Lecture 14-15: Antigens Flashcards
The innate immune system recognizes PAMPs what does the adaptive immune system recognize?
Antigens
What is an antigen (define)
Any molecule that can interact with the immunoglobulin receptor of B cells or the T cell receptor
Define immunogen
A molecule that induced a specific immune response
Finish the sentence, all immunogens are…
Antigens
Are all antigens immunogens?
No, not all antigens cause an immune response
Define haptens
Small antigenic molecules that can’t produce an immune response on there own
What molecules do a B cell respond to? The immunogens
Proteins»Polysaccharides»Lipids or nucleic acids
What molecules do a T cell respond to? The immunogens
- Proteins, some lipids, some glycolipids
- proteins are not recognized on their own and need to have a MHC molecule attached
What kind of immunity are B cells
Humoral
What kind of immunity are T cells
Cell mediated
What are the 4 properties of an antigen/immunogen?
- An immunogen must be non self and the more non self it is the better response it’ll produce
- The bigger the molecule the better the response
- Proteins with more structure increase immunogenicity.
- Proteins must be degraded to activate T cells so factors that affect this are; insoluble, large, L amino acids
What is antigen tolerance?
Too high or too low a dose of antigens
What is the route of administration and how does it affect the immune response?
Intravenous, intramuscular, intradermal etc which influences the immune response
What are adjuvants?
Substances that are injected with antigens and enhance the immune response
Review adjuvant mechanisms on paper
I did
What do B and T lymphocytes recognize?
Small sites called epitopes
How do B-cell epitopes work? (2)
- they bind the antigen directly via antibodies
- they recognize almost any antigen
What is immunodominance
When not all epitopes induce a response
What is a linear and a conformational epitope and which lymphocyte can see which?
- linear is when there isn’t any two lines touching just one single line
- conformational is when two lines intersect
- B cells can see both
- T cells can only see one
What antigens can a T cell recognize and what must be done to an antigen for a T cell to recognize it?
- only protein and some glycolipids
- antigen has to be processed
- antigens peptide fragments must be presented in association with major histocompatibility complex molecules
- peptide must be amphipathic
What does it mean to be amphipathic and how does this relate to T cell antigens?
The peptides must be amphipathic to be recognized. Meaning they need a hydrophobic and hydrophilic region to bind to MHC and TCR respectively
What is the agretope?
MHC binding site of an antigen
What is the epitope called on a T cell?
TCR binding site of an antigen
Do B cells and T cells have soluble antigens?
B cells do, T cells do not
What can a B cells epitope recognize
Hydrophilic, sequential or conformational
Compare linear epitopes and conformational epitopes
- linear epitopes are stable during protein reduction and denaturation
- conformational epitopes are destroyed through reduction and denaturation
What are antigen antibody interactions like?
Highly specific binding between molecules
What is antigen-antibody specificity determined by?
Specificity is determined by multiple low affinity non-covalent bonds such as;
- ionic bonds
- hydrogen bonds
- van der waals interactions
- hydrophobic bonds
Define affinity
It is the strength of the sum of interactions between a single antigen binding site on an antibody and a single epitope
What is the formula for association constant Ka
Ka=[Ab-Ag]/[Ab][Ag], concentration of Ag-Ab complex
What is the value of low affinity Ab-Ag binding?
Ka=10^4 - 10^5 M^-1
What is the value of high affinity Ab-Ag binding?
Ka=10^10 - 10^11 M^-1
How does the concentration of antigens vs antigens with antibodies work?
- antigens on their own diffuse equally
- antigens with antibodies diffuse equally then bind to antibodies so more antigens diffuse in
What is avidity?
The strength of multiple interactions between multivalent antibody and antigen. High affinity can compensate for low affinity
What is affinity and avidity dictated by?
By the Ag/Ab fit and dictated by affinity and the number of Ag/Ab bindings
Draw what low and high affinity and avidity looks like?
I did
What is antigen cross reactivity?
- different antigens may have the same epitope which can be bonded by the same antibody
- epitopes can be different but have similar chemical properties
What are anti-A bodies?
Epitopes are similar to an enzyme on A from ABO blood
What are anti-B bodies?
Glycoproteins on bacteria that resemble an enzyme on the B from ABO blood
When does precipitation occur?
Ag-Ab interactions result in the formation of a lattice structure which requires at least a bivalent and bivalent or polyvalent antigen
What inhibits precipitation?
Excess of either antibodies or antigens
What is the zone of equivalence?
The maximal precipitation that is achieved in a zone of optimal antigen and antibody concentration
What is precipitation?
Like chemistry, when two soluble compounds come together to make an insoluble compound
What are the three theories for why antibodies can bind and recognize so many antigens?
- selective (side chain) theory
- instructional theory
- two gene theory
What was the selective side chain theory?
Antibodies express multiple side chains of various antigen specificity and when an antigen interacts with a side chain more of the side chains are made. It can be disproved however
What is the instructional theory?
The antibody takes a shape that compliments the antigens however how do you account for specificity before exposure to the antigen?
What is two gene theory?
Two genes encode the antibody, one for the variable region and one for the constant region. Many different variable genes which accounts for the diversity produced and only a few constant genes.
What experiment proved the two gene theory?
Analysis of antibody genes from cancer cells and embryonic cells demonstrated DNA differences.
What are the gene segments that make an antibody?
- light chain variable region (κ, λ)
- heavy chain variable region
What is the light chain region composed of?
A variable (V) and a joining (J) gene segments
What is the heavy chain region composed of?
A variable (V), joining (J) and diversity (D) gene segments
