Immunity to Viruses and Non-Viral Pathogens Flashcards
1
Q
What are barrier to infection and innate response
A
- Chemical and physical barriers must be breached
- Epithelial linings of skin and gut (non-specific physical barrier)
- Secretions (contain antivirals, acidic pH, enzymes, fatty acids) are often toxic to pathogens
- Presence of normal microbiota make an inhospitable environment
2
Q
What are properties of viruses
A
- Contain DNA or RNA
- Contain a protein coat / envelope / spikes
- Infect specific types of cells in a host
- Multiply inside living cells through hijacking synthesising machinery
- Direct synthesis of viral proteins to enable replication and transmission
- Enter through surface receptors and undergo replication
- More likely to thrive if they don’t kill host
3
Q
How does the immune system respond to viruses
A
- Innate: Negotiate physical barriers, ciliated ECs, mucous / basement membranes
- Adaptive: CD4 / CD8 and B cells (effector / memory)
4
Q
What are interferons
A
- Protein released in response to the presence of viruses
- Occurs within first few hours of infection by plasmacytoid DCs
- Type 1 (IFNα, IFNβ), type II (IFNγ), type III(IFNλ1, IFNλ2, IFNλ3 = IL-29, IL-28a and IL-28b respectively)
5
Q
How are IFN-1 activated
A
- Cytoplasmic PRRs (RIG-I) detect viral ssRNA / dsRNA
- Stimulation of IRF3 and NF-kβ activation
- Transcription of IFNα and IFNβ and cytokine genes
- Plasmacytoid DCs detect virus and up-regulate type I IFN production (not infected)
- Plasmacytoid DCs take up virions and viral nucleic acids detected by TLR7 (viral ssDNA) and TLR9 (DNA containing CpG motifs) in endosomal compartments
- Stimulation of IFR7 and NF-kβ activation
- Transcription of IFNα and IFNβ and cytokine genes
6
Q
What is the role of IFN-1
A
- Interfere with viral replication
- Signal preparation of uninfected cells to resist viral infection
- Activate macrophages and NK cells to enhance antiviral activity
- Promote adaptive responses (MHC presentation)
7
Q
What are the innate mechanisms of viral immunity
A
- IFNs: Up-regulate ISGs (innate), JAK-STAT signal transduction (increased transcription of immune relevant genes)
- 2’5’ Oligoadenylate Synthetase: Activates RNaseL (targets degradation of viral RNA)
- PKR: dsRNA dependent protein kinaseR, blocks translation of viral mRNA, initiates apoptosis via Bcl-2
- Mx Proteins: GTPases that interfere with viral replication
- NO / NOS2: Potent activators of antiviral pathways
- APOBEC: Editing enzyme that inhibits infection with retroviruses, catalytic polypeptide like
8
Q
What is the role of NK cells in viral immunity
A
- Kill virally infected cells
- Maintain / increase tissue inflammation (secrete cytokines)
- Activation state regulated by activating / inhibiting receptors
9
Q
What are the effector responses to viral infection
A
- Adaptive immune response begins a few days after innate
- T cells appear at site of infection (4 days)
- CD8 are critical for resolution of viral infection
- Abs detected 6-7 days post infection, establish immunological memory
- Abs provide barrier to spread of viral infection
10
Q
What are the humoral responses to viral infection
A
- Free Virus: Antibodies block binding, entry and uncoating of virus, complement damages virus envelope / blockade of virus receptor)
- Virus Infected Cells: Complement opsonisation of virus / infected cells are phagocytosed, Ab bound attracts NK, macrophages and neutrophils
11
Q
What is the role of Th cells in viral immunity
A
- Secrete cytokines that promote antiviral activity
- IFN-y induces antiviral state in adjacent cells
- Induce hypersensitivity response (accelerated clearance)
- Activate and recruit macrophages and neutrophils to site of infection
- Induce CD8 and memory responses through IL-2
12
Q
Whats the role of cytotoxic T cells in viral immunity
A
- Actively find and destroy virally infected cells
- Prevent production of virus particles
- Kill infected cells through the release of perforin, granzymes, and other cytolytic proteins
- Trigger death through binding of TNFa or FasL ligands (signal apoptosis)
- IFNy / TNFa ‘cure’ infection through eradication of virus
13
Q
What are viral evasion strategies
A
- Impair host immune response
- Avoid recognition and resist control by effector mechanisms
- Reduce circulating pDCs / infect pDCs and impair their function
- Disrupt chemokine network (affect leukocyte migration)
14
Q
How does HIV evade the immune system
A
- Latency program
- Mutates genome rapidly avoiding presentation on MHC
- Counteracts / inhibits immune response (protein coat)
- HIV vif (counteracts APOBECS)
- HIV nef (inhibits lysis of infected cells)
15
Q
What are PRRs
A
- Pattern recognition receptors
- Activated when pathogens override epithelial barriers
- Bind PAMPs expressed on pathogens
- Bind DAMPs released by damaged cells
- Located on plasma membrane / within cytosol
- TLR, MLR, SLR
- Recognise viral RNA / DNA / proteins
16
Q
How do bacteria evade the immune system
A
- Attach host cell (proteases prevent IgA binding)
- Proliferation (surface structures) induction of apoptosis in macrophages
- Invade (secrete elastase that inactivates C3a / C5a)
- Toxin induced damage (secretion of hyaluronidase which enhances bacterial invasiveness)
17
Q
What does pathogenicity of bacteria refer to
A
- Toxicity without invasiveness
- Invasiveness without toxicity
- Combined
18
Q
What is the innate response to +ve / -ve bacteria
A
- +ve: Lipopolysaccharides activate innate, bind LPS binding protein, signal pro-inflammatory cytokine cascade
- -ve: Peptidoglycan / lipoteichoic acids recognised by TLR2
- Mycobacteria / spirochete: Lipid bilayer susceptible to lytic complex, C3a / C5a attract neutrophils, causing opsonisation / phagocytosis
19
Q
What is the humoral response to bacteria
A
- Antibody dependent anti-bacterial defences
- Antibody-Dependent cell cytotoxicity
- Opsonisation, activation of complement
- Interfere with motility of bacterial flagellin
- IgA interferes with binding of bacteria to epithelial cells
20
Q
What is malaria (parasitic infection)
A
- Protist disease caused by Plasmodium spp.
- Life cycle moves through liver / RBCs, maturational changes allow Ag shifting, intracellular phases resist Ab-based responses
- Ab responses avoided by outer coat shedding
21
Q
What is leishmaniasis (parasitic infection)
A
- Vector borne disease
- Transmitted by sandflies
- Lives in macrophage phagosomes and produces localised cutaneous self-resolving lesions and systemic visceral leishmaniasis (spleen / liver)
- Body defends via complement system, neutrophil activation, NK cells and Th1 cells
22
Q
What are helminths (parasitic infection)
A
- Parasitic worms, enter hosts via intestinal tract, exclusively extracellular
- Don’t replicate in hosts (limit immune engagement)
- Immunity may proceed via induction of IgE production and recruitment of eosinophils
- Induction of TH1 IFN-γ macrophage activation is more effective
23
Q
What are fungal infections
A
- Based on site of infection, route of acquisition and virulence
- PRRs respond and secrete antimicrobial peptides
- Induction of phagocytosis destroys fungal cells
- Capsules can prevent PRR binding and fungi-induced expulsion from macrophages
