Immunity-L3- Extracellular bacteria: Macrophages and Bacterial Evasion mechanisms-Innate I

how do phagocytes recognise pathogens?

1. opsonin dependent- CR1 recognises C3b, and Fcgamma R for antibodies

2. opsonin independent- scavenger receptors and mannose receptor

3. PRRs- TLR, NLRs etc

how do phagosome mature to phagolyososme? (4)

1. early endosome- EEA1 with low V-ATPases and not acidic

2. maturing phagosome- Rab5 GTPases down regulated, other proteins up

3. late endosome-, up regulation of LAMP1 and MHC II, increases V-ATPases

4. fuses with lysosome with AMPs- defensins, lactopherin

how are ROS/NRS made in phagocytes? (5)

1. NADPH oxidase complex assembles on the phagolyosome and coverts oxygen to superoxide O2-

2. superoxide dismutase makes H2O2

3. myeloperoxidase from the granules make HOCl- kills bacteria

NRS

1. NOS- catalyses formation of NO from L-arginine

2. NO and O2- and make ONOO- which interacts with acid- and nitrogen dioxide

apoptosis key features(4)

1. blabbing of the cell membrane

2. lipid flip of the phospholipid

3. chromatin condensation

4. DNA fragmentation- cell contents remain contained

how are neutrophils apoptoses?

1. expose phosphatidylserine on the surface as “eat me” signa

2. macrophages recognise these and they ingest it

3. macrophages produce anti-inflammatory cytokines- reducing IL-23 lowers Th-17 and stops GM-CSF to stop further neutrophil recruitment

how do bacteria evade AMPs? examples

1. proteolytic cleavage- bacteria secrete proteases that destroy AMPs

2. alter surface- reduces the negative charge of bacteria cell surface to repel positive charged AMPs

S.aureus- modifies LTA with D alanine and phospholipid with L lysine

how do bacteria evade complement? (5) with examples

1. inhibit C1q- S.aureus protein A binds this incorrectly

2. modulate C3 convertase- Staph complement inhibitor stops C3 cleavage

3. targeting C3B- roteases cleave C3b and no opsonisation

4. target C5a- prevents neutrophil recruitment

5. inhibit MAC formation- gram neg make proteins to stop this

how to bacteria evade phagocytes? (4)

1. target chemoattractants- S.aureus CHIPS stop neutrophil chemotaxis

2. inhibit complement by reducing recognition/opsonisation- S.aureus protein A inhibits C1q

3. alter surface structures- modify lipid A to reduce TLR4 sensing

4. capsular polysaccharide- blocks Ab and C3b binding such as S.PNEUMONIAE

how do bacteria interfere with phagocytosis machinery?

1. disrupt actin cytoskeleton via Rho GTPases- P aeruginosa Exot- polar condensation of actin and stops spinle

2. inject host mimicking proteins- Type III secretion

3. block Fc receptor signalling- no wasp, no gtpases- no pseudopod formation

how is phagocytosis signalling triggered? how do bacteria interfere?

• triggered: opsonised bacteria bind with Fc receptors and activates SRC kinases→ phosphorylates WASP- activates GTPases and F actin is remodelled to make pseudopods to engulf bacteria

• bacterial interfere: secrete TYPE III- mimics and disrupts GTPases and WASP- no remodelling

discuss staph. aureus defences and evading (5)

1. alteration of the surface charge: modifies LTA with D alanine and phospholipid with L lysine- reduce charge of bacteria so AMPs aren’t attracted to it

2. complement evasion- blocks C1q- protein A makes the antibodies bind in the wrong way. CSIN stops C3 convertase.

3. target chemoattractants- S.aureus CHIPS stop neutrophil chemotaxis

4. staphyloxanthin disrupts ROS

5. PVL toxin- neutrophil apoptosis at low conc