Overview of immunology

Question 1

Define an antigen

Answer 1

Anything the immune
system responds to
Usually protein
Not necessarily ‘bad’

Question 2

Define an antigen receptor

Answer 2

Recognises the antigen
Fundamental basis of immunity
Basis of division into innate and adaptive

Question 3

Define effector mechanism

Answer 3

An action to respond to the antigen

Question 4

Whats the function of neutropril

Answer 4

Phagocytosis

Question 5

What’s the function of eosinophil

Answer 5

Infections

Question 6

What’s the function of monocyte (circulating macrophage tissue)

Answer 6

Phagocytosis, antigen presentation

Question 7

What’s the function of dendritic cells

Answer 7

Antigen presentation

Question 8

What’s the function of basophil (tissue-resident counterpart=mast cell)

Answer 8

Infections

Question 9

Describe B cells

Answer 9

B cells: make antibody, antigen presentation

Question 10

Describe T cells

Answer 10

T cells
CD4: help other components of immunity

CD8: kill infected cells

Question 11

Describe NK cells

Answer 11

NK cells: actually INNATE lymphocytes

Direct lysis of infected cells and antibody-dependent cellular cytotoxicity

Question 12

Describe cytokines

Answer 12

Cytokines are small proteins released by cells that have an effect on another cell

They are important for communication between cells of the immune system and between immune system cells and other cells and tissues

Question 13

Describe chemokines

Answer 13

Different structure, receptors and nomenclature from cytokines

Main role is temporal and spatial organisation of cells and tissues

Question 14

Describe antigen receptors

Answer 14

The receptor that cells use to recognise antigen is a key concept in immunology, and forms the basis of separating two immunological arms: innate and adaptive

Question 15

Describe the key features of innate antigen receptors

Answer 15

Do not recognise antigen specifically

Pattern recognition receptors’ (PRRs)

Recognise ‘pathogen associated molecular patterns’ (PAMPS)

Genome-encoded

Not clonally distributed

Question 16

Describe manose binding ligand (MBL)

Answer 16

MBL binds with high affinity to mannose and fucose residues with correct spacing

Mannose and fucose residues that have different spacing aren’t bound by MBL

Question 17

Discuss the Classical features of innate immune receptors/ defences

Answer 17

Work quickly – first line of defence

Adaptive immunity takes more time to be activated

Unable to ‘learn’, as germline encoded and therefore cannot change – therefore no memory

Question 18

Discuss the key features of adaptive antigen receptors

Answer 18

Recognise antigen specifically

T cell receptor, B cell receptor (antibody)

Produced by random somatic recombination events between gene segments

Huge receptor diversity

Clonally distributed

Permit specificity and memory in immunity

Question 19

Describe B cell receptors

Answer 19

B cell receptor (antibody) may be surface-bound or secreted

Recognises intact antigen

Question 20

Describe T cell receptors

Answer 20

T cell receptor is very similar to the B cell receptor

Only a surface receptor on CD4 and CD8 T cells

Recognises processed antigen in the form of linear peptides

Question 21

Describe the Generation of adaptive immune receptor by somatic recombination events

Answer 21

T and B cell receptors are produced by random recombination events between V, (D) and J gene segments, producing a huge receptor diversity despite a small number of genes.

The most useful receptors are selected after birth upon exposure to pathogens

Question 22

Describe the CD8 T cells process

Answer 22

Virus infects cell

Viral proteins synthesised in cytosol

Peptide fragments of viral proteins bound my MHC class 1 in ER

Bound peptides transported by MHC class 1 to the cell surface

CD8 T cells: peptide + MHC class I
Cytotoxic T cells kill virus-infected cell

Question 23

Describe the CD4 T cells process

Answer 23

Antigen is taken up into intracellular vesicles

In early endosomes of neutral pH endosomal proteases are inactive

Acidification of vesicles activates proteases to degrade antigen into peptide fragments

Vesicles containing peptides fuse with vesicles containing MHC class II molecules

Antigen-presenting cell

Question 24

Give some examples of effector mechanisms

Answer 24

Barriers (skin, acid pH in gut etc etc)
Cytokines
Complement
Phagocytosis (enhanced by opsonisation)
Cytotoxicity (CD8 T cell, NK cell)
Antibody-dependent cellular cytotoxicity
Mast cell and eosinophil degranulation

Question 25

What is adaptive immunity defined by?

Answer 25

Effector mechanisms are shared between innate and adaptive immunity. Adaptive immunity is defined by its receptors not by its effector mechanisms

Question 26

Describe acute inflammation

Answer 26

Cardinal features: hot, painful, red, swollen

Describes a process, but tells you nothing of the cause

Blood vessel changes underlie the process

Vasodilatation
Adhesion molecules
Increased permeability

The clinical features are therefore defined by an interaction between the pathogen and host immunity