Immunology Lecture 10

Question 1

Define complement.

Answer 1

Heat labile component of blood plasma.

Question 2

What are the three major functions of complement?

Answer 2

Defence against bacterial infection
Augmentation of the antibody response
Waste disposal

Question 3

Do complements require antibodies to act? Are they specific?

Answer 3

No antibodies required, are non-specific.

Question 4

What kind of reaction is the complement activation?

Answer 4

Sequential cascade.

Question 5

Name the three pathways of complement activation, and their activation requirement.

Answer 5

Classical - requires antibodies
Alternative - requires endotoxins/polysaccharides
Lectin - requires mannose-binding protein

Question 6

What are mannose-binding proteins released by?

Answer 6

Macrophages after phagocytosis.

Question 7

Describe the classical complement activation sequence in detail.

Answer 7

Antibody unforked end binds to the C1 complex, activating it.
C1 complex splits C2 into C2a and C2b, and C4 into C4a and C4b.
One C2a/b and one C4a/b fragment merge to form the enzyme C3 convertase.
C3 convertase hydrolyses C3 into C3a and C3b.
C3b converts C5 into C5a and C5b.
C5b, with one C6-8 and many C9s, forms a MAC - membrane attack complex, punching a hole in the membrane.

Question 8

Which complements form the MAC?

Answer 8

C5b, C6, C7, C8, and many C9s.

Question 9

What is required for C3 hydrolysis? What differs between the classical and alternative complement activation pathways?

Answer 9

A C2 and C4 fragment merging to form C3 convertase.

However, it can be hydrolysed without this enzyme. That is the alternative pathway.

Question 10

What is the controlling factor of complement activation?

Answer 10

C3 cleavage by C3 convertase, rate is slow unless infection present.

Question 11

What is the function of C3a and C5a?

Answer 11

Cause mast cells to release histamines, inducing inflammation.
C5a also attracts phagocytes.

Question 12

Define opsonisation.

Answer 12

When C3b coats a pathogen, enhancing phagocytosis.

Question 13

Name 4 phagocytic cells.

Answer 13

Monocytes
Macrophages
Neutrophils
Dendritic cells

Question 14

Define toll-like receptors, where they are found, and what they recognise.

Answer 14

Found on phagocytic cells. Recognise pathogens using TLRs, which recognise PAMPs on the pathogen surface - pathogen associated molecular patterns.

Question 15

Can a TLR recognise many PAMPs?

Answer 15

No, each has a limited range.

Question 16

Do self cells have PAMPs?

Answer 16

No.

Question 17

What happens when TLRs are activated?

Answer 17

Induces genes such as cyotkines, chemokines, and phagocytic genes.

Question 18

How does the innate immune system differentiate self from non-self?

Answer 18

Using TLRs.

Question 19

What happens after a pathogen is phagocytosed?

Answer 19

The bacteria is internalised as a phagosome.
Fuses with a lysosome forming a phagolysosome, and digested.
Phagolysosome is merged with cell membrane to discharge indigested material.

Question 20

What are cytokines?

Answer 20

Major control proteins for both specific and non-specific immune responses.

Question 21

Do cytokines have unique functions?

Answer 21

No, their functions can overlap.

Question 22

What relationship do cytokines have with stem cells?

Answer 22

Are involved in differentiation of stem cells to immune cells.

Question 23

Are cytokines autocrine, paracrine, or endrocrines?

Answer 23

All three.

Question 24

Are cytokines required in high concentrations to have an effect?

Answer 24

No, they are very effective at low concentrations.

Question 25

How do cytokines act?

Answer 25

Bind to specific cellular receptors to induce genes, such as fever.

Question 26

What is a natural killer cell?

Answer 26

Large, non-phagocytic granular cell.

Question 27

What do NK cells act on?

Answer 27

Malignant and infected cells.

Question 28

How do NK cells appear under a microscope?

Answer 28

Exactly like a lymphocyte.

Question 29

How do NK cells act?

Answer 29

They recognise antibosies on the cell surface, and also recognise the lack of MHC class 1.

Question 30

How can NK cells kill cancer cells?

Answer 30

They lack MHC class 1 markers, which NK cells can recognise the lack of.