B cells and antibodies

Question 1

Where are Igs present?

Answer 1

Extracellular fluids including blood, tossue fluid and mucosal secretions.

Question 2

How to Igs mediate humoral immunity?

Answer 2

By binding to free or bound antigens.

Question 3

What is XLA?

Answer 3

X-linked agammaglobulinemia is a rare immunodeficiency where patients are deficient in B-lymphocytes and Ig production.

Question 4

Do Igs directly kill microbes or catabolise antigens?

Answer 4

No

Question 5

How do Igs lead to clearance of pathogen

Answer 5

Neutralisation, opsonisation and complement activation

Question 6

How do Igs neutralise antigens?

Answer 6

By blocking interactions with their targets

Question 7

How do Igs opsonise antigens for uptake by phagocytosis

Answer 7

Fc receptors bind to Ig Fc region, leading to phagocytosis of the Ig-antigen complexes via Fc receptors.

Question 8

Igs can activate the classical complement pathways leading to…

Answer 8

Complement mediated neutralisation and lysis
Phagocytosis via complement receptors.

Question 9

What are the two types of light chain

Answer 9

Gamma or kappa

Question 10

What is the antigen binding sites made of on the Ig?

Answer 10

CDR/hypervariable loops from the VL and VH domains.

Question 11

What forces are used for binding epitopes to Igs

Answer 11

Electrostatic interaction
H bonds
Hydrophobic interaction
VDWs forces
NOT covalent bonds

Question 12

What are the five classes of Ig?

Answer 12

IgG, IgA, IgM, IgD and IgE

Question 13

What heavy chain does IgM contain?

Answer 13

Mu

Question 14

What heavy chain does IgG contain?

Answer 14

Gamma

Question 15

What heavy chain does IgA contain?

Answer 15

Alpha

Question 16

What heavy chain does IgE contain?

Answer 16

Epsilon

Question 17

What heavy chain does IgD contain?

Answer 17

Delta

Question 18

What is the structure of IgM

Answer 18

Pentameric with 10 binding sites.
J chain promotes IgM polymerisation.
4 CH domains

Question 19

IgG structure

Answer 19

Monomeric
3 CH domains

Question 20

Isotopes of IgG

Answer 20

IgG1, IgG2, IgG3, IgG4

Question 21

Structure of IgA

Answer 21

Exists as monomer or dimer
J-chain links both monomers
3 CH domains

Question 22

Structure of IgE

Answer 22

Monomeric
4 CH domains

Question 23

What antibody is first secreted in the primary response?

Answer 23

IgM

Question 24

Where is IgM mainly confined to due to its size?

Answer 24

Vascular system

Question 25

Functions of IgM

Answer 25

Neutralisation, activation of classical complement and limits spread of microbes via blood stream

Question 26

What Ig is produced in secondary response to antigen in lymph node and spleen?

Answer 26

IgG

Question 27

What is the major antibody in human blood

Answer 27

IgG1

Question 28

Function of IgG

Answer 28

Opsonisation, activates classical complement system.

Question 29

What antibody is actively transported across placent to protect fetus in first 3-6months of gestation?

Answer 29

IgG

Question 30

Where is IgA produced and when?

Answer 30

MALT during secondary response.

Question 31

Function of IgA

Answer 31

Neutralisation of bacterial toxins, prevents microbial adhesion to epithelial. Inhibits viral infectivity.

Question 32

What is IgA poor at?

Answer 32

Opsonisation and complement activation.

Question 33

Where is IgE produced?

Answer 33

MALT

Question 34

What type of infection is IgE usually produced against

Answer 34

Helminth and other parasitic infections.

Question 35

What concentration of IgE is there in blood?

Answer 35

Low

Question 36

What is IgE bound to in blood?

Answer 36

Fc-epsilon receptors on mast cells, basophils and eosinophils.

Question 37

What antigens does IgE bind to and what happens?

Answer 37

Polyvalent antigens which cross links Fc-epsilon receptors and triggers release of inflammatory mediators.

Question 38

IgD structure

Answer 38

Monomer 3 CH

Question 39

IgD concentration in blood

Answer 39

Very low

Question 40

Function of IgD

Answer 40

Acts as antigen receptor on immature B cells, no other biological function found.

Question 41

Where are plasma cells found?

Answer 41

Secondary lymphoid tissues, can migrate back to bone marrow.

Question 42

Function of plasma B cells?

Answer 42

Secrete large amounts of Igs.

Question 43

Memory B-lymphocytes, Ig secretion amounts and response.

Answer 43

Express membrane Ig only, don't secrete Ig. Response quicker and greater in amplitude than intial response.

Question 44

How do CD4+ T-helper cells activate B-lymphocytes?

Answer 44

Cytokines and CD40/CD40L interactions.