Viral Pathogenesis & Antiviral DefensesViral Pathogenesis & Antiviral Defenses

Youhua Xie(谢幼华)Youhua Xie(谢幼华)

MOH&MOE Key Lab of Medical Molecular VirologySh h i M di l C ll F d U i itShanghai Medical College, Fudan University

复旦大学上海医学院

分子病毒学教育部/卫生部重点实验室分子病毒学教育部/卫生部重点实验室

yhxie@fudan.edu.cn

Only A Few Viruses Are Pathogenic to Humans

Most viruses do not infect humansMost viruses do not infect humans

Infections of many human viruses take place and proceed unnoticed, producing no diseases, p g

Non-pathogenic

Controlled by human antiviral defensesControlled by human antiviral defenses

Viral Epidemiology

Study the distribution of determinants of disease in human Study the distribution of determinants of disease in human populations

Endemic (infections present at fairly low but constant level)

Epidemic (infections occur greater than usually found in the population)

Pandemic (infections are spread worldwide)

Viral Pathogenesis

Th f d i di b i l i f tiThe process of producing diseases by viral infections

The factors that determine the development of viral diseases in the host involve complex and dynamic virus hostin the host involve complex and dynamic virus-host interactions

Disease severities are varied ranging from very mild to fatalDisease severities are varied, ranging from very mild to fatal, depending on the role of both viral and host factors in influencing viral infection and disease progression

Viral Pathogenesis

Viral transmission and entry into the host

Spread in the host (systemic or localized infections)Spread in the host (systemic or localized infections)

Tropism

Vi lVirulence

Patterns of viral infection and disease

Host factors & host defense

Viral Pathogenesis

St f P li i P th iStages of Poliovirus Pathogenesis

Common Routes of Viral Horizontal Transmission

ROUTE OF ENTRY

SOURCE/ MODE OF TRANSMISSION

EXAMPLES/VIRUSESENTRY TRANSMISSION

Respiratory Aerosol droplet inhalation Influenza virus, parainfluenza virus, respiratory syncytial virus, measles, mumps, rubella,

i ll t i h t ivaricella-zoster virus, hantavirusNose or mouth hand or object nose Common cold (rhinovirus, coronavirus,

adenovirus)Salivary Direct salivary transfer (eg kissing) Herpes simplex virus (oral labial herpes)Salivary Direct salivary transfer (eg, kissing) Herpes simplex virus (oral-labial herpes),

Epstein-Barr virus (infectious mononucleosis), cytomegalovirus

Gastrointestinal Stool hand mouth and/or stool Enteroviruses, hepatitis A virus, poliovirus, object mouth

, p , p ,rotavirus

Skin Skin discharge air respiratory tract Varicella-zoster virus, small pox virus

Skin to skin Human papilloma virus (warts)Skin to skin Human papilloma virus (warts)

Animal bite to skin Rabies virus

Blood Blood products, transfusion or Hepatitis B virus, hepatitis C virus, hepatitis D needle prick virus, human immunodeficiency virus (HIV),

human T lymphotropic virus, cytomegalovirus

Common Routes of Viral Horizontal Transmission

ROUTE OF SOURCE/ MODE OF EXAMPLES/VIRUSESENTRY TRANSMISSION

Blood Insect bite Arboviruses, dengue virus, yellow fever virus, West Nile virus, encephalitis causing arboviruses

Genital Genital secretions Hepatitis B virus, HIV, herpes simplex virus, cytomegalovirus

i i l i ( i )Urine Urine Polyomavirus (BK virus)

Eye Conjunctival Adenovirus, cytomegalovirus, herpes simplex virus 1

Zoonotic Animal bite Rabies

Arthropod bite Arboviruses

Mammals excreta Arenavirus hantavirus filovirusMammals excreta Arenavirus, hantavirus, filovirus

Chicken, wild birds–aerosol droplets

Avian influenza virus (bird flu, H5N1)

Vertical Transmission

SOURCE/ MODE OF TRANSMISSION

EXAMPLES/VIRUSESTRANSMISSIONPrepartum or transplacental Cytomegalovirus, parvovirus B19, rubella virus,

human immunodeficiency virus (HIV)I t t d i d li /bi th H titi B i h titi C i hIntrapartum or during delivery/birth Hepatitis B virus, hepatitis C virus, herpes

simplex virus, HIV, human papilloma virusPostpartum or via breast feeding Cytomegalovirus, hepatitis B virus, human T

l h t i i HIVlymphotropic virus, HIV

Major Patterns of Viral Infections

Ab ti i f ti ( i )Abortive infection (no progeny viruses)

Lytic infection

Persistent infection

Most persistent infections have an acute phase

Chronic infection (eg. HBV, HCV)

Latent infection (eg Herpesviruses)Latent infection (eg. Herpesviruses)

Slow virus infection (eg. HIV)

Vi l t f tiViral transformation

Factors Determine Viral Pathogenesis

Viral virulence (eg. cytopathic effect)

Cellular and tissue damages as a result of host antiviral defenses against viruses [eg. host defense mediated inflammation (localized or systemic]inflammation (localized or systemic]

Oncogenic factors

Viral oncogeneViral oncogene

Insertion of viral DNA in the host chromosome

Viral Virulence

The ability of a virus to cause disease in an infected hostThe ability of a virus to cause disease in an infected host (pathogenicity)

Molecular and genetic determinants of viral virulence are Molecular and genetic determinants of viral virulence are located throughout the viral genome

Different strains of the same virus may differ in the degree of virulence

Strains have mutated and lost their ability to cause cytopathic ff t (CPE) d di t d i l teffects (CPE) and disease are termed as avirulent or

attenuated strains

Multiple Layers of Antiviral Defence

Physical and chemical barriers: skin, mucous secretions, tears, low pH, etc.Physical and chemical barriers: skin, mucous secretions, tears, low pH, etc.

Intrinsic defence and innate immunity

Detection of altered cell metabolismDetection of altered cell metabolism

Detection of macromolecules made only by invading virus

A t h t ti d ti d th thAutophagy, apoptotic and necrotic death pathway

Production of cytokines, interfere with early steps of viral replication

Ad i i iAdaptive immunity

Direct, amplified response by coordinated action of cytokines and lymphocytes

Virus clearance by antibodies, helper T cells, and cytotoxic T cells

Generation and maintenance of memory B and T cells

Multiple Layers of Antiviral Defence

Physical Intrinsic AdaptiveChemical Innate

Intrinsic Antiviral Defence

Directly restricts viral replication and assembly, thereby rendering a cell nonpermissive to a specific class or species of viruses (eg TRIM5a/HIV 1)of viruses (eg. TRIM5a/HIV-1)

Confered by mostly preexistent restriction factors

May be enhanced by viral infection

CRISPR system (clustered, regularly interspaced short li d i t ) (b t i d h )palindromic repeats) (bacteria and archaea)

RNA interference (Plants, invertibrates and perhaps vertibrates)vertibrates)

Cascade of Innate and Adaptive Antiviral Immunity

Pattern recognition Not recognized

receptorNot recognized

Sentinel cells (Antigen-presenting cells)Complement

Cytokines

No innate response Innate response

Complement

Sentinel cells (Antigen-presenting cells)NK cells, complement

Cytokines

Adaptive response

Cells in the immune systemimmune system

Immunobiology 6ed

Innate Antiviral Immunity

Function without the prior exposure to virus

Acti ated ithin min tes to ho rs after infectionActivated within minutes to hours after infection

Together with intrinsic antiviral defence, are the defences available for the first few days after infectionfirst few days after infection

Composed of cytokines, sentinel cells, complement, NK cells

li i i f “ lf” f i iRelies on recognition of “non-self” pattern of virus using pattern recognition receptors

Can inform and stimulate adaptive antiviral immunityCan inform and stimulate adaptive antiviral immunity

Generalized model of viral replication cycle

Curr Opin Immunol 2007, p17

Pattern Recognition Receptors

PRR LigandMBL (mannose-binding lectin) Mannose and fucose residues

ith t iwith correct spacingScavenger receptors Anionic polymersTLR-1/TLR-2 Peptidoglycan, lipoproteins,etc./ ep dog yc , pop o e s,e c.TLR-2/TLR-6 Peptidoglycan, lipoproteins,etc.TLR-3 dsRNATLR-4 LPS, lipoteichoic acidsTLR-5 FlagellinTLR 7 RNATLR-7 ssRNATLR-8 G-rich oligonucleotidesTLR-9 Unmethylated CpG DNATLR 9 Unmethylated CpG DNANOD1, NOD2 ProteoglycansRIG-1, MDA-5, LGP2 Cytosolic viral dsRNAAIM-2, DAI, IFI16, DDX41, RNA Pol III

Cytosolic viral dsDNA

Sensing of Viral Infection by Toll-like Receptors

J. Mol. Biol. (2014) 426, 1246-64

Cytosolic Viral dsRNA Sensor Signalling Pathway

Antiviral Research 100 (2013) 615-35

Human Interferons

Type Name Producer cellsType I IFN-α (13) Most nucleatedType I IFN α (13)

IFN-βIFN-ε

Most nucleated cells

IFN-ωIFN-κ

Type II IFN-γ T cells, NK cellsType III IFN-λ (3) ?

Antiviral Functions of Interferons

Induce resistance to viral replication in cellsInduce resistance to viral replication in cells

Increase MHC class I expression and antigen presentation in cells

A ti t d d iti ll d hActivate dendritic cells and macrophages

Activate NK cells to kill virus-infected cells

Interferon Signalling Pathway

Nat Rev Immunol. 2008, 8:559

OAS(2’-5’-oligoadenylate synthetase)-RNaseL

Nat Rev Immunol. 2008, 8:559

Crosstalk between Innate and Adaptive Antiviral Immunity

CD8 T cells

Lysis of infected cellscells cells

Innnate imm

Mature DCCytokines

TH1 Activate macrophage

munity Complement

NK cells

CD4 T Activate B TH2

macrophage

cells cellsTH2

TH17 Inflammation

Dendritic Cells (DCs)

Immature DCs circulate in periphery, around body cavities, under mucosal surfacesunder mucosal surfaces

Virus-interacting DCs maturize in lymph nodes, present internalized viral protein epitopes on MHC class II tointernalized viral protein epitopes on MHC class II to lymphocytes

Link innate and adaptive immune responses

DCs can directly inhibit viral replication by producing cytokines

Activation of Naïve T Cells by DC

Cytokines

A diverse group of soluble proteins, peptides, or glycoproteins which act as immunomodulating regulators

Proinflammatory cytokines: necessary to initiate an i fl t ( it l t dinflammatory response (recruit granulocytes, and lymphocytes etc.), such as TNF-a, IL-1, IL-6, IL-12, etc.)

Anti inflammatory cytokines: serve to reduce inflammationAnti-inflammatory cytokines: serve to reduce inflammation and promote healing once the injury/infection/foreign body has been destroyed, such as IL-10, IL-4, TGF-b, etc.)

Complement System

The complement system helps or “complements” the abilityThe complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism

Circulating complement molecules are usually inactive precursors (pro-proteins). During activation, proteases in the system cleave pro proteins to initiate an amplifying cascadesystem cleave pro-proteins to initiate an amplifying cascade of further cleavages.

It can be recruited and brought into action by the adaptiveIt can be recruited and brought into action by the adaptive immune system

Natural killer cells (NK cells)

NK cells are a type of large granular, cytotoxic lymphocyteyp g g y y p y

Differentiate and mature in the bone marrow, lymph node, spleen, tonsils and thymus, and enter into the circulation

Recognize stressed cells in the absence of antibodies and MHC

Provide rapid responses to virally infected cells and respond toProvide rapid responses to virally infected cells and respond to tumor formation

Inflammatory Response

Readness heat swelling painReadness, heat, swelling, pain

Reflect the communication of innate and adaptive immunity

No inflammatory response, ineffective adaptive immune response

C t thi i ll i d t i fl tCytopathic viruses generally induce strong inflammatory response

Some viruses barely induce inflammatory responseSome viruses barely induce inflammatory response

Inflammatory response may progress out of control and cause serious clinical outcomescause serious clinical outcomes

Neutralizing Antibodies

Neutralize virus particles in blood preventing infection ofNeutralize virus particles in blood, preventing infection of cells

Mucosal neutralizing antibodies prevent virus fromMucosal neutralizing antibodies prevent virus from penetrating the mucous surface

Production of neutralizing antibodies are essential for the gsuccess of many if not all existing vaccines against virus infection

Cytotoxic T Cell

Essential for clearing most viral infections

Lysis of target cells

Transfer of cytoplasmic granules containg perforin and grazymes

Apoptosis

Non-cytolytic pathway: production of antiviral cytokines such IFN-g

T Helper Cells

Th1 cells secrete cytokines that cause naïve CD8 T cells toTh1 cells secrete cytokines that cause naïve CD8 T cells to differentiate into CTL

Th2 cells secrete cytokines that activate B cells to make antibody y y

The balance of Th1 vesus Th2 is determined by cytokine mixture

Negative regulation of immune response

Immunoregulatory cytokines: IL-10 TGF-βImmunoregulatory cytokines: IL-10, TGF-β

Inhibitory receptors: PD-1, CTLA-4, LAG-3, etc

R l t T llRegulatory T cells

Altered antigen-presenting cell: DC loss or dysfunction; Non professional APCsdysfunction; Non-professional APCs

Antiviral Immune Response

Nature Review Microbiology 2004