Lect 3 Flashcards
What is an example of a multivalent antigen?
Poliovirus – several epitopes within viral coat protein
What is a linear and discontinuous epitope?
A linear antigen is a continuous sequence on a protein and a discontinuous antigen is one with gaps between aminoacids
Besides composition what also determines whether or not an antigen will be able to bind to an antibody?
The antigens size and shape
What is the difference in an immunogen and antigen?
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
What is a hapten? and what is an example?
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
What is the criteria for an effective immunogen?
Foreign, molecular size (>100 kDa is stronger), chemical complexity (more complex is stronger)
How do antigens bind antibodies?
Through noncovalent interactions like hydrogen bonds, VDW, or electrostatic bonds between complementary amino acid side chains
What is affinity?
The strength of binding between a single epitope of an antigen and an antibody’s antigen binding site
What is valance?
The number of binding sites of an antibody molecule
What is avidity?
The strength of the interaction of antigen molecules with multiple epitopes with antibodies
What are the parameters avidity is dependent on?
Affinity of the antibody for the eptiope, valence of both the antibody and antigen and the structural arrangement of the parts that interact
What is cross-reaction?
When an antibody is able to bind a similar or shared epitope – usually weakly bound
What is M protein?
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
What are antigen antibody complexes? and what does their formation depend on?
Once the antigen and antibody bind to form immune complexes – formation depends on antigen:antibody ratio and nature of antigen
What is agglutination?
When molecules are bridged together – RBCs do this and become heavy and go to bottom of test tubes
How is RBS agglutination tested?
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
What is Rh factor?
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
How is Rh factor tested?
Take RBCs out of mother and see whether or not they bind and check for agglutinates
When does precipitation occur?
When Antibody and antigen levels are at equivalence then there is a lattic formation producing a precipitate
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?
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
What happens after somatic recombination at DNA level in Ig genes?
RNA splicing to combine constant region with VDJ regions – to give antibody molecule
How else can you generate diversity in antibodies other than somatic recombination?
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
What is the last way you can generate diversity in antibodies besides somatic recombination and TdT?
The combinations that can be formed between kappa light chain and heavy chain and lambda light chain and heavy chain
What is allelic exclusion?
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
