The Antigen-Antibody Reaction

Question 1

What are the two main types of antigens

Answer 1

Allogeneic

Autologous

Question 2

What are allogeneic antigens

Answer 2

Nonself antigens

Question 3

What are autologous antigens

Answer 3

Self antigens

Question 4

What are haptens

Answer 4

Partial antigens that require a carrier molecule to elicit an immune response

They are too small to cause a reaction on their own -> they must be combined with something bigger e.g. vaccines

Question 5

What are epitopes

Answer 5

Antigenic determinants that can elicit different types of antibodies

Question 6

What exactly are antibodies

Answer 6

Glycoproteins made of 4 polypeptide chains joined by disulfide bonds

Question 7

List the chains of an antibody

Answer 7

2 heavy chains

2 light chains (2 kappa or 2 lambda chains)

Question 8

Name the two regions of an antibody

Answer 8

Constant region

Variable region

Question 9

What does the constant region do?

Answer 9

Consists of heavy chains
Determines the class of antibody

Question 10

What does the variable region do?

Answer 10

This binds to the antigen

Question 11

Which two antibodies are we most interested in trnasfusion

Answer 11

IgM and IgG

Question 12

What does isotype switching do?

Answer 12

Switching from one class of antibody to another

This increases the affinity of the antibody-antigen reaction

Question 13

What may happen if a person with allergies gets a transfusion

Answer 13

They may have an allergic reaction to a food antigen in their blood

Question 14

Explain the process behind antibody production
(5)

Answer 14

Antigens are processed and presented to T Cells by Antigen presenting cells e.g. dendritic cells

APCs present the antigenic epitopes as small peptides

T cells produce cytokines in response

Cytokines signal B lymphocytes to convert to plasma cells

Plasma cells then secrete antibodies with a specificity for the stimulating antigen

Question 15

What two things might happen when B lymphocytes are stimulated

Answer 15

They might become plasma cells and secrete antibodies

They might become memory cells which respond to next exposure without stimulation by T cells

Question 16

What is meant by a humoral reaction

Answer 16

Involves B lymphocytes and their antibodies

Question 17

What are plasma cells

Answer 17

Cells that produce the majority of antibodies

Question 18

What are memory B cells

Answer 18

B cells that respond rapidly to next exposure and transform into plasma cells

Question 19

What two things can antibodies produced by plasma cells do?

Answer 19

Coat the cell with antibodies and/or complement (Sensitisation)

Lyse the red cell directly

Question 20

What happens when antibodies bind to rbcs in vivo

Answer 20

Red cell breakdown

Question 21

What happens when antibodies bind to rbcs in vitro

Answer 21

Haemagglutination

Question 22

What happens when there is direct lysis of the rbcs

Answer 22

Rupture of rbc membrane (intravascular haemolysis)

Release of free haemoglobin

Question 23

What happens when haemoglobin is released from rbcs
(3)

Answer 23

Uncontrolled clotting

Hypotension

Organ failure due to poor perfusion of blood

Question 24

What happens when rbcs are coated with antibodies

Answer 24

Rbcs are sequestered in the spleen or liver and broken down

Spleen or liver may swell

Extravascular haemolysis

Question 25

What is meant by a primary response

Answer 25

IgM Low tire Slow response

Question 26

What is meant by secondary response

Answer 26

Rapid raise in tire IgG

Question 27

What are the two most immunogenic antigens that we need to watch out for and what % immunogenicity do they have?

Answer 27

D antigen with an immunogenicity of 50% K antigen with an immunogenicity of 5%

Question 28

What are the two different types of antibody responses

Answer 28

Complete Incomplete

Question 29

What is a complete antibody response

Answer 29

IgM Antibody can agglutinate rbcs

Question 30

What is an incomplete antibody response

Answer 30

IgG There is a slipping plane preventing antibody binding

Question 31

What is a slipping plane

Answer 31

Rbcs surrounded by a fog of positively charged ions This gives rbcs positive charged and they repel each other

Question 32

What are the two steps involved in agglutination

Answer 32

Sensitisation Lattice formation

Question 33

What is sensitisation

Answer 33

Antibody binds to antigen. but no visible agglutination occurs

Question 34

What is lattice formation

Answer 34

Antibody-coated cells cross-link to form visible agglutination

Question 35

What is the zeta potential

Answer 35

The electrical potential at the slipping plane

Question 36

What is the indirect antiglobulin test (4)

Answer 36

Inject human antibodies into rabbits Rabbit produces anti human globulins (AHGs) This allows for cross linking of antibodies on rbcs Agglutination will now occur

Question 37

How do we make monoclonal antibodies (7)

Answer 37

Mice immunised with antigen Spleens harvested for immune cells Fusion with tumour cells forms hybridomas Hybridomas are cultured and grown Hybridomas are screened for the production of desired antibody Each hybridoma is descended from a single B-cell clone Hybridoma cell line is expanded and makes the same antibody molecule

Question 38

What is the equation for antigen-antibody reaction

Answer 38

The equilibrium constant/affinity K= K = [AbAg]/[Ab][Ag]

Question 39

How are alloantibodies formed

Answer 39

Exposure to foreign antigens during transfusion or pregnancy may cause sensitisation, resulting in production of alloantibodies

Question 40

How are alloantibodies detected

Answer 40

An antibody screen test

Question 41

What is an antibody screen test (5)

Answer 41

A test used to detect alloantibodies before transfusion Checks for non ABO antibodies We use group O cells -> there is no antibodies in the serum Everything will be fine once we detect the antibodies -> we just won't give them the product with the antigen Some conditions such as sickle cell anaemia -> any inflamed state -> the immune system is switched on -> they will tend to produce more antibodies

Question 42

What does complement do? (2)

Answer 42

Complement proteins enhance the immunologic process when activated Form the membrane attack complex which lyses cells

Question 43

What are the two main pathways of complement

Answer 43

Classical pathways -> activated by antibodies Alternative pathway -> activated by foreign cell surface e.g. bacteria