Antibodies

Question 1

Naive B cells

Answer 1

cells that have not met antigen, circulate from blood into peripheral lymphoid tissues (main site on antigen encounter)

Question 2

tell me about the structure of lymph nodes

Answer 2

cortex and inner medula

• Cortex has an outer section of B cells organised into follicles
• a paracortical area of T cells and dendritic cells
• Germinal Centres of B cell proliferation form during an immune response
• Medulla consists of macrophages and antibody secreting B cells (Plasma cells)
• Antigen (in DC) enter through afferent lymphatics.

Question 3

red pulp of the spleen

Answer 3

site of RBC destruction

Question 4

white pulp of the spleen

Answer 4

White pulp is lymphoid

Question 5

pathway through the spleen

Answer 5

• Blood carrying lymphocytes
  and antigen enter from a trabecular artery into a central arteriole
• they pass into a marginal sinus and exit through a trabecular vein

Question 6

marginal sinus

Answer 6

surrounded by lymphocytes, and within it is the periarteriolar sheath (PALS), made up of T cells
B cell follicles and a B cell corona also form. Important - antigen enters from blood rather than lymph.

Question 7

key features of adaptive immune response

Answer 7

antigen specificity, and memory
the secondary (memory) response is faster, can produce more antibody, and does not prevent you from making a response to another antigen (multiple antigens -vaccination)

Question 8

Antibodies can be expressed as

Answer 8

membrane bound (B cell receptor - BCR) or secreted forms.
B cells express a single Ab specificity only

Question 9

what are the functions of Ab cells

Answer 9

• firstly to bind the pathogen that elicited its production

- secondly to recruit other cells and molecules that will lead to clearance or destruction of the pathogen

Question 10

Ab structure

Answer 10

• made of four polypeptide chains, two identical heavy (H) chains and two identical light chains (L)
• The H chains are disulfide bonded to each other, and each H chain is also disulfide bonded to a L chain

Question 11

two types of L chain

Answer 11

lamba (!) and kappa (“). Any individual Ab has either ! or “, never a mixture of each. In human the ratio is 2:1 in favour of “.
Two identical H and L chains results in two identical binding sites.

Question 12

Crystal structure of antibody shows a Y shape consisting of three globular domains

Answer 12

VL - variable light, CL - constant light, VH - variable heavy, CH1 - constant heavy 1

Question 13

Proteolytic digestion reveals

Answer 13

functional domains of Ab

Question 14

The binding site for antigen

is contained where

Answer 14

in the Fab region whilst The Fc region performs many of the functions of Ab, interacting with receptors etc

Question 15

what can be used to label cells

Answer 15

Fab and F(ab)2 fragments
are very us in the lab without inducing the effects
of the Fc region, or in the case of Fab fragments, inducing receptor triggering or internalisation by crosslinking

Question 16

Hypervariability in V domains

Answer 16

• Three hypervariable loops determine antigen specificity by forming a surface complimentary to the antigen.
• Final specificity is determined by a combination of loops from H and L chains, and not either alone.

Question 17

Antigen binding to Ab

Answer 17

Antigens can bind in pockets or grooves, or on extended surfaces

Question 18

antibody repertoire

Answer 18

The total number of antibody specificities available in an individual
humans its = 10’11

Question 19

Germline Theory

Answer 19

suggested that a separate gene existed for each Ab. Not really the case.

Question 20

Somatic Diversification theory

Answer 20

proposed that repertoire is generated from a limited number of V region genes that undergo alteration. Essentially correct.

Question 21

Chromosomal Rearrangement

Answer 21

The sequence of a V region is generated by the somatic recombination of separate gene segments

Question 22

Junctional Diversity

Answer 22

N-nucleotides, (non template-encoded) are added by terminal deoxynulceotidyl transferase (TdT).
After upto 20 nucleotides are added, pairing is attempted, followed by trimming off nonmatching bases, filling gaps and ligation to complete.

Question 23

• Ab diversity is created by

Answer 23

• 1 -rearranging multiple gene segments
• 2 - junctional diversity
• 3 - different combinations of H and L chains
• All the above happen during B cell development, long before it ever sees antigen

Question 24

Somatic Hypermutation

Answer 24

occurs after B cells have become antigen activated in the lymph node.

Question 25

affinity maturation.

Answer 25

During the course of an immune response mutations accumulate in the V regions of the H and L chain genes. Some of these will bind antigen better and these cells are selected to expand and secrete antibody

Question 26

Five classes of Ab

Answer 26

IgM
IgG
IgD
IgA
IgE

Question 27

Cell surface IgM

Answer 27

All B cells initially express a membrane form of IgM (some also IgD). After antigen stimulation they can secrete a soluble version of the same IgM made by alternative mRNA processing

Question 28

what supplies functional diversity

Answer 28

Cells also undergo isotype switching, where the IgM Heavy chain is swapped for IgG etc

Question 29

Antibody multimers

Answer 29

IgM can be secreted as pentamers, IgA as dimers. Both involve an additional J chain in this process.

Question 30

Selective distribution of Ab isotypes in body.

Answer 30

IgG and IgM predominate in plasma.
IgG and monomeric IgA are the main isotypes in extracellular fluid.
Dimeric IgA predominates in secretions across epithelia, including breast milk.
The fetus receives IgG by transplacental transfer.
IgE is found mostly near to epithelial Surfaces, especially gut, lungs and skin.
The brain is normally free from Ab.

Question 31

high levels of Ab-Ag

Answer 31

high levels of Ab-Ag complexes are prevalent in some autoimmune disease, major cause of glomerulonephritis

Question 32

Infliximab

Answer 32

anti-Tumour Necrosis Factor (inflammatory mediator). Used in Rheumatoid Arthritis, Ankylosing Spondylitis, psoriasis, inflammatory bowel diseases.

Question 33

Herceptin

Answer 33

anti HER2 (human epidermal growth factor receptor 2) . Can block growth and lead to destruction of breast tumour cells that express high levels of HER2.

Question 34

Gleevac

Answer 34

anti-tyrosine kinase. Effective against Chronic Myeloid Leukemia.