Immune Evasion Flashcards
Defensins
Barriers = 1st Line Defense FX - Create pores in membranes of many different bacteria, fungi & enveloped viruses DEFENSE • *Polypeptide Capsule - Blocks activity of defensins; Antiphagocytic BUG • Bacillus anthracis
Lysozyme
Barriers = 1st Line Defense
FX
- Enz in sweat, saliva, serum & tears
- breaks down peptidoglycan (AKA Murein)
DEFENSE
• G(-) bact’s outer-membrane protects them from lysozyme reaching their peptidoglycan layer
BUGS
- G(-) bact are naturally more protected than G(+) against lysozyme bc that outer-mb
Stomach:
- *Acid
- *gastric peristalsis
Barriers = 1st Line Defense
DEFENSE
• Urease to increase pH
• Motility - polar flagella and spiral shape for efficient hydrodynamic movement
• chemotaxis & adherence to gastric epithelium
BUGS
• Helicobacter pylori
Capsule
Innate I/S Defenses = 2nd Line Defense How evade Complement FX - Their polysaccharide capsules interfere with effective complement deposition on the bacterial cell surface by *binding factors that can regulate C3b. - This negates both direct complement injury by MAC complex and makes the receptors recognized by phagocytes unavailable. BUGS 1) Escherichia coli 2) Group B strep 3) Haemophilus influenzae type B 4) Klebsiella pneumoniae 5) Neisseria meningitidis 6) Salmonella 7) Strep pneumoniae
I/S COUNTERS BACK
- once Ab’s form, Ab’s directed against the capsular antigen reverses this effect bc C3b can then bind in association with IgG and lead to activation of the classical pathway of complement activation and eventually opsonization and clearance by the spleen.
BUGS COUNTER the I/S’s Counter:
─ Protein A
M protein (surface Antigen)
Innate I/S Defenses = 2nd Line Defense How evade Complement FX - Binds host cell plasma protein, fibrinogen, which interferes with the alternative pathway of complement deposition by forming a dense layer on the bacterial surface. BUGS • Group A streptococcus
Hyaluronic Acid (HA) capsule
Innate I/S Defenses = 2nd Line Defense
How evade Complement
FX
- HA great abundance in human connective tissue.
- Therefore, HA capsule = camouflaged in host antigen that does not elicit an immune response. (like a wolf in sheep’s clothing.)
BUGS
• Group A streptococcus
C5a peptidase
Innate I/S Defenses = 2nd Line Defense
How evade Complement
FX
- Enz that degrades C5a (main factor that attracts phagocytes to sites of complement deposition.)
- Thus it blocks chemotaxis of neutrophils and other phagocytes to the site of infection.
BUGS
• Group A & Group B streptococci
- *Sialylation of lipooligosaccharide (LOS) • IgA protease • Antigenic variation of pilin gene • Phase variation of opa genes • Intracellular survival
Innate I/S Defenses = 2nd Line Defense
How evade Complement
FX all
- basically camo
FX LOS
- Because sialic acid is negatively charged and a surface component of cells, camouflage and protect from the antibodies responsible for serum killing
- this modification bind serum factor H and C4b-binding protein, two negative regulators of complement activation
BUGS
• Neisseria gonorrhoeae
- Disseminated Gonococcal Infection (DGI)
Long O-antigen polysaccharide chain
Innate I/S Defenses = 2nd Line Defense How evade Complement FX - blocks MAC BUGS • “Smooth” G(-)
C5a peptidase
Innate I/S Defenses = 2nd Line Defense
How evade Phagocytosis
FX
- Complement component C5a as the attractant for the neutrophils,
- prevent recruitment of neutrophils, so in effect the neutrophils won’t cross over to find the bacteria.
- prevents Diaphedesis too.
BUGs
- Group A streptococcus and group B streptococcus
pertussis toxin (PT), and adenylate cyclase toxin (AC
Innate I/S Defenses = 2nd Line Defense How evade Phagocytosis FX - inhibit phagocyte migration • toxins = ↑cAMP to inhibitory levels = directly inhibits neutrophil motility and chemotaxis: - PT also results in lymphocytosis. BUGS - Bordetella pertussis
Leukocidins
Innate I/S Defenses = 2nd Line Defense How evade Phagocytosis FX • Kill the phagocytes BUGS - Pseudomonas aeruginosa - Staphylococci - Group A streptococci (streptolysin O) - Clostridium perfringens
Type III cytolysins (AKA “Injectosome”)
Innate I/S Defenses = 2nd Line Defense How evade Phagocytosis FX - produce proteins that are injected directly into host cells and interfere with cellular activation through a type III secretion system BUGS a) Yersiniae spp b) Shigellae
inhibit fusion of Lysosome w/Phagosome.
Innate I/S Defenses = 2nd Line Defense How evade Phagocytosis FX - Surviving phagocytosis BUGS • Mycobacterium tuberculosis • Chlamydophila psittacii • Salmonella spp. • Brucella spp. • Legionella pneumophila
Escape
Innate I/S Defenses = 2nd Line Defense How evade Phagocytosis FX - Escapes phagosome and then live intracellularly - Destroys phagosome mb and thus totally avoids lysosomal enzymes. BUGS • Shigella spp. • Listeria monoctyogenes - Protein: listeriolysin O (LLO) • Rickettsia spp.
