ch 4 Flashcards
where do b cells originate and begin development?
bone marrow
what organs and folicles do the b-cells go through in order. (more details in ch. 6)
Bone marrow(begin development)->secondary lymphoid organ (go through circulation) -> secondary lymphoid follicle (b-cells complete maturation and differentiation- turn into the plasma cell)
what is the difference between a immunoglobulin (b-cell receptor) and a antibody
a b-cell receptor is membrane bound and contains a trans-membrane region. there is a heavy chain in a y shape and attached to the sides are light chains. Antibodies are the secreted form of immunoglobulin and are secreted by plasma cells. therefore, they are not membrane bound. While they also have heavy chains and light chains, they are broken up into the constant and variable regions. the tip of the y shaped anitbody is the variable region (FAB) and the rest is the constant region (FC). the constant region has the effector function and is what the other cells use to identify the antibody.
how many Ag specificities does a b-cell have?
one
how is the antibody isotype determined
heavy chain name. Each isotype has its own heavy chain.
the light chains can only be what 2 things
Kappa or Lambda
what are the parts of the antibody
the variable region, constant region, hinge region and the antigen binding sites at the variable region
what does the FAB region consist of
Heavy and light chain constant region and heavy/light chain variable region and antigen binding sites
what isotype has the flexible hinge and what is the advantage?
IgG has flexible hinges that twist to bind to different antigens and helps them to reach more than one on the same organism. Meaning they can bind both their arms to an antigen.
what are the 2 isotypes that lack hinge regions
IgM and IgE. they are rigid and have longer constant regions.
what are the different antibody isotypes and what are they for/ where are they found?
IgM- the prototype (rough draft) secreted or on the cell
IgD- b-cell receptor on the cell (no secreted form always bound to the b-cell)
IgG- most common in plasma. can cross the placenta to the fetus
IgA- found in gut and secretions (mucus, milk, saliva and tears)
IgE- associated with allergies, parasites and anaphylaxis
what is the structure of the different isotypes
IgG- monomer (2 binding sites)
IgM- pentamer (10 binding sites)
IgD- monomer
IgE- monomer
IgA- dimer (4 binding sites)
what is the structural basis of antibody diversity and where are they located
the hypervariable loops located at the FAB region.
what is an epitope
the thing ( a carb or protein) on the antigen the antibodies bind to
multivalent
antigen has multiple epitopes
- same repeated
-multiple different
what helps make the variable shaped on the FAB region that the epitopes bind to
HV loops
how do you make a mouse monoclonal antibody
juice up the mouse with what you want to target. eg spike protein.
then a bunch of antibodies are made and you pick the best one by testing the binding.
you fuse them with an immortalized b cell with the mouse cell and use PEG to make an immortalized cell that keeps pumping out the best antibodies.
treat with drugs where only the hybridomas survive that pumps out the selected antibodies.
then proliferate.
what does MAB stand for
Monoclonal antibodies
What are the two types of diversity in the FAB region?
germline- inherited
somatic
what are the 2 types of somatic diveristy
recombination and junctional diveristy
recombination diversity is where the inherited genes are rearranged and junctiontional diversity happens when the genes are glued together (the coding joints)
germline diversity
Igs are all chopped up and only b cells can express them. They are arranged sequentially on the chromosomes. so the germline are inherited then the rest of the diversity is from gene rearrangement. immature b cells are the only ones that do this.
what are the chromosomes involved in creating heavy and light chain variable genes.
chromosome 14- heavy chain
chromosome 2-kappa light chain
chromosome 22- lambda light chain
What do you need to complete a heavy/ light chain?
L- leader peptide (exons/introns ready to be transcribed)
Variable region- V[D]J -undergoes somatic rearrangement
Constant region- C: exons/introns ready to be transcribed
what happens in recombination and junctional diversity?
recombination diversity- rearrangment of gene segments (300 different light chains possible and 600 different heavy chains possible)
junctional diversity- coding joints glue the V[D]J together
what are the signal sequences that flank each V[D]J sequence?
recombination signal sequences (RSSs): nonamers(9bp) and heptamers-palindrome (7bp) they are separated by 12 or 23bps
what rule prevents RSSs recombining at different lengths
the 12/23 rule. has to bind 12/23 or 23/12
where is recomination directed for the V D and J segments
Recombination is directed by RSSs: 3’ side of V gene segments
both sides [3’ and 5’] of D gene segments
5’ side of J gene segments
describe be the structure of RAG 1 complex
has 2 subunits that forms a y shape. RAG2 is on top of RAG 1. The stems bind to the nonamers and the arms bind to the heptamers. one side of the chain has a 12 bp spacer and the other one has a 23 bp spacer.
what are HVRs and what type of diversity do they do?
HVR- hyper variable regions, the loops in the variable region structure. They help bring variability to the anitgen binding sites
HVR1 and HVR2 is for recombination diversity
HVR1- junctional diversity
how is junctional diversity generated during gene rearrangment
1) the rag complex cleave the heptamers and the nonamers
2) a hairpin is formed at the cleavage sites (2 hairpins) it is dsDNA
3) the hairpins are nicked by the RAG complex
4)the dsDNA hairpin turns into ssDNA and forms p (palindromic) nucleotides
5) TdT randomly adds N-nucleotides to the empty spaces in the ssDNA
6) the ssDNA strands are paired and exonuclease comes and cleaves off the unpaired nucleotides
7) the DNA ligase and polymerase complete the coding joint (join the D to the J)
wthe complete heavy/light chain loci in order
1) leading segment
2) v region - V[D]J must undergo somatic rearrangement
3) constant region
what are the 2 antibodies expressed on a naive mature b-cell
IgM and IgG. They are expressed at the same time but alternative mRNA splicing allows them to be expressed on the same cell at the same time.
what is the co-expression RNA process
transcription starts upstream of the leader sequence and the V (VDJ). it continues through the M and D constant genes and terminates through the G genes. the MC (says it’s going to be membrane bound) region at the end forms the pAum. the primary rna sequence is spliced to produce mRNA of heavy chain of M or D. this is processed by cleaving, polyadenylation [ pAum], and splicing to remove D
what is allelic exclusion
the heavy chain genes can come from either the mom or the dad and only the gene for the heavychain from one parent is expressed
same with light chains but it is 4 light chain loci 2 from each parent. only one of each (kappa/ lambda) is expressed
what are the other proteins the immunoglobulins are associated with. the one’s that the immunoglobulins can’t signal without
Igalpha( CD-79a) and Igbeta (CD-79b)
what does CD-79 a and b do
they bind to the c Ig heavy chain region and contain intracellular signalling regions . they proliferate and differentiate signals.
are the heavy/light chains functional in an immature b-cell?
no they need to undergo gene rearrangement
are the heavy/light chains functional in an naive mature b-cell?
yes
what happens once a naive mature b-cell encounters an antigen
it undergoes clonal selection then clonal expansion (proliferates) then is differentiates into a plasma cell.
what processes require AID
isotype switching, somatic hypermutation
true or false: during mitosis the variable region mutates via POINT MUTATIONS
true
what does AID do
Activation-induced cytidine deaminase converts cytitdine to uracil during ds separation
what is the process oh somatic hypermutation
the v region genes of heavy/light chains undergo point mutations during mitosis. AID turns the cytidine residues into uracil. the uracil is removed by the dna repair machinery and replaced with a random DNA base. if the b-cell now has higher affinity it differentiates into a plasma cell (affinity maturation)
where is somatic hypermuation concentrated?
HVR
true or false: during proliferation hypermutation happens every time bc it happens during mitosis
true
what is isotype switching
changing from IgM to Ig (G, A, E)
what heavy chains have 5’ repetitive DNA
M,G,A,E
what are repetative DNA areas
the places where the isotypes are switched (switch regions)
what is the process of isotype switching
transcription happens during the active immune response. AID binds to the switching region which turns Cytidide to Uracil. Uracil is removed by UNG and the nucleotide that doesn’t have a match is excised by APE1. the nicked DNA facilitates recombination at switch regions. the nicked strands join in a bubble and is deleted. the VDJ is joined with a different C-gene isotype.
what regulates isotype switching?
cytokines
how many subclasses are there in igG and what is the one with the long hinge region?
IgG has 4 subgroups igG3 has the long hinge region
what is Ig4
a neutralization antibody that is high in people with allergies like IgE. it dampens the immune response and is ant-inflammatory. it is used s a therapeutic and has no other effector functions
What events in the b-cell life time are irreversible?
v region assembly
junctional diversity
assembly of transcriptional control elements
somatic hypermutation
isotype switching
