Adaptive Immunity

Question 1

What is adaptive immunity?

Answer 1

Immunity that is induced by the presence of foreign material
Specific

Question 2

Examples of adaptive immunity:

Answer 2

B cells
T cells

Question 3

Where do B and T cells develop?

Answer 3

B cells: Bone marrow
T cells: Thymus

Question 4

Where do B and T cells circulate in their inactive form?

Answer 4

Around their primary lymphoid tissue (site of development)

Question 5

How are B and T cells activated?

Answer 5

By antigens in the secondary lymphoid tissue
E.g. lymph nodes

Question 6

What happens when B cell encounters antigens (4)?

Answer 6

1. Membrane-bound antibodies on the B cells bind to target antigen IgM within the B cell zone of lymph nodes
2. Activated by antigen signals and ‘helper signals’
3. B-cells clonally proliferate and become antibodies or a memory B cell
4. IgM (high affinity) and IgG (produced by B cells responding to certain antigens) antibodies produced

Question 7

Dendritic cells function

Answer 7

Act as a bridge between the innate and acquired immune system
Express antigens on their cell surface and present them to T cells

Question 8

What is the complement system and how is it activated?

Answer 8

Activated in response to inflammation and creates a cascade of chemical reactions

Question 9

MBL pathway (5):

Answer 9

1. C3 is cleaved into the active C3a and C3b
2. C3b can then cleave C5 into C5a and C5b
3. C3b can then amplify the reaction via the alternative pathway, causing more C3 to cleave into C3a and C3b
4. C5b produces the membrane attack complex, which inserts into cell walls and destroys the cell by letting salt and water in
5. C3a and C5a are responsible for acute inflammation

Question 10

What are acute phase proteins?

Answer 10

Proteins produced by the liver whose plasma concentrations increase or decrease in response to inflammation

Question 11

Role of CRP

Answer 11

Activates complement via classical pathway
Rapidly increases during inflammation
Short half life - decreases rapidly after

Question 12

Role of MBL:

Answer 12

Activates complement via MBL pathway

Question 13

Role of CD4 + T cells

Answer 13

activate B cells & stimulate production of memory B cells

Question 14

Role of CD8 + Killer T cells

Answer 14

Kill infected cells via perforin/granzymes/granulysin

Question 15

Antibody structure:

Answer 15

Made up of 2 light chains and 2 heavy chains

Each has a unique variable region (antigen binding site) which is specific against one antigen

Question 16

Where are membrane bound antibodies located?

Answer 16

On the surface of B cells

Question 17

T-cell antigen receptor (TCR):

Answer 17

Can only recognise peptide antigens that are presented by MHC molecules

Question 18

Class I MHC

Answer 18

Expressed on all nucleated cells
Present peptide antigens to CD8+ killer T cells

Question 19

Class II MHC:

Answer 19

Expressed only on antigen presenting cells (e.g. dendrites, macrophages)
Present peptide antigens to CD4+ helper T cells

Question 20

How do T cells encounter antigens (5)?

Answer 20

1. Dendritic cells recognise and phagocytose antigenic debris
2. In the presence of pro-inflammatory mediators, the dendritic cells mature and increase expression of stimulatory molecules on their surface
3. Dendritic cells phagocytose the pathogenic antigens, break the antigens down into short peptides and load them onto MHC II molecules
4. MHC II molecules transported to cell surface
5. Co-stimulatory molecules enable T cell to respond to antigen and fully differentiate

Question 21

Examples of ‘helper signals’

Answer 21

TH cells
PRR and PAMPS
Multiple antigens

Question 22

Secreted antibodies:

Answer 22

Secreted by plasma cells
Present in serum and tissue fluid

Question 23

IgM antibodies:

Answer 23

First antibody to be made in an inflection
Monomer when bound to B cell membrane but pentamer when released into plasma

Question 24

IgM antibodies function:

Answer 24

B cell activation
Agglutination
Complement system activation through classical pathway

Question 25

Aggluation:

Answer 25

When antibody cross-links multiple antigens producing clumps of antigens Prevents viruses from binding to host cells Enhances phagocytosis

Question 26

IgG antibodies:

Answer 26

Most abundant antibody in plasma Monomer Dominant type during secondary response

Question 27

IgG antibody function:

Answer 27

Foetal immunity Complement activation NK cell activation Neutralisation

Question 28

IgD antibodies and their function:

Answer 28

Second least abundant antibody Monomers B cell activation

Question 29

IgA antibodies:

Answer 29

Second most abundant antibody Monomer in serum

Question 30

IgA functions:

Answer 30

Helps with neutralisation of pathogens Dimmer in secretory fluids (e.g. colostrum in great milk) Neonatal defence - protects GI tract of neonates

Question 31

IgE antibody and function:

Answer 31

Least abundant Monomer Produced in allergic reactions

Question 32

What two signals do B-cells require to become fully active?

Answer 32

Antigen signals Helper signals

Question 33

Germaline centre response

Answer 33

Production of memory B-cells

Question 34

What do CD4 + T cells differentiate into?

Answer 34

T helper cells

Question 35

What do T helper cells differentiate into?

Answer 35

Effector TH cells

Question 36

Examples of effector TH cells:

Answer 36

TH1 TH2 TFH

Question 37

Function of TH1 cells:

Answer 37

Migrates out of lymph nodes and travels to infected area Secrete pro-inflammatory cytokines which stimulates production of ROS (macrophage-mediated)

Question 38

What do CD8 + T cells differentiate into?

Answer 38

CTLs (Cytotoxic T Lymphocytes)

Question 39

Role of IL-2

Answer 39

Provided from TH cells Promotes differentiation and proliferation of antigen activated CD8+ cells into CTLs

Question 40

How are antigens activated on CD8+ cells?

Answer 40

By MCH I

Question 41

Role of CTLs (3):

Answer 41

Migrate out of secondary nodes to site of infection via transendothelial migration Kill virally infected host cells by recognising pathogenic antigens attached to MHC class 1 Involved in killing cancer cells

Question 42

Role of TH2 cells:

Answer 42

Secrete IL4, IL5 and IL6 which: - Promote B cell proliferation - Induces antibody production

Question 43

Role of TFH cells:

Answer 43

Stimulated by presented antigen peptides + MHC II molecules on B cell Stimulate the B cells to proliferate and differentiate (plasma + memory) by secreting IL4 and IL21