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Microbiology And Immunology > Microbial immune evasion mechanism > Flashcards

Microbial immune evasion mechanism Flashcards

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Biology 101 flashcards
1
Q

Balance between microbe and host
State the properties involved in the balance of pathogenecity between the microbe and the host?

A
  • Pathogenecity = Capacity of pathogen to infect + cause disease
  • Microbe + host properties balance - clinical course of disease
  • Microbe (pathogenic) -> adhesions, toxins + capsule
  • Host (defensive) -> Natural barriers, defensive cells, antibacterial peptides, I + A immunity
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2
Q

Virulence factors
State the 3 purposes of virulence factors?

A
  • Virulence factors are the molecules that assist the bacterium to colonize the host at the cellular level
  • Increase colonisation + adhesion (infection establishment via adhesins)
  • Evade host defences
  • Increase tissue damage (growth via toxins)
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3
Q

Elements of the immune system evaded by pathogens
What aspect of immunity have pathogens evolved to overcome or avoid?

A
  • Natural defences (mucosal layers, skin)
  • Innate immunity (complement system, macrophages)
  • Adaptive Immunity (antigen specific and memory AB T cells -> CD4 H + CD8 CT -> via pathogen diversity + multiple immune evasion strategies
  • Pathogen diversity: Multiple immune evasion strategies
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4
Q

Innate immunity- Complement system
Very nice summary of the complement system (DNL)

A

VD

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5
Q

State ways in which negative binding failed to be triggered in the complement system?

A

LPS OR capsules, coating with non-fixing IgA -> Capsule blocks C3b binding -> Capsule prevents C3b receptor access

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6
Q

State ways in which disrupted regulation/ block MAC occurs in the complement system?

A

Factor H sequestration, C5a proteases, blebbing

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7
Q

State the 6 roles of the complement system?

A
  • Induces IF response
  • Increase chemotaxis
  • Increase phagocytosis by opsonisation
  • Increase vascular permeability
  • Mast cell degranulation
  • Lysis of cell membranes
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8
Q

State 3 examples of intracellular pathogens?

A
  • Mycobacterium tuberculosis
  • Listeria
  • Salmonella
  • Hidden from serum killing, complement + AB
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9
Q

How do bacteria prevent phagocytosis from occuring with examples?

A
  • Kill cells (via leucocidins - staphs), prevent opsonisation + block contact
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10
Q

How do bacteria survive inside macrophages + polymorphonuclear?

A

Protein A (binds Fc portion of IgG - staphs), capsules (meningococcus, Hib)

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11
Q

State 5 ways with examples of bacteria which aid intracellular pathogens?

A
  • Increase own safe uptake (CR3, mannose lectin receptors)
  • Preps cell for invasion (shigella)
  • Inhibit phagosome-lysosome fusion (M.tuberculosis)
  • Escape P-L to cytoplasm (listeria)
  • Resist oxidative killing (via catalases/peroxidases)
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12
Q

State 7 mechanisms which enable life inside macrophages?

A
  1. Directs phagocytosis via CR3 - no ROI - Reactive O2 Species
  2. Actin rearrangement - +ve engulfmant
  3. Type 3 secretion systems - prepares cell
  4. Resists digestion and ROls in PLs - SOD, catalase
  5. Escape into cytoplasm e.g. Listeria - Before lysosome fusion so doesn’t get acidified
  6. Inhibits PL fusion maintains early endosome -> Blocks acidification e.g. mycobacteria
  7. Controls antigen presentation Stops CTLs or P Lactivation -> presents decoy
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13
Q

Adaptive immunity
Describe how microbes can evade from adaptive immunity?

A
  • Concealment of antigen
  • Immunosuppression
  • Antigenic variation
  • Establishment of persistance/latency/reactivation
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14
Q

Describe the concealment of antigens

A
  • COA: Hide inside cells
  • Privileged sites
  • Block MHC antigen presentation (herpes interfes TAP protein)
  • Surface uptake of host molecules (CMV + beta-2 microglobulin)
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15
Q

Describe immunosuppression

A

Immunosuppression
- Decrease MHC
- Decrease receptors
- Stops apoptosis
- Cytokine switch
- IgA proteases

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16
Q

Mechanisms of immune evasion
Describe 4 mechanisms in how viral immune evasion can occur + examples of diseases that use for these for each one?

A
  • IC pathogens: Require adaptive cell mediated immunity
  • Latency (VZV, herpes simplex)
  • Decreases antigenic presentation (binds TAP -> inhibits peptide transfer to MHC - HS)
  • Decreased MCH expression (CMV)
  • Mutation of epitopes (B cells - neutralisation escape, T cells - CD8+ escape mutants of HIV))
17
Q

Paradigms of immune evasion + examples - Streptococcous pneumonia
State the pathogenic effects + causes from Streptococcous pneumonia? VD

A
  • Effects: Colonisation, by-pass defences, survival + damage
  • Causes: Pneumonia, otitis media (IF), meningitis
18
Q

VZV + herpes simplex
Describe how varicella-zoster virus uses persistance as an immune evasion strategy?

A

Microbes infects susceptibles -> Remains latent -> reactivates (zoster) + infects next generation of susceptibles

19
Q

Antigenic variation - definitions
State the type of phenotypes that changes occur in when antigenic variation arises?

A
  • Colony morphology
  • Virulence
  • Serotype
  • Loose flagella
  • Change surface sugars
20
Q

Define antigen diversity polymorphism?

A

Genetically stable and alternative forms of an antigen in a population of microbes

21
Q

Define antigenic variation?

A

Successive expression of alternative forms of an antigen in a specific clone or its progeny

22
Q

What is phase variation and when does it occur?

A
  • Bacteria undergo frequent and reversible phenotypic changes resulting from genetic alterations in specific loci of their genomes
  • ON/OFF of an antigen at low frequency
  • Occurs during infection OR spread of microbe through a communitv
23
Q

Describe how neisseria gonorrohoea uses variation to avoid immune response?

A
  • Surface components interact with host cells -> cell surface components undergo Phase + antigenic variation at increased frequency -> avoids immune response
24
Q

Influenza virus
Describe how influenza virus has the potential for variation?

A
  • Antigenic drift -> point mutation + immune selection
  • Antigenic shift -> gene reassortment

Microbiology And Immunology (32 decks)

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