Lectures 19, 20, 21: Antigen Recognition by Lymphocytes Flashcards
The BCR is compreised of ___(#) polypeptide chains, what are these chains?
4; 2 identical light chains and 2 identical heavy chains
the chains of the BCR are connected by ____ bonds
disulphide
what are the 2 types of light chains for the BCR?
lambda and kappa
light chains have ___(#) variable regions and ___(#) constant regions
1 and 1
heavy chains of BCR have __(#) variable regions and ___(#) constant regions
1; 3-4
there are multiple types of BCR heavy chains and they are defined by their ____ regions
constant
The TCR is made of ___(#) polypeptide chains which are linked by ____ bonds
2; disulphide
what are the 2 types of TCR?
- alpha/beta heterodimer
2. gamma/delta heterodimer
how many variable and constant regions does each TCR polypeptide have
1 constant and 1 variable region each
what are the 2 important fundamental differences between TCR and BCR?
- T cells do not secrete TCR while B cells do secrete immunoglobulin
- TCR is not specific for native or intact antigen, instead, antigen must be presented by self MHC
what are the receptor associated molecules for BCR?
Ig-alpha and Ig-beta
what is the receptor associated molecule of TCR
CD3
in an antibody, which terminus is the variable region and which is the constant region?
variable: amino
Constant: carboxyl
what are the 2 proposed models of antibody diversity?
- Germ-line theory
2. Somatic-variation theory
explain the germ-line theory
proposed there was a different gene for each immunoglobulin
explain the somatic variation theory of antibody diversity
proposed that the genome has few genes but that recombinations or mutations result in diversity
the same CH of CL region can be connected to millions of different ___ or ___ regions
VH or VL
the same VH region can be connected to different ___ regions
CH
in 1976, Tonegawa and Hozumi found direct evidence that separate genes encode the ___ and ___ regions of immunoglobulins
V and C
there are multiple ___ for each segment type (V,D,J) in the germ-line genome
gene segments
what is the only immunoglobulin to contain D regions?
IgH
what is a signal peptide?
sometimes called a signal sequence or leading sequence or leader peptide; a short peptide at the N-terminus of most new proteins that are destined for the secretory pathway
signal peptides are usually ___ AA long
5-30
t/f multiple gene segments recombine to form the final V region and this contributes to the diversity of the final antigen binding site
t
does the final assembled VJ or VDJ region recombine with the constant region exons?
no
all heavy region constant domain exons are on ____ (different/the same) chromosomes downstream of the ____ region gene segments
the same; V,D &J
what flags the site for recombinations?
specific sequence motifs
what are RSS (recombination signal sequences)
sequences that flank teh coding regions of the gene segments
in the variable regions, there are __(#) different RSS’s
2
in the variable region, the RSSs have _____ heptamers and nonamers spaced by variable sequences of ____ to ___ (#) base pairs length
conserved palindromic; 12-23
what is the V(D)J recombinase?
a multimolecular complex that includes lymphocyte-specific recombination activation gene products (RAG1 and RAG2)
RAG1/2 and HMGB1/2 bind to the ____ and catalyse synapse formation between __ and __ gene segments
RSS; V & J
RAG binding to the RSS lead to a ____ coding end
hairpin
what are the 5 main steps of variable region recombination?
- RAG binds RSS, leading to hairpin coding end which gets cleaved
- P nucleotide additions
- Exonuclease trimming
- N nucelotide additions
- ligation of the DNA (coding & signal joints)
what 5 mechanisms contribute to the generation of antibody diversity in variable region recombination?
- multiple gene segments (combinations)
- palindromic (P) nucleotide additions
- exonuclease trimming
- non-templated (N) nucleotide addition
- combinatorial diversity (two chains combining into one antigen binding site)
particular regions in the V regions, called ____ directly contact the antigen
complementarity dertermining regions (CDR)
CDR3 includes the site of the ___ gene segment recombinations
V(D)J
after binding antigen, the V region CDR* can undergo mutations at a rate higher than typical in the genome, called _____
somatic hypermutation
can somatic hypermutation contribute to diversity of the variable region?
yes, but in a subtle way
by the end of variable region recombinations, the average affinity of antigen-specific BCRs and antibodies formed at the end of an immune response is much ____(higher/lower) than at the beginning
higher
the net increase in Ig affinity among a population of B cells is called ____
affinity selection
RNA splicing and polyadenylation signals guide the final mRNA of the ___ and ____ chain products
mu (IgM) and delta (IgD)
the simultaneous expression of IgM and IgD on B cells is due to ____
alternative splicing of the mu or delta constant region exons
what is class switch recombination?
AKA isotype class switching: chaning the constant region segments
is the mechanism of class switch recombination the same as the mechanism behind variable region gene segment recombination?
no
class switch recombination uses ___ regions and ___
switch; activation induced cytodine deaminase (AID)
what are switch regions that are used in CSR?
they are highly repetitive DNA stretches 5’ of the constant domain exons
what isotype(s) is made in response to IL-4?
IgG1 and IgE
what isotype(s) are produced in response to TGF beta?
IgA and IgG2b
what isotypes are produced in response to IL-5?
IgA
what isotypes are made in response to IFN-gamma?
IgG3 and IgG2a
is cytokine alone enough to promote CSR?
no, the B cell must also receive signal through CD40 or TLRs
the gene segments of the T cell antigen receptor are fundamentally similar with some exceptions
t
in the T cell receptor, there are multiple gene segments for each ____ region
V(D)J
one difference in TCR from BCR is that the RSS of the TCR are arranged in a manner that permits multiple __ region use
D
the TCR having its RSSs arranged in a way that permits multiple D region use is called ___
alternative joining of D segments
what are S switch regions?
long stretches of G/C rich DNA with internal repeats, each switch region exon has unique repeats
on B cells, are the variable regions of the light chains the same as the variable regions of the constant regions?
no
t/f each AA loop is usually an exon
t
would you ever see a kappa and lambda light chain on the same B cell receptor?
no (would always be two lambda or two kappa)
in what step is it decided if the antibody will be secreted?
during alternative splicing
if an antibody has a membrane spanning unit, what is its fate? What if it does not have this?
membrane bound = will remain on the surface of B cell; if not, it will be secreted
do T cells secrete their receptors?
no
do TCR have alternative splicing?
no
light chain and heavy chains only rearrange in __ cells
B
every kappa chain your B cells make will have the same ________ region
constant
it is critical that recombinations occur in a way that preserves the ____ to make a V region
open reading frame
if recombinations do not preserve an open reading frame, what happens to the B cell?
undergoes apoptosis
in the heavy chain of B cells, why do the D regions have RSS on both sides?
bc they need to rearrange with both J and V at up and downstream
can D chains recombine with each other?
no
recombination can only occur between RSSs of ____(the same/different) lengths
different
what is a palindrome?
read the same backwards and forwards
