Lecture 14-15: Antigens

Question 1

The innate immune system recognizes PAMPs what does the adaptive immune system recognize?

Answer 1

Antigens

Question 2

What is an antigen (define)

Answer 2

Any molecule that can interact with the immunoglobulin receptor of B cells or the T cell receptor

Question 3

Define immunogen

Answer 3

A molecule that induced a specific immune response

Question 4

Finish the sentence, all immunogens are…

Answer 4

Antigens

Question 5

Are all antigens immunogens?

Answer 5

No, not all antigens cause an immune response

Question 6

Define haptens

Answer 6

Small antigenic molecules that can’t produce an immune response on there own

Question 7

What molecules do a B cell respond to? The immunogens

Answer 7

Proteins»Polysaccharides»Lipids or nucleic acids

Question 8

What molecules do a T cell respond to? The immunogens

Answer 8

• Proteins, some lipids, some glycolipids

- proteins are not recognized on their own and need to have a MHC molecule attached

Question 9

What kind of immunity are B cells

Answer 9

Humoral

Question 10

What kind of immunity are T cells

Answer 10

Cell mediated

Question 11

What are the 4 properties of an antigen/immunogen?

Answer 11

1. An immunogen must be non self and the more non self it is the better response it’ll produce
2. The bigger the molecule the better the response
3. Proteins with more structure increase immunogenicity.
4. Proteins must be degraded to activate T cells so factors that affect this are; insoluble, large, L amino acids

Question 12

What is antigen tolerance?

Answer 12

Too high or too low a dose of antigens

Question 13

What is the route of administration and how does it affect the immune response?

Answer 13

Intravenous, intramuscular, intradermal etc which influences the immune response

Question 14

What are adjuvants?

Answer 14

Substances that are injected with antigens and enhance the immune response

Question 15

Review adjuvant mechanisms on paper

Answer 15

I did

Question 16

What do B and T lymphocytes recognize?

Answer 16

Small sites called epitopes

Question 17

How do B-cell epitopes work? (2)

Answer 17

• they bind the antigen directly via antibodies

- they recognize almost any antigen

Question 18

What is immunodominance

Answer 18

When not all epitopes induce a response

Question 19

What is a linear and a conformational epitope and which lymphocyte can see which?

Answer 19

• 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

Question 20

What antigens can a T cell recognize and what must be done to an antigen for a T cell to recognize it?

Answer 20

• 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

Question 21

What does it mean to be amphipathic and how does this relate to T cell antigens?

Answer 21

The peptides must be amphipathic to be recognized. Meaning they need a hydrophobic and hydrophilic region to bind to MHC and TCR respectively

Question 22

What is the agretope?

Answer 22

MHC binding site of an antigen

Question 23

What is the epitope called on a T cell?

Answer 23

TCR binding site of an antigen

Question 24

Do B cells and T cells have soluble antigens?

Answer 24

B cells do, T cells do not

Question 25

What can a B cells epitope recognize

Answer 25

Hydrophilic, sequential or conformational

Question 26

Compare linear epitopes and conformational epitopes

Answer 26

- linear epitopes are stable during protein reduction and denaturation - conformational epitopes are destroyed through reduction and denaturation

Question 27

What are antigen antibody interactions like?

Answer 27

Highly specific binding between molecules

Question 28

What is antigen-antibody specificity determined by?

Answer 28

Specificity is determined by multiple low affinity non-covalent bonds such as; - ionic bonds - hydrogen bonds - van der waals interactions - hydrophobic bonds

Question 29

Define affinity

Answer 29

It is the strength of the sum of interactions between a single antigen binding site on an antibody and a single epitope

Question 30

What is the formula for association constant Ka

Answer 30

Ka=[Ab-Ag]/[Ab][Ag], concentration of Ag-Ab complex

Question 31

What is the value of low affinity Ab-Ag binding?

Answer 31

Ka=10^4 - 10^5 M^-1

Question 32

What is the value of high affinity Ab-Ag binding?

Answer 32

Ka=10^10 - 10^11 M^-1

Question 33

How does the concentration of antigens vs antigens with antibodies work?

Answer 33

- antigens on their own diffuse equally | - antigens with antibodies diffuse equally then bind to antibodies so more antigens diffuse in

Question 34

What is avidity?

Answer 34

The strength of multiple interactions between multivalent antibody and antigen. High affinity can compensate for low affinity

Question 35

What is affinity and avidity dictated by?

Answer 35

By the Ag/Ab fit and dictated by affinity and the number of Ag/Ab bindings

Question 36

Draw what low and high affinity and avidity looks like?

Answer 36

I did

Question 37

What is antigen cross reactivity?

Answer 37

- different antigens may have the same epitope which can be bonded by the same antibody - epitopes can be different but have similar chemical properties

Question 38

What are anti-A bodies?

Answer 38

Epitopes are similar to an enzyme on A from ABO blood

Question 39

What are anti-B bodies?

Answer 39

Glycoproteins on bacteria that resemble an enzyme on the B from ABO blood

Question 40

When does precipitation occur?

Answer 40

Ag-Ab interactions result in the formation of a lattice structure which requires at least a bivalent and bivalent or polyvalent antigen

Question 41

What inhibits precipitation?

Answer 41

Excess of either antibodies or antigens

Question 42

What is the zone of equivalence?

Answer 42

The maximal precipitation that is achieved in a zone of optimal antigen and antibody concentration

Question 43

What is precipitation?

Answer 43

Like chemistry, when two soluble compounds come together to make an insoluble compound

Question 44

What are the three theories for why antibodies can bind and recognize so many antigens?

Answer 44

- selective (side chain) theory - instructional theory - two gene theory

Question 45

What was the selective side chain theory?

Answer 45

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

Question 46

What is the instructional theory?

Answer 46

The antibody takes a shape that compliments the antigens however how do you account for specificity before exposure to the antigen?

Question 47

What is two gene theory?

Answer 47

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.

Question 48

What experiment proved the two gene theory?

Answer 48

Analysis of antibody genes from cancer cells and embryonic cells demonstrated DNA differences.

Question 49

What are the gene segments that make an antibody?

Answer 49

- light chain variable region (κ, λ) | - heavy chain variable region

Question 50

What is the light chain region composed of?

Answer 50

A variable (V) and a joining (J) gene segments

Question 51

What is the heavy chain region composed of?

Answer 51

A variable (V), joining (J) and diversity (D) gene segments