Adaptive Immunity II

Question 1

What are B cells

Answer 1

• communicate with T cells
• have a specific B cell receptor for antigens
• B cells produce antibodies
• clonal expansion leads to generation of two subsets
• plasma cells are great big antibody factories
• memory B cells are important

Question 2

Where do B cells mature

Answer 2

Mature in bone marrow

Question 3

Describe B cell circulation

Answer 3

Circulate in the blood and the lymph they are found in large numbers in the lymphoid organs

Question 4

How do B cells recognise antigens

Answer 4

They recognise antigens through the B cell receptor (BCR) which is the actual antibody (lgM or lgD)

Question 5

When B cells are activated what do they change into

Answer 5

Plasma cells - antibody factories

Question 6

What are the three main receptors in adaptive immunity

Answer 6

• T cell receptor
• B cell receptor
• Major histocompatibility complex (MHC proteins)

Multiple genes encoding each allows the development of a repertoire of receptors with wide specificity

Question 7

What are the 5 types of immunoglobulins produced by B cells

Answer 7

LgG, lgE, lgD, lgM, lgA

Question 8

Describe the B cell receptor structure

Answer 8

Slightly different from T cell receptors, both have variable and constant regions, they have light and heavy chains

Question 9

Describe LgG antibodies

Answer 9

Account for 80% of all antibodies, they are responsible for resistance against many viruses, bacteria and bacterial toxins

Question 10

Describe lgE

Answer 10

Attaches as an individual molecule to the exposed surfaces of basophils and mast cells

Question 11

Describe lgD

Answer 11

Individual molecule on the surfaces of B cells, where it can bind antigens in the extracellular fluid, this binding can play a role in the sensitisation of the B cell involved

Question 12

Describe lgM antibodies

Answer 12

The first class of antibody secreted after an antigen is encountered. LgM concentration declined as LgG production accelerates, the anti-A and anti-B antibodies responsible for the agglutination of incompatible blood types are lgM antibodies

Question 13

Describe lgA antibodies

Answer 13

Found primarily in grandular secretions such as mucus, tears, saliva and semen. These antibodies attack pathogens before they gain access to internal tissues

Question 14

What is each development stage for B cells defined by

Answer 14

Defined by rearrangements of the immunoglobulin heavy and light chain genes

Question 15

Once in periphery B cells migrate to…

Answer 15

Secondary lymphoid organs

Question 16

Heavy B cell chains involves rearrangement of ….

Answer 16

Variable (V), Diversity (D) and Joining (J) genes

Question 17

Light chain involves rearrangement of….

Answer 17

Variable (V) and Joining (J) genes

Question 18

What is the B cell receptor

Answer 18

lgD

Question 19

Immature B cell receptor is mainly…

Answer 19

LgM

Question 20

Mature B cells express both….

Answer 20

LgM and lgD

Question 21

Describe negative selection of B cells

Answer 21

Undergo negative selection in the bone marrow, macrophages will engulf and remove self reacting B cells

Question 22

What are the three functions for antibodies in the human body

Answer 22

• Neutralisation
• Opsonization
• Initiation of complement

Primary goal is to prevent microbial activity and aid removal of threat from host

Question 23

Describe opsonisation

Answer 23

Refers to coating of pathogens by antibodies or complement proteins
- phagocytosis
- antibody dependent cellular cytotoxicity (ADCC)
- mast cell degranulation

Question 24

Describe complement initiation

Answer 24

Classical pathway - antibody attached to microbe

Question 25

Describe B cell activation

Answer 25

- antigens require T cell help are called thymus-independent antigens - occurs in lymph nodes - activation of naive B cells results in the rise of plasma cells - plasma cells are antibody factories

Question 26

Describe B cell activation (T cell dependent)

Answer 26

T cell and BCR interactions requires co receptor binding (CD40 to CD40L) - cytokine signals are released from T helper cell induce proliferation - generates a pool of plasma cells which produce antibody - also generates memory B cells - plasma cells initially produce IgM before undergoing class switching

Question 27

What is the first antigen produced after B cell activation and how many binging sites does it have

Answer 27

IgM and 10 binding sites

Question 28

Why does class switching take place

Answer 28

Activation leads to class switching due to lgM response being weak therefore they class switch to IgG (or IgA/IgE) This increases affinity for the antibody

Question 29

What does avidity mean

Answer 29

Ability of antibodies to form complexes Gives a measure of the overall strength of an antigen-antibody complex

Question 30

In lymphoid organs cross talk between B and T cells leads to

Answer 30

- humoral immunity - cellular immunity

Question 31

What are germinal centres

Answer 31

Hubs for T cells and B cells to cross talk and - proliferate and differentiate - somatic hypermutation (class switching)

Question 32

Describe vaccinations

Answer 32

B cells and T cells play a role in the process of vaccinations against a weak antigen, this leads to immunological memory, in the primary immune response IgM acts early but as B cells undergo class switching an IgG response follows Presence of memory T and B cells means that upon second exposure the immune system can respond much faster

Question 33

What is immunological tolerance

Answer 33

Sometimes the immune system can become dysfunctional and in a state of immune unresponsiveness to a particular antigen or set of antigens, two types central and peripheral

Question 34

Describe Central tolerance

Answer 34

Can cause autoimmune disease something goes wrong in the selection of B and T cells

Question 35

Describe peripheral tolerance of T cells

Answer 35

Not all self reactive T cells are eliminated however peripheral tolerance prevents their activation Signal 1 but no signal 2 results in anergy Signals 1 and 2 but no 3 (cytokine survival signal) results in deletion by apoptosis T regulatory cells can also directly block activity by binding antigen (both self and foreign antigens)

Question 36

Describe peripheral tolerance of B cells

Answer 36

- occurs in secondary lymphoid organs - self reactive B cells still require help from self reactive T cells - since most self reactive B cells do not receive any T cell help and therefore become anergic

Question 37

Describe the term breach of tolerance

Answer 37

Breach of tolerance to self antigens or commensal organisms drives many autoimmune diseases