2. Innate Immunity

Question 1

What are collectins and how can they activate complement?

Answer 1

Pattern Recognition Receptors

• Lectin head binds to sugars on bacterial surfaces
• Collagen tail binds to phagocytes

activates complement cascade

Host cells are protected via sialic acid covering mannose

E.g MBL

Question 2

Ficolins

Answer 2

Trimer molecule that recognises acylated compounds on bacterial cell walls

• opsonisation
• activate complement

Question 3

What is complement

Answer 3

proteins floating around that cause a series of reactions before immune cells take action

Part of innate immunity

Question 4

Heriditary Angioedema

Answer 4

C1 inhibitor deficiency

-no inhibition so C1 can’t inhibit C4 and C2

Question 5

Describe the classical pathway of the complement system

Answer 5

Binding of C1 to Ag-Ab complexes activates classical pathway

C2 and C4 is cleaved off

C3 convertase (C4b2a)

Question 6

Describe the alternative pathway of the complement system

Answer 6

• Activated by C3b or C3i binding to microbial surfaces
• C3 spontaneously splits into C3a and C3b
• C3b binds to a cell membrane and factor B, making it susceptible to cleavage by factor D to Bb
• C3bBb (aka C3 convertase) can hydrolyse more C3 creating more C3b which can amplify the signal
• C2bBb and C3b=C3bBbC3b aka C5 convertase

….MAC

Question 7

Describe the lectin pathway of the complement system

Answer 7

• Antibody independent
• Activated by ficolins with MBL- these bind carbohydrates
• Forms complex with MASP-1 and MASP-2 after binding with MBL
• Active complex cleaves C2 and C4

Question 8

Lysozyme

Answer 8

Antimicrobial enzyme

• Found in tears, saliva
• Disrupts bacterial cell wall

Most effective against Gram-positive bacteria

Question 9

Antimicrobial peptides

Answer 9

Amino acid chains secreted by neutrophils, paneth cells (SI)
-cover epithelial surfaces, found in saliva

• Disrupts bacterial membrane
• Attacks fungi and viruses
• Inhibits RNA and DNA synthesis

Question 10

Collectins, ficolins and pentraxins
What are they?
Actions?

Answer 10

Soluble innate immune molecules

-Act as opsonins
bind to pathogens targeting them for phagocytosis

activate complement through the classical/lectin pathway

Question 11

Activated by C3b or C3i binding to microbial surfaces . This best describes which complement pathway?

Answer 11

Alternative pathway

Question 12

MASP1 and MASP2 assembling on MBL best describes which complement pathway?

Answer 12

Lectin pathway

Question 13

Complement System Pathways and initiators

Answer 13

• Classical: C1q
• Alternative: C3b (“tick over”)
• Lectin: MBL/Ficolins

Question 14

2 consequences of complement deficiencies

Answer 14

• Heriditary Angioedema
• Recurrent infections
• pts deficient in C8 suceptible to infections with N.meningitis

Question 15

What can deficiency in C4 lead to?

Answer 15

90% develop SLE

C4 deficiency means less C3b (C4b2a is C3 convertase)

Question 16

MAC

Answer 16

MAC forms a pore that inserts into the membrane allowing diffusion of ions and small molecules
water moves into cell killing it