WEEK 1 - bacteria and the immune system

Question 1

phagocytosis

Answer 1

uptake and destruction of bacteria

Question 2

antibody

Answer 2

oponization
- The binding to the surface of the bacterium of antibodies and other molecules that mark the organism for engulfing my phagocyte

Question 3

complement

Answer 3

lysis of bacteria
opsonization

Question 4

pathogen recognition by phagocytes

Answer 4

phagocytes have pattern recognition receptors (PRR)
- also called Toll-like receptors (TLRs)

these recognise a pathogen-associated molecular pattern (PAMP)
- peptidoglycan (in bacterial cell walls)
- LPS (outer membrane of gram -ves)
- flagellin (major subunit of flagella)
-(also recognises viral structures)

Question 5

action of macrophages

Answer 5

macrophage digest bacteria by phagocytosis
- primary lysosome fuses with phagosome
- phagolysosome becomes acidic and contains proteolytic enzymes

Question 6

antibodies

Answer 6

binds to specific antigens on the surface of bacteria
- pahocytosis is enhanced by opsinisation
- block adhesins
- initates complement cascade

Question 7

classical complement activation

Answer 7

1. antibodies bind to bacterial surface antigen
2. C1 binds to the Fc region of the antibodies
3. initates a cascade
   - cleavage and binding of serum proteins
   - C5b binds to an adjacent site on bacterial membrane
4. membrane attack complex forms pores in the bacterial membrane

Question 8

alternate complement pathways

Answer 8

complement can also be activated by:
- mannan binding lectin
–> serum protein
–> recognises polysaccharies found in bacterial walls
–> resembles C1 of classical pathway

• alternative pathway
  –> uses some components of the classical pathways
  –> other proteins required

Question 9

outcomes of complement activation

Answer 9

all complement pathways produce a C3 convertase
- cleave C3 to produce its active products C3a and C3b
–> which then lead down different pathways causing different outcomes

outcomes
- opsinisation (gram +ve and -ve bacteria)
- membrane attack complex formation (only gram -ve)
- inflammatory response –> mast cells release histamine

the antibody independent pathways are very important in neonates