Immunology- Introduction to B cells and antibodies

Question 1

What are the specific antibodies involved in humoral immunity?

Answer 1

IgD 
IgM  
IgG  
IgA  
IgE

Question 2

What does IgD do?

Answer 2

Antigen receptor virgin B-cells

Question 3

What does IgM do?

Answer 3

Agglutinin; activates complement

Question 4

What does IgG do?

Answer 4

Opsonin; activates complement

Question 5

What does IgA do?

Answer 5

Secretory; protects mucosa

Question 6

What does IgE do?

Answer 6

Inflammatory; protection vs helminths

Question 7

Define the non-specific movements in humoral immunity?

Answer 7

Complements
Cytolysis 
Chemotaxis
Inflammation
Opsonisation

Question 8

How do B cells respond to antigens?

Answer 8

The stay within the lymphatic tissue and respond to antigens by differentiating into plasma cells.

Question 9

Explain the activation of B cells?

Answer 9

B cells are activated by B cell receptors which bind to specific antigens
B cells in lymphatic tissues respond to either unprocessed antigens or antigens presented on a APC.

Question 10

How do B cells respond to a foreign antigen?

Answer 10

They initially respond to foreign antigens by taking in some of the antigens molecules and combining the antigen fragments to an MHC 2.
This complex is then recognised by helper t-cells allowing the realise of cytokines such as IL-2 IL-4 and IL-6.
These co stimulate B cells and activates them allowing differentiation into plasma cells which secrets antibodies to a specific antigen. Some do not differentiate into a plasma cells they will sometimes differentiate into a memory cells.

Question 11

What components are antibodies made up of?

Answer 11

2 identical heavy chain made up f 450 amino acids
2 identical light chains made up of 220 amino acids.
The 2 light chain are bonded to the heavy chains via disulphide bridges.
The 2 heavy chains are also joined together via disulphide bonds which forms a hinge.

Question 12

What are the 2 antibody regions?

Answer 12

Constant region

Variable region

Question 13

What is significant about the variable region of an antibody?

Answer 13

It is specific on every antibody as it needs to be complimentary to the antigen.

Question 14

How many isotopes does the antibody have?

Answer 14

5

Question 15

Name the 5 antibody isotopes?

Answer 15

IgG
IgE
IgA
IgM
IgD

Question 16

What are the 3 ways antibodies target antigens via antibody-antigen binding?

Answer 16

Agglutination- where antibodies form cross linkages to form clumps.
Neutralisation- antibody covers the biologically active form of a microbe or toxin.
Precipitation- Forms cross linkages forming insoluble antigen antibody complex

Question 17

Name the 3 ways the Fc portion of the antibody bind to target cells?

Answer 17

Complement fixation- Fc region binds to complement protein and complement system becomes activated.
Opsonisation- Fc region binds to receptors on the phagocytic cells activating phagocytosis.
Activation of NK cells- Fc region binds to NK cells triggering release of cytotoxins.

Question 18

What are the complement proteins

Answer 18

C1-C9

Question 19

What are the complement factors?

Answer 19

Factor B; Factor D; Properdin

Question 20

What are the complement receptors?

Answer 20

Complement receptors [CR] CR1; CR2; CR3

Question 21

What are the 3 complement pathways?

Answer 21

1. Alternative Pathway (innate)
2. Classical pathways
3. Lectin pathways

Question 22

Explain the mechanism of the classical complement pathway?

Answer 22

1. Antibody [IgM or IgG] binds to epitopes of antigen
2. C1 binds to Fc region of antibodies
3. C1r activates C1s which is a proteinase
4. C1s cleaves C4
5. C4b binds to antigen; C4a remains in fluid phase
6. C1s cleaves C2
7. C2b binds to antigen; C2a remains in fluid phase
8. C2b is a proteinase which cleaves C3
9. C3b binds to antigen; C3a remains in fluid phase
10. C2b cleaves C5
11. C5b does not spontaneously bind; C5a in fluid phase
12. C5b does not spontaneously bind; C5a in fluid phase
13. C5b678 binds to the lipid bi-layer
14. C9 [pore forming protein] inserts hole into the membrane
15. Microorganism is lysed by the membrane attack complex

Question 23

What is the function of the membrane attack complex?

Answer 23

Forms pores in lipid bi-layer membranes of microorganisms

Question 24

Which bacteria does MAC destroy and which one does it not?

Answer 24

Kills Gram-negative bacteria, enveloped viruses and some protozoan parasites
Gram positive bacteria protect themselves from complement mediated lysis by their thick peptidoglycan cell walls
Fungi protect themselves from complement mediated lysis by their thick chitin cell walls

Question 25

what is the function of C3a and C5a?

Answer 25

Although gram +ve bacteria can not be killed it can try to eliminate it from the body. C3a and C5a are “anaphylatoxins” they activate mast cellsC3a and C5a are chemotaxins. They attract phagocytes (neutrophils and mononuclear pahgocytes)C3b is an opsonin; it enables phagocytes to recognise and bind to antigens and phagocytose them

Question 26

How does the alternative pathway work?

Answer 26

Doesn’t involve antibodies - innate immunityInteractions between microbial surface polysaccharides and factors B, D and P. this interaction then activates complement protein C3, which in turn activates the enzyme cascade

Question 27

What occurs if the same antigen infects the body again. How does the immune system respond?

Answer 27

After contact with a new antigen there is a steadily increases in the antibody titer, first IgM, then IgG, this antibody titre then steadily decreases. The initial contact with an antigen is called the primary response. If the antigen is encountered a second time the memory cells become activated – the secondary response.In the secondary response, the memory cells quickly proliferate and produce vast quantities of mostly IgG antibodies. Immunological memory provides the basis if vaccination.

Question 28

Does the immune response remain the same in an ageing individual. If not why?

Answer 28

As individuals age they tend to become more susceptible to infectious diseases. This is mostly associated with lower levels of immune function. For example T cells become less responsive to antigens, and fewer T cells respond to infections. This may arise because of age related atrophy of the thymus, or decreased production of thymic hormones. Associated with the decrease in the numbers of t cells is a decrease in the number of b cells , so the antibody titre does not increase as rapidly in older individuals. Thus vaccinations against influenza are provided every year for older individuals.