor when expressed by itself does NOT appear to have powerful transforming effects on the cell Blocks apoptosis Activates lots of kinases: syk, lyn, vav, PI3-K, etc  EBV, B cells and life EBV-infected B cells are trying to kill us! – A potential tumor, struggling to get a foot-hold, in 90% of people T cells armed against EBV are keeping us alive! – One of the single largest groups of CD8 T cells!  EBV and myc in many cases of Burkitt’s, there is translocation and resultant activation of c-myc This seems to be a frequent feature of the complete extent of EBV-linked oncogenesis oncogenesis by EBV is complex, multi-factorial, and not well understood.  EBV & multiple sclerosis: a link? The causes of MS remain obscure Some epidemiologic data suggests that EBV may play a role: – Being EBV –ve protects from MS – Having had symptomatic EBV (ie infectious mononucleosis) doubles MS risk. Many other factors also increase MS risk; MS pathogenesis is likely to be multifactorial, with EBV possibly involved. Dobson and Giovannoni, Eu J Neurology 2019  EBV & breast cancer: a link? Lots of reports of detection of EBV in BC. Even more reports of BC being EBV -ve – Remember that BC is likely to be inflamed, so would contain lots of B cells. BC-derived cell lines don’t contain EBV So probably not.  questions What sort of virus is EBV? Does this have implications for its biology? How is the tropism of EBV reflected in the diseases it causes? In which tissues does EBV have a latent phase? Describe 3 key features of: – the immune response to EBV – Immune evasion by EBV  More information: Chapters 68a and 68b of Fields Virology. “Innate immune modulation in EBV infection”, S Ning, 2011, Herpesviridae 2:1 “Recognition of herpesviruses by the innate immune system”, Paludan et al, 2011 Nat. Rev. Immunol. 11:143 “Immune modulation during latent herpesvirus infection” White et al, 2011, Immunol. Rev. 245:189 “Modulation of innate immunity system by Epstein– Barr virus-encoded non-coding RNA and oncogenesis” Samanta and Takada, 2010, Cancer Sci. 2010, 101:29