Innate Immune Components

Question 1

What are the components of the innate immune systems?

Answer 1

barriers, soluble factors (complement, chemokines, cytokines) and cells (neutrophils, macrophages, NK cells)

Question 2

Why are epithelial cells important in innate immunity?

Answer 2

Because they provide both a physical barrier but also produce microbicidal and inhibitory molecules

Question 3

What are complement proteins?

Answer 3

Complement proteins are pro-enzymes in circulation that are part of the innate immune system

Question 4

What are the results of the complement protein cascade?

Answer 4

Inflammation, chemotaxis, opsonisation and lysis

Question 5

What are the three pathways in the cascade?

Answer 5

Classical, Alternate and Mannin binding lectin

Question 6

What is the common step in the three complement pathways?

Answer 6

Proteolysis of C3 to C3a and C3b

Question 7

What happens in the alternate pathway?

Answer 7

C3 is spontaneously hydrolysed into C3a and C3b

Question 8

What happens in the classical pathway?

Answer 8

C reactive proteins activate the C1 complex. The C1 complex binds to the Fc region of antibodies when they are bound to an antigen to activate the C1 complex. The activated C1 complex cleaves C4 into C4a and C4b and C2 into C2a and C2b. C4b and C2b are a C3 convertase which splits C3 into C3a and C3b

Question 9

What happens in the mannin binding lectin pathway?

Answer 9

The mannin binding lectin protein binds to mannose sugars on microbes. It acts in a similar way to the C1 complex to give proteolysis of C3 to C3a and C3b

Question 10

What happens in the final common steps of the complement pathway?

Answer 10

C3b recruits other proteins and forms a C5 convertase which splits C5 into C5a and C5b. C5b joins with C6, C7, C8. C8 recuits C9. This forms a membrane attack complex.

Question 11

How is inflammation a result of the complement cascade?

Answer 11

Via C3a and C5a

Question 12

How is chemotaxis a result of the complement cascade?

Answer 12

Via C5a

Question 13

How is opsonisation a result of the complement cascade?

Answer 13

Via C3b

Question 14

How is lysis a result of the complement cascade?

Answer 14

Via the membrane attack complex (MAC)

Question 15

What are the roles of macrophages?

Answer 15

phagocytosis, secretion of factors, release lysosymal contents (cytotoxic) and present antigens to T cells

Question 16

Where are the PRRs of macrophages and dendritic cells?

Answer 16

Some are extracellular, some are intracellular, depending on which kind of PAMPs they respond to

Question 17

What is the important adapter protein in TLR signalling?

Answer 17

My D88

Question 18

What is an inflammasome?

Answer 18

multi-molecular IL-1 activating machine

Question 19

What makes up the inflammasome?

Answer 19

NLRs and caspases

Question 20

What happens in phagocytosis?

Answer 20

First bind opsonised organism, then form phagosome (vacuole) to trap microbe, phagosome and lysosome fuse (phagolysosome), then digestion and release of microbial products

Question 21

What cells are phagocytic in innate immunity?

Answer 21

Neutrophils and macrophages

Question 22

What cells are cytotoxic in innate immunity?

Answer 22

NK cells, macrophages, eosinophils

Question 23

What cells are important in parasite immunity?

Answer 23

Eosinophils and basophils

Question 24

What cells are important in allergy?

Answer 24

eosinophils and basophils

Question 25

How do eosinophils attack parasites?

Answer 25

Eosinophils don’t have PRRs, can only bind to IgE via Fc receptors. IgE itself binds to the parasite.

Question 26

How do natural killer cells know which cells are infected by viruses?

Answer 26

Virus infected cells down regulate MHC class I to evade T cell killing. When NK cells bind to a normal cell, MHC class I acts as inhibition. If there is no MHC class I present - there is no inhibition so NK cell can bind and kill.