13 - Immunity to Bacteria Flashcards
(24 cards)
What are common PAMPs for gram positive bacteria?
Pam3, LTA
What are common PAMPs for gram negative bacteria?
LPS, lipid A
What PAMP is in a bacterial flagellum?
Flagellin
What PAMP is in bacterial DNA?
CpG DNA
What PAMP is in all bacteria?
PepG
What are the mechanisms of immune defense against extracellular bacteria?
- B cell activation via Ti antigen
- B cell activation via Td antigen
- Neutralizing antibodies
- Opsonized phagocytosis
- Toxin neutralization by antitoxin
- Complement pathways
What are the mechanisms of immune defense against intracellular bacteria?
- Neutrophil activation
- Macrophage activation
- NK cell activation
- T cell activation (gamma delta)
- CTL activation
- Th1 response and macrophage hyperactivation
- Neutralizing antibodies
Staphylococcus aureus
- Gram pos
- Extracellular
- Many clinical manifestations
- Common nosocomial infection
What is leukocidin?
S. aureus toxin that targets specific cells of the innate and adaptive immune system via receptor engagement
Toxic shock syndrome toxin-1 (TSST-1)
A superantigen
- Size of 22 kDa
- Produced by 5 to 25% of Staphylococcus aureus isolates
- It causes toxic shock syndrome (TSS) by stimulating the release of large amounts of interleukin-1, interleukin-2 and tumour necrosis factor
How does S. aureus evade the immune system?
- Kills host cells
- S. aureus can agglutinate with fibrin which provides protection against phagocytes
- S. aureus protein A (SpA)-mediated evasion of phagocytosis
- S. aureus protein A (SpA) manipulates B cell and T cell responses
How does S. aureus protein A (SpA) cause evasion of phagocytosis?
- SpA is present on the surface of S. aureus (SA)
- SpA binds the Fab regions of the ABs
- Decrease opsonization
- Decrease phagocytosis
How does S. aureus protein A (SpA) manipulate B cell and T cell responses?
- Induces B cell expansion then causes those cells to undergo apoptosis
- Binds to plasmablasts which causes non-specific activation and irrelevant antibodies are formed
- T cell expansion and anergy and causing cytokine storm
What does S. aureus aureolysin do?
- inhibits neutrophil chemotaxis
- inhibits neutrophil function
- cleaves antibodies
- neutralizes antibacterial peptide
- compromises opsonization
Staphyloxanthin is…
a pigment thathas anti-oxidant function that protects against oxidative
radicals
What does catalase do?
Neutralizes ROS
Listeria monocytogenes
Found in moist environments, soil, water, decaying vegetation and animals, and
can survive and even grow under refrigeration and other food preservation measures
What happens when L. monocytogenes is taken up by phagocytes?
- About 10% of the bacteria rupture the phagosome by the action of listeriolysin-O
- Bacteria replicate quickly in the cytoplasm
- The host cell pushes the bacteria through the cytoplasm toward neighbouring cells with actin
(occasionally resulting in pseudopod-
like structures that are fused with
neighboring cells)
How does L. monocytogenes evade the immune system?
- Bacterial surface protein InlB protects infected monocytes from killing by CD8+ T cells
- Increase the life span of infected monocytes
- Ensures neurovirulence
What temperature is best for L. monocytogenes motility?
The bacterium is optimally motile at 25C and less motile at body temperature
Mycobacterium bovis
- Non-motile, rod-shaped bacteria
- Obligate aerobe
- Facultative intracellular parasite
- Slow growing (15-20 hour of generation)
- Acid-fast staining
- Extensive lipid cell wall
How do tuberculosis granulomas form?
- Mycobacterium infects macrophages (Mφ) and multiply
- Recruitment of further Mφ and dissemination
- Granulomas are formed
- CD4+ & CD8+ T cells are recruited to form a rim
- The granuloma becomes necrotic
- The granuloma ruptures and viable
bacilli are released into the alveolar space
How does Mycobacterium species evade the immune system?
- Arrest of phagosome–lysosome fusion
- Resistance against reactive nitrogen species
- Interference with antigen presentation
Granulomas are the characteristic feature of…
latent pulmonary TB.
Granulomas are formed when innate and adaptive immune responses are not able to rapidly eliminate the pathogen.
Immune cells and cytokines accumulate around infected cells to control the spread of infection.
