Anderson Lecture Flashcards
Light chains
each antibody has two identical light chains: kappa or lambda, but never both
Kappa chain genes are found on
chromosome 2
Lambda chain genes are found on
chromosome 22
Heavy chain are encoded by chromosome
14
Delta, Alpha, and Gamma all have ___ constant domains
3
M and E Abs each have ____ constant domains
4 domains
double negative T cells are found in the
subcapsular cortex region of the thymus
double positive T cells are found in the
cortex of the thymus
single positive T cells are found in the
medulla
T cells whose receptors bind self-MHC molecule lose expression of either CD4 or CD8
After clonal expansion, T cells interact with APCs and B cells simultaneously. What does this do for the B cell?
allows it to react immediately to free antigens and proliferate
how many gene recombination events are required to produce the Ig heavy chain?
what are they?
2
bringing D and J –> DJ
bringing DJ to V –> VDJ
note: intervening segments are deleted
how many gene recombination events occur to make the Ig light chain?
just one: bringing the V and J together
V+J = VJ = recombination
Promoter
the V gene promoter is brought closer to the enhancer between J and C regions
mRNA translation, L is removed as protein is transported into ER
Light chain/heavy chain assemble in ER
the light chain and the heavy chain assemble in the
ER
V segments consist of ______ # segments
30-35
J segments consist of _____# segments
5
C segment consists of ____# segments
1
what does DJ binding do
it brings the C segment in close proximity
what does VDJ binding do
it makes a transcript ready to be translated into an RNA
what happens during translation of VDJ?
the intervening segments between the VDJ and C are deleted
how are the VDJ actually attached/what order?
it’s actually DJVC
what happens to the light chain D region?
it doesnt have one
who is closer to the C segment in the light chain gene, V or J?
J
what gets made? in the light chain recombination?
VJC
Each variable region on the light chain gene has two exons
one variable exon, one variable exon
Lambda light chain genes
n =
constant region genes =
two exons associated with each gene region
n = 30
Cn = 4
Exon n = leader and variability exon
kappa light chain genes
n =
constant region genes =
two exon associated with each gene =
n = 300
Cn = 1
exon n = one leader exon, one variable exon
joining region between V and C
“three” events occur before the VJC light chain is produced
1) deletion of intervening DNA and bringing together of VJ genes
2) transcription into mRNA
3) deletion of mRNA separating VJ and C regions –> VJC RNA transcript
how does junctional diversity work?
the deletion or addition of nucleotides from VDJ segments by exonucleases at time of recombination
VDJ Recombinase
collection of enzyme, expressed in immature B and T lymphocytes
recognizes DNA sequences that flank all antigen receptor VDJ gene segments
brings elements closer together
consists of recombinase activating gene 1 and 2
RAG-1 and RAG-2
exonucleases cut DNA at the ends of segments
ligases repair the breaks
recombination switch sequence
consists of three elements….
found next to every VDJ segment
consists of a heptamer, noamer, spacer of 12/23 bp
RAG-1 and 2 bind to 12 bp and 23 bp spacer and brings the VD and DJ segments together
how many bps between heptamer and noamer
12-23 bps
TdT
terminal deoxyribonucleotidyl transferase
what does the TdT do?
takes nucleotides that are not part of germline and adds them to sites of VDJ recombination
what does the “junction” caused by TdT do specifically
it encodes the amino acids of CDR3
CDRs are short hypervariable regions of amino acids within the V regions
CDR3
one of the most variable CDRs
Isotype switching
what region constitutes the “isotype”
the Constant region
Isotype (class) switching occurs by
“switch recombination” in which DNA is deleted
what’s the big picture of isotype switching?
IgM transcript is produced first. in response to T cell signaling, the G A M E D “switch regions” are pasted onto the VDJ segment
Somatic hypermutation
only occurs in B cells: OCCURS WHEN MEMORY CELLS ARE RE-STIMULATED AND UNDERGO RAPID PROLIFERATION
where does somatic hypermutation occur?
in the germinal centers of lymphoid follicles
followed by selection of high affinity B cells who express high affinity for antigen displayed by follicular dendritic cells
what happens during somatic hypermutation?
point mutations occur in the V(L) H(L) chains that increase their affinity for the epitope = affinity maturation
affinity maturation =
point mutations occur in the V(L) H(L) chains that increase their affinity for the epitope = affinity maturation
how is somatic hypermutation “initiated” ?
cytosine bases are deaminated to uracil; repair mechanism convert back to cytosine but is error prone, introduces mutations
what happens to the CDR’s dissociation constant from the primary to the second and third exposure?
it decreases
what kind of genetic alteration do TCRs undergo?
somatic recombination
the genes coding for MHC
human leukocyte antigens (HLA antigens in people)
principle determinants for graft acceptance or rejection between individuals
MHC
who can receive grafts without activating an immune response?
monozygotic twins, that’s it
MHC can bind numerous epitopes, therefore they are called
degenerate
MHC is 1) highly polymorphic or 2) not polymorphic
1) highly polymorphic
alleles are inherited from both parents and expressed equally
where is the binding cleft
in the mature HLA cell surface protein
MHC genes are on chromosome
6
MHC alleles are
codominant
both alleles from parents are expressed
ABC what?
ABC class 1 genes; only the alpha chain is polymorphic
i. difference between individuals occur in the alpha1 and alpha2 domains ii. alpha3 is invariant and binds to CD8
RQP what?
RQP class II genes; both alpha/beta chains are polymorphic
differences between individuals occur in the alpha1/beta1 domains
CD4 binds to beta2
CD4 T cells can only respond to class II MHC molecules
Skin grafts 1-4
autographs (autologous): grafts from one place on a person to another on the same person
isographs (synergic): grafts between two identical people
allogeneic: grafts between different people
xenogeneic grafts: grafts between species
HLA typing
for grafts, which HLA genes are focused on?
HLA-A, B, DR
these loci seem to predict whether graft will be rejected
testing for tissue transplantation: what do they check for?
ABO blood type
HLA-A, B, DR
preformed Abs
crossmatching
What is a haplotype used for?
a set of alleles of linked genes present on one parental chromosome
set of genes that determine antigens but are closely linked and inherited as a unit
you would compare the haploids of the donator to the patient
