Microbial Immune Envasion Mechanisms Flashcards
What are the two factors that determine balanced pathogenicity?
Properties of the microbe (pathogenic mechanisms)
- adhesins
- toxins
- capsule
Properties of the host (defensive mechanisms)
- natural barriers
- defensive cells
- antibacterial peptides
- innate and adaptive June response
What are the function o virulence factors?
Evade host defences
Promote colonisation and adhesion
Promote tissue damage
What aspects of immunity have pathogen evolved t overcome or avoid?
Natural defences - mucosal layers no skin
Innate immunity - complement system and macrophages
Adaptive immunity - antigen specific and memory antibodies T cells
What are the roles of complement in innate immunity?
Induces inflammatory response
Promotes chemotaxis
Increase phagocytosis by opsonisation
Increase vascular permeability
Mast cell degranulation
Lysis of cell membranes
How can the compliment cause microbial immune evasion?
Faliure to trigger negative binding
- LPS, capsules
- coating with non-fixing igA
- capsule blocks C3b binding
- capsule prevents C3b receptor access
Disrupt regulation block/expel MAC
- factor H sequestration
- C5 proteases, blebbing
Describe the mechanism that enables bacterial life inside macrophages
- Direct phagocytosis via CR3
- Actin rearrangement - +ve engulfmant
- Type 3 secretion systems - prepares cell
- Resists digestion and ROIs in PLs - SOD, catalyse
- Escape into cytoplasm
- Inhibits PL fusion maintains early endsome blocks acidification
- Controls antigen presentation stops CTLs
Describe the production of Fc receptors by microbes leading to antibody inhibition
Normally antibodies bbind to the microbial antigen and fuse elimination to occur
With microbial Fc receptors, the. Antibody binds but blocks specific antibody’s from binding to surface antigens on microbials
Preventing antibody binding
How can the adaptive immune system be evaded?
Concealment of antigen
- hide inside cells
- privalidged sites
- block MHC antigen presentation
- surface uptake of most molecules
Immunosuppression
Antigen variation
Persistence/latency/reactivation
What are the pathogenic mechanisms of streptococcus pneumoniae?
Colonisation
By-pass defence
Survival
Damage
What diseases are caused by streptococcus pneumonia?
Pneumonia
Otitis media
Meningitis
Describe the pathogenic mechanism of streptococcus pneumonia
- Colonisation of nasopharynx (slg4 proteases)
- Inhalation into lungs
- By-passes defences: surfactants (slg4 proteases)
- Reaches lung
- Escapes phagocytosis, inflammation - lung damage., damage to endothelial cells
- Pneumonia
- Meningitis (inflammation) and septicaemia (toxic shock).
What are ways the Viruses can evade the immune system?
- Latency
- Decreased antigenic presentation
- by binding to TAP it inhibits transfer to MHC - Decreased MHC expression
- Mutation of epitopes
B cells - escape neutralisation
T cells - CB8+ escape mutants of HIV
Describe what occurs during persistence (an immune evasion strategy)
- A small community of microbes infects susceptibles
- The Microbes remains latent
- Microbes reactivates and infects next generation of susceptible
What is a example of a virus with latency?
Herpes simplex virus 1
Gets reactivated in nerves and immunologically privileged sites with poor protective immunity for reactivation
Define antigenic diversity
Genetically stable and alternative forms of antigens in a population of microbes
