Antibodies

Question 1

which cells produce immunoglobulins

Answer 1

B cells

Question 2

immunoglobulins role

Answer 2

bind to microbe and prevent further infection

target microbe for phagocytosis

Provide active and passive immunity
- Passive = vaccinations (no memory as you
haven’t activated your own B
cells)

Question 3

Antibody structure

Answer 3

Basic unit comprises of 2 heavy chains + 2 light chains (κ or λ) joined by disulphide bonds

Each chain consists of
- Several Ig domain repeats
- Variable and conserved regions
- Joining and diversity (HC only) regions

Question 4

immunoglobulin classes

Answer 4

IgM (µ) - first to be produced; natural antigens in peritoneum; complement activation

IgD (δ) - naive B cell antigen recognition

IgA (α) - epithelial/mucosal immunity

IgE (ε) - helminthic parasites and immediate hypersensitivity (allergy)

IgG (γ) - secondary exposure; neonatal immunity; mediate cytotoxicity; opsonisation; complement activation

Question 5

IgA structure

Answer 5

dimer

Question 6

IgE + IgG structure

Answer 6

monomer

Question 7

IgM structure

Answer 7

pentamer

10 binding sites (high avidity) but low affinity

Question 8

avidity

Answer 8

combined strengths of all binding sites on a single antibody molecule

Question 9

affinity

Answer 9

binding strength between a single binding site

Question 10

antibody diversity

Answer 10

10^7 functional antibodies -> occurs through gene rearrangement

3 separate loci on different chromosomes

Conserved section joined at mRNA stage -> enables class switching later

Question 11

role of recombinase catalyst in antibody diversity

Answer 11

irreversible cutting and re-joining to bring together single V, D and J regions

Question 12

types of alleles

Answer 12

[from gene duplication]

V = variety
D = diversity
J = joining

heavy chain - VDJC
light chain - VJC

Question 13

Hypervariable regions / complementarity determining regions (CDRs)

Answer 13

3 regions within variable gene segment with high variable amino acid sequences (CDR1,2,3)

Combining CDRs from heavy and light chains increases diversity

Further increased by nucleotide changes at V/D/J junctions (affect CDR3)

Main antigen binding to CDR folds

Question 14

Antibody production

Answer 14

During maturation in bone marrow, B cells undergo irreversible genetic recombination

produces an antibody restricted specificity
membrane bound IgM form, then IgD

Antibody generally binds antigen with weak affinity/high avidity

Question 15

what does the activation of B cells lead to?

Answer 15

Ig class switching (G, A, E) and somatic hypermutation

become plasma cells (2000 ab/s) or memory

Question 16

what happens to the VDJ region?

Answer 16

stays constant

specificity still the same

Question 17

antigen

Answer 17

any foreign substance recognised by antibodies or T-cell receptors

large macromolecules -> lots of cross links

Question 18

what results in activation of a single B cell?

Answer 18

monoclonal antibodies

Question 19

polyclonal antibody response

Answer 19

macromolecules that activate many B cells

Question 20

how are mAB used in labs?

Answer 20

immunoblotting

ELISAs

IHC

IF

FACS

blood groups

Question 21

uses of antibodies in diagnostics

Answer 21

autoimmune diseases

bacterial/viral infections

Question 22

uses of antibodies in prevention/treatment of disease

Answer 22

vaccinations

antibody based therapies - uses of antibodies in diagnostics

Question 23

Adjuvants

Answer 23

stimulate innate immune system (creates stronger response)

Question 24

properties of mAB

Answer 24

identical

Standardise concentration for detection/treatment

Question 25

blocking antibodies

Answer 25

[binds to receptor or ligand to prevent receptor binding and activation]

Anti TNF

Anti VEGF

Herceptin

Question 26

Antibody directed enzyme pro-drug therapy (ADEPT)

Answer 26

Antibody raised against cancer cell proteins and enzyme linked

Infusion given to patient

Few hours later, cytotoxic pro-drug administered

Enzyme catalyses pro-drug to active form which kills cancer cell

Question 27

Challenges of antibody based therapy

Answer 27

Relatively quick to develop, but expensive to produce

Proteins used -> requires injection

Resistance due to mutation in target is common

Antibodies = form of immunotherapy
- Modulation of immune system can have
dramatic effects
- Anaphylactic shock = biggest problem
- Treatments decrease in effectiveness
over time

Question 28

making mAB

Answer 28

1. mouse injected with specific antigen (induces production of antibodies against antigen)
2. spleen cells removed and homogenised into cell suspension
3. cells from suspension (spleen cells) then mixed with myeloma cells
4. form hybridomas => mAB

Question 29

why are myeloma cells used to make mAB?

Answer 29

= cancerous plasma B cells

have ability to continuously grow but have lost ability to produce antibodies

Question 30

Fc mediated effects

Answer 30

Fc receptors bind to antibodies that are attached to infected cells or invading pathogens

variability in Ig class affects function:

IgG + FcR on neutrophils -> phagocytosis
IgE + Fc -> eosinophil activation + mast cell degranulation
IgG + IgM -> complement activation by binding to C1q

Question 31

antibody-dependent cellular cytotoxicity (ADCC)

Answer 31

1. antibodies bind antigens on surface of target cells
2. NK cells CD16 Fc receptors recognise cell-bound antibodies
3. cross-linking of CD16 triggers degranulation into a lytic synapse
4. tumour cell dies by apoptosis

Question 32

complement dependent cytotoxicity (CDC)

Answer 32

1. antibodies bind to membrane-surface antigens on target cell
2. multiple pathways elicit a complement cascade, where complement binds to antibody
3. binding of complement => induction of membrane attack complex
4. target cell dies of cell lysis