Initiation of Acquired Immune Responses - B cells

Question 1

What are the B cells the source of?

Answer 1

Soluble antibodies

Question 2

How are T and B cells trained to not self destroy?

Answer 2

Usually they are destroyed or inactivated when they try to react with self-antigens

Question 3

What is an antigen?

Answer 3

Any substance which can cause an adaptive immunity activating B and T cells

Question 4

What is an antibody?

Answer 4

A protein that is produced in response to a particular antigen

Question 5

What is between the heavy chain and the light chain of antibodies?

Answer 5

The variable antigen binding site

Question 6

How many polypeptide chains do antibodies have?

Answer 6

4 - 2x light and 2x heavy

Question 7

What do B cells use as receptors?

Answer 7

Membrane-bound antibodies to recognise and bind to antigens (IgM or IdD)

Question 8

What are the 5 classes of antibodies?

Answer 8

IgM, IgG, IgA, IgE and IgD

Question 9

Where do antigen specific T and B cells develop?

Answer 9

Primary lymphoid tissues - bone marrow (B cell), thymus (T cell) and spleen

Question 10

What is the process of Transendothelial Migration?

Answer 10

Lymph flows into lymph nodes through afferent lymphatic vessels.
B and T cells enter lymph nodes through High Endothelial Venules (HEV).
B cells come through HEV straight into the lymphoid follicle
T cells come through HEV and stay in the T-cell area of the lymph node and interact with dendritic cells that come in through the afferent lymph

Question 11

How do lymph and lymphocytes leave the lymph node?

Answer 11

Through the medullary sinus and then efferent lymphatic vessels. efferent lymph eventually get back into blood circulation via the subclavian vein

Question 12

What happens when B cells are activated?

Answer 12

B cells clonal proliferate and differentiate in 2 types of effector cells - Plasma or Memory B cells

Question 13

What are plasma cells (B)?

Answer 13

Produce and secrete soluble, antigen-specific antibodies

Question 14

What are memory B cells?

Answer 14

Long lived cells that continue to circulate around the body

Question 15

How do B cells encounter antigens?

Answer 15

Specialised cells within B cell zones can ‘trap’ opsonised antigen which express opsonin receptors

Question 16

What happens once a B cell has encountered an antigen?

Answer 16

To become fully activated, B cells need to receive 2 signals to become fully activated and clonal proliferate - antigen and ‘helping’ cells

Question 17

What do the proliferate cells from B cells form?

Answer 17

A secondary folic - the Germinal Centre (tends to be where cancers arise)

Question 18

What happens when the B cells have proliferated sufficiently?

Answer 18

Stop proliferating and differentiate into antibody-secreting plasma cells, which recognise the same specific antigen as the original parent B cell

Question 19

What are the first type of antibody secreted by plasma cells?

Answer 19

Low affinity (antigen-specific) IgM antibodies

Question 20

What do T helper cells do?

Answer 20

Help production and secretion of ‘better’ antibodies from B cells that are reacting to protein antigens

Question 21

How do T helper cells help produce better antibodies?

Answer 21

Switch from low to high affinity antibody production
Switch from producing IgM to IgG antibodies (or IgA or IgE) - IgG can act as an opsonin
B cells can differentiate into LONG-lived plasma cells
Stimulate production of antigen-specific memory B cells

Question 22

What are the differences in antibody classes?

Answer 22

Different heavy chains (same basic structure and same antigen-specificity)

Question 23

Why are long-lived plasma cells important?

Answer 23

Go from lymph node to bone marrow and remain secreting antibodies for years

Question 24

How do antibodies help kill and eliminate pathogens?

Answer 24

Recognition function and effector function

Question 25

What is recognition function?

Answer 25

Binding to antigen, mediated by variable region site

Question 26

What is effector function?

Answer 26

Clearance mechanisms mediated interaction of the heavy chain constant region with effector molecules (complement and Fc receptors, Fc = fragmented crystal)

Question 27

What does membrane bound IgM do?

Answer 27

Serves as the B cell antigen receptor

Question 28

What is agglutination?

Answer 28

Clumping of particles caused by antibody molecules binding to antigens on the surface of two adjacent particles

Question 29

What antibody classes mediated agglutination?

Answer 29

IgM and IgG

Question 30

What does agglutination do?

Answer 30

Increases the efficacy of pathogen elimination by enhancing phagocytosis. Can also prevent viruses from binding to and infecting host cells

Question 31

What activates the classical complement pathway?

Answer 31

The Fc region of IgM (only one required as it can bind many antigens at once) and IgG (several different ones must bind closely located antigens to recruit and activate C1) antibodies

Question 32

What are the functions of IgG?

Answer 32

Agglutination, complement system activation, foetal immune protection, neutralisation, opsonisation and NK activation

Question 33

What happens to IgG in the foetus?

Answer 33

Transported across the placenta into foetal blood circulation

Question 34

How does IgG help on neutralisation?

Answer 34

Prevents viruses from infecting host cells and prevents microbial toxins from disrupting normal cell function though the binding of high affinity neutralising antibodies

Question 35

Why are IgG good opsonins?

Answer 35

As phagocytes express a type of Fc receptor that binds specifically to the heavy chain of IgG

Question 36

How are natural killer cells activated?

Answer 36

Innate immune reposone or adaptive immune response by IgG

Question 37

What do membrane bound IgD do?

Answer 37

Serves as the B cell antigen receptor to activate B cell

Question 38

Where is the monomeric form of IgA found?

Answer 38

In blood serum

Question 39

What does the dimeric form of IgA do?

Answer 39

Neonatal defence and neutralisation at mucosal sites (present in secretory fluids)

Question 40

Where are secreted IgA antibodies transported to?

Answer 40

Colostrum and breast milk in order to protect the GI tract of neonates

Question 41

What does IgE do?

Answer 41

Trigger allergic response eg asthma and anaphylaxis

Question 42

How many Fc sites must each C1 bind to for a stable interaction?

Answer 42

At least 2 - results in a conformational change in Fc exposing a binding site for complement proteins that ends in the production of a C3 cleaving enzyme