The Antigen-Antibody Reaction Flashcards
What are the two main types of antigens
Allogeneic
Autologous
What are allogeneic antigens
Nonself antigens
What are autologous antigens
Self antigens
What are haptens
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
What are epitopes
Antigenic determinants that can elicit different types of antibodies
What exactly are antibodies
Glycoproteins made of 4 polypeptide chains joined by disulfide bonds
List the chains of an antibody
2 heavy chains
2 light chains (2 kappa or 2 lambda chains)
Name the two regions of an antibody
Constant region
Variable region
What does the constant region do?
Consists of heavy chains
Determines the class of antibody
What does the variable region do?
This binds to the antigen
Which two antibodies are we most interested in trnasfusion
IgM and IgG
What does isotype switching do?
Switching from one class of antibody to another
This increases the affinity of the antibody-antigen reaction
What may happen if a person with allergies gets a transfusion
They may have an allergic reaction to a food antigen in their blood
Explain the process behind antibody production
(5)
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
What two things might happen when B lymphocytes are stimulated
They might become plasma cells and secrete antibodies
They might become memory cells which respond to next exposure without stimulation by T cells
What is meant by a humoral reaction
Involves B lymphocytes and their antibodies
What are plasma cells
Cells that produce the majority of antibodies
What are memory B cells
B cells that respond rapidly to next exposure and transform into plasma cells
What two things can antibodies produced by plasma cells do?
Coat the cell with antibodies and/or complement (Sensitisation)
Lyse the red cell directly
What happens when antibodies bind to rbcs in vivo
Red cell breakdown
What happens when antibodies bind to rbcs in vitro
Haemagglutination
What happens when there is direct lysis of the rbcs
Rupture of rbc membrane (intravascular haemolysis)
Release of free haemoglobin
What happens when haemoglobin is released from rbcs
(3)
Uncontrolled clotting
Hypotension
Organ failure due to poor perfusion of blood
What happens when rbcs are coated with antibodies
Rbcs are sequestered in the spleen or liver and broken down
Spleen or liver may swell
Extravascular haemolysis
What is meant by a primary response
IgM
Low tire
Slow response
What is meant by secondary response
Rapid raise in tire
IgG
What are the two most immunogenic antigens that we need to watch out for and what % immunogenicity do they have?
D antigen with an immunogenicity of 50%
K antigen with an immunogenicity of 5%
What are the two different types of antibody responses
Complete
Incomplete
What is a complete antibody response
IgM
Antibody can agglutinate rbcs
What is an incomplete antibody response
IgG
There is a slipping plane preventing antibody binding
What is a slipping plane
Rbcs surrounded by a fog of positively charged ions
This gives rbcs positive charged and they repel each other
What are the two steps involved in agglutination
Sensitisation
Lattice formation
What is sensitisation
Antibody binds to antigen. but no visible agglutination occurs
What is lattice formation
Antibody-coated cells cross-link to form visible agglutination
What is the zeta potential
The electrical potential at the slipping plane
What is the indirect antiglobulin test
(4)
Inject human antibodies into rabbits
Rabbit produces anti human globulins (AHGs)
This allows for cross linking of antibodies on rbcs
Agglutination will now occur
How do we make monoclonal antibodies
(7)
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
What is the equation for antigen-antibody reaction
The equilibrium constant/affinity K=
K = [AbAg]/[Ab][Ag]
How are alloantibodies formed
Exposure to foreign antigens during transfusion or pregnancy may cause sensitisation, resulting in production of alloantibodies
How are alloantibodies detected
An antibody screen test
What is an antibody screen test
(5)
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
What does complement do?
(2)
Complement proteins enhance the immunologic process when activated
Form the membrane attack complex which lyses cells
What are the two main pathways of complement
Classical pathways -> activated by antibodies
Alternative pathway -> activated by foreign cell surface e.g. bacteria
