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2.2 Transfusion Science > The Antigen-Antibody Reaction > Flashcards

The Antigen-Antibody Reaction Flashcards

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1
Q

What are the two main types of antigens

A

Allogeneic

Autologous

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2
Q

What are allogeneic antigens

A

Nonself antigens

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3
Q

What are autologous antigens

A

Self antigens

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4
Q

What are haptens

A

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

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5
Q

What are epitopes

A

Antigenic determinants that can elicit different types of antibodies

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6
Q

What exactly are antibodies

A

Glycoproteins made of 4 polypeptide chains joined by disulfide bonds

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7
Q

List the chains of an antibody

A

2 heavy chains

2 light chains (2 kappa or 2 lambda chains)

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8
Q

Name the two regions of an antibody

A

Constant region

Variable region

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9
Q

What does the constant region do?

A

Consists of heavy chains
Determines the class of antibody

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10
Q

What does the variable region do?

A

This binds to the antigen

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11
Q

Which two antibodies are we most interested in trnasfusion

A

IgM and IgG

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12
Q

What does isotype switching do?

A

Switching from one class of antibody to another

This increases the affinity of the antibody-antigen reaction

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13
Q

What may happen if a person with allergies gets a transfusion

A

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

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14
Q

Explain the process behind antibody production
(5)

A

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

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15
Q

What two things might happen when B lymphocytes are stimulated

A

They might become plasma cells and secrete antibodies

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

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16
Q

What is meant by a humoral reaction

A

Involves B lymphocytes and their antibodies

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17
Q

What are plasma cells

A

Cells that produce the majority of antibodies

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18
Q

What are memory B cells

A

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

19
Q

What two things can antibodies produced by plasma cells do?

A

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

Lyse the red cell directly

20
Q

What happens when antibodies bind to rbcs in vivo

A

Red cell breakdown

21
Q

What happens when antibodies bind to rbcs in vitro

A

Haemagglutination

22
Q

What happens when there is direct lysis of the rbcs

A

Rupture of rbc membrane (intravascular haemolysis)

Release of free haemoglobin

23
Q

What happens when haemoglobin is released from rbcs
(3)

A

Uncontrolled clotting

Hypotension

Organ failure due to poor perfusion of blood

24
Q

What happens when rbcs are coated with antibodies

A

Rbcs are sequestered in the spleen or liver and broken down

Spleen or liver may swell

Extravascular haemolysis

25
Q

What is meant by a primary response

A

IgM

Low tire

Slow response

26
Q

What is meant by secondary response

A

Rapid raise in tire

IgG

27
Q

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

A

D antigen with an immunogenicity of 50%

K antigen with an immunogenicity of 5%

28
Q

What are the two different types of antibody responses

A

Complete

Incomplete

29
Q

What is a complete antibody response

A

IgM
Antibody can agglutinate rbcs

30
Q

What is an incomplete antibody response

A

IgG

There is a slipping plane preventing antibody binding

31
Q

What is a slipping plane

A

Rbcs surrounded by a fog of positively charged ions

This gives rbcs positive charged and they repel each other

32
Q

What are the two steps involved in agglutination

A

Sensitisation

Lattice formation

33
Q

What is sensitisation

A

Antibody binds to antigen. but no visible agglutination occurs

34
Q

What is lattice formation

A

Antibody-coated cells cross-link to form visible agglutination

35
Q

What is the zeta potential

A

The electrical potential at the slipping plane

36
Q

What is the indirect antiglobulin test
(4)

A

Inject human antibodies into rabbits

Rabbit produces anti human globulins (AHGs)

This allows for cross linking of antibodies on rbcs

Agglutination will now occur

37
Q

How do we make monoclonal antibodies
(7)

A

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

38
Q

What is the equation for antigen-antibody reaction

A

The equilibrium constant/affinity K=

K = [AbAg]/[Ab][Ag]

39
Q

How are alloantibodies formed

A

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

40
Q

How are alloantibodies detected

A

An antibody screen test

41
Q

What is an antibody screen test
(5)

A

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

42
Q

What does complement do?
(2)

A

Complement proteins enhance the immunologic process when activated

Form the membrane attack complex which lyses cells

43
Q

What are the two main pathways of complement

A

Classical pathways -> activated by antibodies

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

2.2 Transfusion Science (22 decks)

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