Mechanisms of Viral Infection Flashcards
How can some bacteria evade complement?
Bacteria can resist complement:
LPS and capsules = failure to trigger complement as complement cannot bind
Negative binding: coat self with IgA that doesn’t fix complement, factor H sequestration + blockage of C3b binding
Block/expel MAC: capsule prevent C3b receptor access, C5a proteases prevent it forming
How do staphs and meningoccoccus evade the immune system?
Staphs produce leukocidins which prevent opsonisation and thus efficient phagocytosis
Also produce protein A (binds Fc portion of IgG, preventing opsonisation)
Meningococcus and Hib block contact w immune cells using capsules
Give other examples of ways in which intracellular pathogens which evade the immune system
mTB, listeria and salmonella, Shigella
Intracellular pathogens e.g. mTB, listeria and salmonella can survive inside macrophages: Promote own safe uptake- mediated by CR3 and mannose lectin receptors
Shigella injects molecules which preps cell for invasion
Listeria escapes phagosome-lysosome to cytoplasm
Resist oxidative killing by producing catalases/ peroxidases
Controls Ag presentation: Stops CTLs and cell activation
How can certain microbes mess with Ab binding?
Production of Fc receptors by microbes = antibodies bind the wrong way = not opsonised properly
Staphs, Streps, HSV, VZV, CMV
How can certain microbes cause antigen concealment?
Concealment of antigen by:
1. hiding inside cells and not get recognised
2. Infecting privileged sites where hay little migration of leukocytes, eg eyes
3. Block MHC presentation, by messing w TAP eg Herpes
4. Surface uptake of host molecules: eg CMV takes up host b2microglobulin and incorporates it into their own cell surface to avoid detection
Give the 3 other ways in which microbes can evade the adaptive!!! immune system
Immunosuppression
e.g. by decreasing MHC, receptors, apoptosis, cytokine switch, IgA proteases
Antigenic variation- mutations can avoid immunity in the community
Persistence/latency/reactivation
Describe the pathogenic mechanisms of Strep Pneumo
What does it cause, how is it transmitted, what does it release?
Gram + causes pneumonia, otitis media and meningitis
Transmitted via aerosol, enters nasopharynx and colonises
Release adhesins to bind surface molecules
Release sIgA proteases to break down IgA
Endothelial cell damage–> pneumonia, bacteria can access blood = bacteraemia-> Septicaemia and meningitis
How does strep pnemonia evade lung defences?
Inhaled in lungs and evades lung defences by:
-sIgA proteases
-Capsules which prevent phagocytosis
-Pneumolysin (toxin causes lysis of epithelial surfaces)
-Teichoic acids= bad inflammation
What are 4 ways in which VIRUSES can evade the immune system?
- Latency: VZV, herpes simplex
- Decreases MHC expression: Cytomegalovirus (CMV)
- Decrease Ag presentation/cause concealment by binding to TAP Eg= herpes simplex
- Mutation of epitopes: HIV can mutate its epitopes to escape neutralizing Abs or to avoid recognition by CD8+ T cells
Describe Persistence as an immune evasion strategy using VZV
What is antigenic diversity? Give an example
Antigenic Diversity/ polymorphisms: genetically stable and alternative forms of Ags in a population of microbes
e.g. serotypes of Strep.pneumoniae
What is antigenic variation?
Antigenic Variation: Pathogens can change their surface Ags to evade the host’s immune system. They can switch between different Ag forms w/in a specific clone or its progeny.
Phase Variation: Microbes can reversibly switch Ag expression at a low frequency. This ON/OFF Ag system allows them to evade the immune response during infection or spread through a community.
What are the symptoms of gonorrhoea?
Describe how Neisseria Gonorrhoea has antigenic variation
Gram neg coccus causes inflammatory, myogenic infection
Symptoms: dysuria, redness, pain on urination, destruction mucosa
Neisseria Gonorrhoea has v variable structures + can undergo phase and antigenic variation.
This confuses/avoids immune responses.
