Adaptive Immunity

Question 0

What are the types of antigen-presenting cells?

Answer 0

Interdigitating dendritic cells - lymph nodes
Langheran’s cells - skin
Macrophages - various tissues
B cells - lymphoid tissues

Question 1

Give features of antigen presenting cells

Answer 1

Placed in strategic locations eg mucous membranes, lymphoid organs and all lymphoid tissue
Pathogen capture to present pathogen
Diversity in pathogen recognition receptors

Question 2

Which cells do antigen presenting cells present to?

Answer 2

T cells

Question 3

When dendritic cells sense an extracellular microbe, what do they do?

Answer 3

Phagocytose it
Migrate to regional lymph nodes
Process the antigen
Mature into cells capable of activating naïve T cells

Question 4

What is required to activate a naïve T cell?

Answer 4

Recognition of an antigen-MHC complex by the T cell’s TcR

Interaction of surface molecules on T cell antigen presenting cell

Question 5

What are the surface molecules on T cells and antigen presenting cells which interact?

Answer 5

APC: CD80, CD86

T cells: CD28

Question 6

Which cells are class 1 MHCs found and therefore which type of microbes do they present the antigens of?

Answer 6

All nucleated cells

Intracellular microbes eg viruses, bacteria, protozoa

Question 7

Which type of T cell do class I MHCs activate?

Answer 7

CD8+

Question 8

When an MHC class I activates a T cell, what happens?

Answer 8

CD8 is cytotoxic so kills the infected cell

Question 9

Which cells are class II MHCs found on and so which type of microbial antigens do they present?

Answer 9

Dendritic cells, macrophages and B cells

Extracellular microbes such as bacteria, parasites, fungi, worms

Question 10

What type of T cells do MHC class II activate?

Answer 10

CD4+ (T helper cells)

Question 11

Once activated, what do CD4 cells do?

Answer 11

Activate B cells, natural killer cells, macrophages and other phagocytes to enhance the immune response

Question 12

What do cytotoxic CD8 cells do?

Answer 12

Destroy infected cells with the same antigen as presented by the antigen presenting cells with MHC II

Question 13

What do naïve B helper cells do?

Answer 13

Have antibodies which can recognise antigens of pathogens

Can then engulf and process the pathogen and present it on MHC II to the activated T helper cell

Question 14

What happens when the naïve B cell has presented the antigen to the T helper cell?

Answer 14

The T helper cell activates the B cell so that is can differentiate into either a plasma cell or a memory cell

Question 15

What do plasma cells do?

Answer 15

Produce soluble antibodies against the pathogen that triggers effector mechanisms to eliminate pathogens

Question 16

What can memory cells do?

Answer 16

Have memory of the specific antigen and so can be removed quickly in the future

Question 17

What can antibodies do?

Answer 17

Recognise specific antigens, then

• neutralise pathogens (prevent bacterial adhesion to healthy cells)
• opsonise pathogens (promote phagocytosis by coating the antigen)
• activate complement (allows opsonisation and induce cell lysis of the pathogen

Question 18

What is the endogenous processing pathway of antigens?

Answer 18

Host cell digests cytoplasmic proteins of the intracellular pathogen by a specialised enzyme complex - cuts it into small peptides
Transporter associated with antigen processing (TAP) moves the peptide into the ER
Here it is coupled to an MHC I and transported to the cell surface

Question 19

Explain the exogenous processing pathway of antigens

Answer 19

After maturation in lymph nodes, lysosome-associtaed enzymes digest the pathogen to produce smaller peptides
Dendritic fell displays the antigenic peptides on its surface, completing them to MHC II molecules
Complex recognised by at cells passing through the lymph nodes and CD4+ cells activated

Question 20

What is a cytokine?

Answer 20

Any of various small regulatory proteins that regulate the cells of the immune system

Question 21

What are antibodies/immunoglobulins produced by?

Answer 21

B lymphocytes - they are membrane bound

Plasma cells - produce soluble ones

Question 22

What does the constant region of the antibody do?

Answer 22

Determines the type of antibody (IgE, IgA etc.)

Question 23

What gives the variable region uniqueness?

Answer 23

Different amino acid sequences

Question 24

What are the sites called within the antigen that the antibody recognises?

Answer 24

Epitopes

Question 25

Features of MHCs?

Answer 25

Co-dominant expression - both parental gene types are expressed to increase the number of MHC molecules

Polymorphic genes - different alleles among different individuals increased the presentation of different antigens/microbes

Question 26

Features of IgG?

Answer 26

Only antibody to be transferred across the placenta so protects baby for a short time after birth
The most abundant antibody
Can opsonise antigens for phagocytosis
Activates complement
Takes part in antigen-dependent cytotoxicity processes with NK cells and macrophages

Question 27

Features of IgA?

Answer 27

Distributed in serum, nasal discharge, saliva, breast milk, bowel fluid
Protects GI tract of newborns via mother’s breast milk
Mostly involved in mucosal defences
Prevents adhesion to gut wall and neutralises viruses

Question 28

Features of IgD?

Answer 28

Present on surface of B cells

Role in induction of antibody production

Question 29

Features of IgE?

Answer 29

Involved in immunity against parasites

Allergic reactions