Immunology 4- Acquired immune response and antibodies

Question 1

What two signals do B cells need to become fully activated and clonal proliferate?

Answer 1

• The antigen

- ‘helping’ signals

Question 2

What do activated B cells differentiate into?

Answer 2

Plasma cells.

Question 3

What are plasma cells?

Answer 3

Antibody secreting cells which are much larger than B cells and have many RER, meaning they can produce many antibodies.

Question 4

In what ways can B cells mutate and produce better antibodies?

Answer 4

Switch from low to high affinity antibody production.

Switch the class of antibody they produce (e.g. IgM> IgG).

Differentiate into long-lived plasma cells and long-lived memory B cells.

Question 5

Are IgM antibodies high or low affinity molecules?

Answer 5

Low affinity.

Question 6

Which type of antibody do plasma cells first produce?

Answer 6

IgM antibodies.

Question 7

What are the two signals needed from non-protein antigens for B cell activation?

Answer 7

1- BCR + antigen

2- PRR + PAMP

Question 8

why do B cells not need a second signal for antigens with multiple antigenic epitopes?

Answer 8

There is enough interaction to activate the B cell without a secondary signal.

Question 9

What do non-protein antigens and antigens with repetitive antigenic epitopes lead to?

Answer 9

• low affinity antibodies
• short lived plasma cells
• no memory cells

Question 10

What are the two signals needed from protein antigens for B cell activation?

Answer 10

1- BCR binding to antigen

2- Help from Th cells

Question 11

Through what process do B cells internalise protein antigens?

Answer 11

Endocytosis

Question 12

What do B cells do to receive help from Tfh cells?

Answer 12

The peptides derived from chopping up protein antigens are presented on the B cell surface as an MHC-II peptide signal. The Tfh cell can then bind to this signal. Tfh helps by secreting co-stimulatory molecules to help the B cell.

Question 13

How do Tfh cells help B cells?

Answer 13

They release co-stimulatory molecules. (help B cells produce antibodies)

Question 14

What is the germinal centre reaction?

Answer 14

Rapid proliferation

Question 15

What are the two parts of an antibody?

Answer 15

• The ‘recognition function’ at the top, mediates binding to antigen by variable region sites
• The ‘effector function’ at bottom, mediates clearance mechanisms by interaction of its heavy chain constant region and the effector molecules (complement or Fc receptors)

Question 16

Describe IgM.

Answer 16

• In its membrane-bound monomeric form, IgM serves as the B cell antigen receptor (mediates B cell activation)
• In its secreted (from plasma cells) pentameric form, IgM is the first Ig type produced during a humoral immune response, it is present in plasma and secretory fluids, its involved in agglutination and complement system activation

Question 17

What is agglutination?

Answer 17

The action of an antibody when it cross-links multiple antigens producing clumps of antigens.

Agglutination increases the efficacy of pathogen elimination by enhancing phagocytosis. It prevents viruses from binding and infecting host cells

Question 18

What two antibodies mediate agglutination?

Answer 18

IgM and IgG.

Question 19

Which pathway in the complement system is activated by the Fc region on IgM and IgG?

Answer 19

the classical pathway

Question 20

Describe IgG.

Answer 20

• Most abundant antibody in normal human serum
• Present in serum in a monomeric form (IgA)

Functions:
• Neutralisation
• Agglutination
• Complement system activation through classical pathway
• Foetal immune protection (transported across the placenta, directly into the foetal blood circulation)
• Opsonisation
•NK cells activation

Question 21

What is neutralisation?

Answer 21

A process mediated by specific antigen binding to high affinity IgG and secretory IgA antibodies which is blocking viral entry

Question 22

What does IgE do?

Answer 22

Triggers allergic responses, involves mast cells.

Question 23

Describe IgA.

Answer 23

• Second most abundant Ig type
• Present in serum in a monomeric form
• Does neutralisation
• Present in secretory fluids in dimeric form (secretory IgA, sIgA) which is good for neonatal defence (protects GI tract) and neutralisation at mucosal sites

Question 24

Describe IgD.

Answer 24

In membrane-bound monomeric form, IgD serves as a B cell antigen receptor (mediates B cell activation)

Question 25

Which antibody is a great opsonin?

Answer 25

IgG.

Question 26

How can phagocytes bind to IgG?

Answer 26

Phagocytes express an Fc receptor that binds specifically to the constant region of the heavy chain in IgG

Question 27

Which antibody is good at natural killer cell activation?

Answer 27

IgG.

Question 28

What do opsonin receptors do?

Answer 28

Opsonin receptors trap opsonised antigens in the b cell zone of lymph node. Makes it easier for b cell to bind to it.