Lect 3

Question 1

What is an example of a multivalent antigen?

Answer 1

Poliovirus – several epitopes within viral coat protein

Question 2

What is a linear and discontinuous epitope?

Answer 2

A linear antigen is a continuous sequence on a protein and a discontinuous antigen is one with gaps between aminoacids

Question 3

Besides composition what also determines whether or not an antigen will be able to bind to an antibody?

Answer 3

The antigens size and shape

Question 4

What is the difference in an immunogen and antigen?

Answer 4

An immunogen is able to generate antibody production but antigens are substance which antibodies can bind – immunogens are antigens but not all antigens are immunogens

Question 5

What is a hapten? and what is an example?

Answer 5

Small chemically defined molecules that antibodies bind – usually univalent and cannot generate antibodies or elicit response unless bound to a carrier, penicillin is an example that uses RBCs as a carrier leading to complement activation and either erythrocyte lysis or phagocytosis

Question 6

What is the criteria for an effective immunogen?

Answer 6

Foreign, molecular size (>100 kDa is stronger), chemical complexity (more complex is stronger)

Question 7

How do antigens bind antibodies?

Answer 7

Through noncovalent interactions like hydrogen bonds, VDW, or electrostatic bonds between complementary amino acid side chains

Question 8

What is affinity?

Answer 8

The strength of binding between a single epitope of an antigen and an antibody’s antigen binding site

Question 9

What is valance?

Answer 9

The number of binding sites of an antibody molecule

Question 10

What is avidity?

Answer 10

The strength of the interaction of antigen molecules with multiple epitopes with antibodies

Question 11

What are the parameters avidity is dependent on?

Answer 11

Affinity of the antibody for the eptiope, valence of both the antibody and antigen and the structural arrangement of the parts that interact

Question 12

What is cross-reaction?

Answer 12

When an antibody is able to bind a similar or shared epitope – usually weakly bound

Question 13

What is M protein?

Answer 13

A virulence factor produced by certain species of strept that are antipahgocytic –antibodies made to this protein cross react with proteins found on heart muscle and cause rheumatic fever

Question 14

What are antigen antibody complexes? and what does their formation depend on?

Answer 14

Once the antigen and antibody bind to form immune complexes – formation depends on antigen:antibody ratio and nature of antigen

Question 15

What is agglutination?

Answer 15

When molecules are bridged together – RBCs do this and become heavy and go to bottom of test tubes

Question 16

How is RBS agglutination tested?

Answer 16

Coombs test in which there is a suspension of RBCs where you add anti-IgG and if an observed precipitate is formed you have a positive test result

Question 17

What is Rh factor?

Answer 17

A protein that is critical in determining whether or not a mother’s Rh negative – in which case if the baby is Rh positive (from the father and positive is dominant) than the IgG from the mother that is crossing the placenta and can start to attack the baby’s RBCs by binding where they get their oxygen from meaning that when they are on their own when born they won’t be able to breath – they can be treated with Rho to prevent the attack

Question 18

How is Rh factor tested?

Answer 18

Take RBCs out of mother and see whether or not they bind and check for agglutinates

Question 19

When does precipitation occur?

Answer 19

When Antibody and antigen levels are at equivalence then there is a lattic formation producing a precipitate

Question 20

What segments do IG genes contain to encode for the variable portion of the antibody? and how do the segments come together? Where does this rearrangement occur?

Answer 20

Light chain – V and J
Heavy chain – V, D and J
Come together by somatic recombination (loop out to bring specific segments closer together) D binds to J to give DJ and then binds to V to give VDJ, in light chain V and J join
Only occurs in B cells

Question 21

What happens after somatic recombination at DNA level in Ig genes?

Answer 21

RNA splicing to combine constant region with VDJ regions – to give antibody molecule

Question 22

How else can you generate diversity in antibodies other than somatic recombination?

Answer 22

Generation of junctional diversity – Terminal deoxytransferase (TdT) a polymerase that does not require a template and adds random nucleotides to 3’ ends of DNA – pairing of molecules and unpaired are removed by exonucleases and filled in by ligase

Question 23

What is the last way you can generate diversity in antibodies besides somatic recombination and TdT?

Answer 23

The combinations that can be formed between kappa light chain and heavy chain and lambda light chain and heavy chain

Question 24

What is allelic exclusion?

Answer 24

Allows for generation of immunoglobulins with similar light and heavy chain combinations – due to one allele from mom and one from dad – gives homogeneous B-cell receptor with high avidity binding

Question 25

What does an immature B cell have on it’s surface? and what does it have to coexpress to mature? How do you get both at the same time?

Answer 25

IgM must coexpress IgD – alternative RNA splicing

Question 26

What determines whether an Ig is secreted or membrane bound?

Answer 26

Alternate RNA splicing

Question 27

What is class switching and how does it occur?

Answer 27

How an antibody molecules gets a different constant region yet retain its specificity - done at DNA levels by AID (Activation-induced cytosine deaminase) brings switch regions together and splices out rest – not reversible