Humoral immunity and the generation of antibody diversity Flashcards
What are the characteristics of an adaptive immune response?
triggered by exposure to microbes lag time (exposure to response) combat pathogen memory fast at eliminating better with repeated exposure
What is the structure of an antibody?
tetrameric protein (made of immunoglobin proteins)
How many chains do the antibodies have?
2 light and 2 heavy
light can either be Lambda or Kappa
What are the chains held together by?
disulphide bonds= non covalent
What region does EACH chain have?
variable and constant
What happens in the variable region?
amino acid sequence varies from one antibody to another
this variable region binds antigen
this is called the Fab region
What happens in the constant region?
responsible for effector functions such as activating complements and binding to phagocytes
phagocytes have Fc receptors which allow them to recognize organisms that have been opsonized by immunoglobulins
What receptors do phagocytes have?
Fc= bind to the constant region of the antibody
The variable region has 3 complementary determining regions. What are they?
CDR1, CDR2 and CDR3, of which CDR3 is the most variable of these regions
in the 3D structure of the antibody, these CDR regions are adjacent to each other where they will bind the antigens
the rest of the variable region is just a framework which allows the CDRs to face the antigen
How many specificities of antibodies does a human have?
Abs are very diverse (humans have q>107 specificities)
There are 5 types of heavy chains - what are they?
5 types of heavy chains: mu, gamma, alpha, delta, ellipsion (lol i think?)
What are antibody classes?
IgG (), IgM (), IgA (), IgD (), IgE ()
What are subclasses of antibodies?
IgG1, IgG2, IgG3, IgG4; IgA1; IgA2
How much does a light chain weigh?
light chains = 24kDa
How much oes a heavy chain weigh?
heavy chains = 50-70kDa
Does the body design a specific antibody to bind to a specific antigen?
no it cant
Why does the body not produce speicific antibody to specific antigen? What does it do instead?
body generates over a 100,000,000 different B cells each making a random Ig
these naïve B cells sit in the lymph nodes doing not very much
during an infection, a small number of B cells by chance will happen to have an Ig that can bind to the foreign antigen
these B cells are activated and begin to multiple, this is called clonal selection
What does clonal selection require?
requires direct involvement of CD4+ T helper cells which release cytokines to activate the cell
How are so many different Ig genes generated?
in fact no complete Ig gene is inherited
only bits of genes are inherited= CALLED gene segments
By arranging these gene segments in different combinations, many different Ig sequences can be generated
What kind of DNA does the germline Kappa chain have?
one constant region C
5 short segments called the joining segments J
35 segments called variable region segments V
C region and J region are close
V is far from C and J
Where are the endonuclease enzymes located?
in front of V
behind J
What does RAG recombinase do?
V segment and one J segment are brought together via their recognition sequences
RAG recombinase identifies their recognition sequences and cuts and removes the DNA in between these two areas
After RAG recombinase has worked, there are 2 segments left that join together. What bond joins them?
hairpin= weak bond
What does exonuclease enzyme do?
this hair pin, and in doing so will mess around (add P nucleotides) with the two ends of the segments
What does terminal deoxynucleotidyl transferase (TdT) enzyme do?
randomly adds a few nucleotides to the free ends before they are ligated together
How does TdT work?
it is worth noting that this is not done via a template, but is done entirely by adding random nucleotides at the end-these added nucleotides are called N nucleotides
What are the uses of Terminal Deoxynucleotidyl transferase (TdT)?
generates immunoglobulins
makes T cell receptor in the body
marker for acute lymphoblastic leukaemia
useful enzyme in genetic engineering and recombinant DNA work
In a kappa light chain, what is the constant region coded for by?
by the C segment of the kappa light chain gene
What is the variable region in a kappa chain coded for by?
V segment of the kappa light chain gene
What is CD3 coded by?
CDR3 which is the most variable region ofthe light chain is coded for by the junction between the V and the J segments
What is the heavy chain made up of?
1 constant C segment
45 variable V segments
6 joining J segments
20 diversity D segments
J and C close
lot of DNA between J and D
What are the endonuclease enzymes in the light chain?
RAG 1 and RAG 2
How many different possibilities of heavy chains are there?
there are 540,000 different possibilities from only 72 genes inherited
In a heavy chain, what codes for the variable region?
V gene segment codes for most of the variable region
What codes for the CDRIII part of the heavy chain?
D and J, and the junctions between V, D and J form the CDR III part of the heavy chain
How many different possibilities are there for kappa light chain?
1750
When combining heavy and light chains, how many possibilities are there?
Since there are 1750 possible different combinations for kappa light chains, and 540,000 different combinations of heavy chains, there are a total of 9,450,000,000 combinations possible
add lambda light chain and possibility doubles
Is B lymphocyte diploid or haploid?
diploid
it has 2 alleles of the Ig Heavy chain
What is allelic exclusion?
B lymphocyte is diploid and has 2 alleles for Ig Heavy chain
so basically it could make 2 diff heavy chain proteins
this doesn’t happen though= ALLELIC EXCLUSION
What is the mechanism for allelic exclusion?
when one allele successfully rearranges and starts to make heavy chain proteins
gene arrangement for 2nd allele is switched off- so cant rearrange genes to make another heavy chain
What happens if the allele making a heavy chain messes up?
If one allele makes a heavy chain, but messes it up (eg the N nucleotides inserted cause a frame shift), then the cell will not successfully make a heavy chain protein, and so the process will carry on to rearrange the second allele to have a second go of making a functional protein
What are the alleles for a cell for light chain?
it has 2 alleles for lambda and kappa
How does light chain formation work?
- cell has 2 alleles for kappa, and 2 alleles for lambda
- if the cell successfully makes a kappa light chain, the cell will not make any other light chains
- if the kappa light chain from the first allele fails, the cell will move on to the kappa light chain in the second allele.
- if this fails, the cell will move to the lambda light chain allele
- this process goes on until the cell has just one light chain
What are polycloonal B cells?
equal amounts of kappa and lambda in different re arrangement of gene segments
What happens to the B cell during malignancy?
During a malignancy of the blood (B cell leukaemia, myeloma, etc), the malignant B cell will multiply rapidly and produce only one type of kappa or lambda light chain
this can be used to diagnose cancers (as there will be a lot more of kappa than lambda, or a lot more of lambda than kappa
What are T cell receptors made up of?
T cell receptors are made up of alpha and beta chains, and they work in the same way as immunoglobulins
What is an alpha chain in a TCR made of?
•the alpha chain in a TCR is made up of VJ complexes
What is the beta chain of a TCR made of?
•the beta chain in a TCR is made up of VDJcomplexes
What does serum contain?
Serum contains substances that neutralise infectious agents => antibodies (Ab)
e.g. development of rabies vaccine (serum from immune person given to patient at risk of rabies)
What is the structure of a heavy chain?
3-4 constant (C) domains + 1 variable (VH) domain
4 constant in IgM
3 constant in IgG and other antibodies
What is the structure of a light chain?
1 constant domain and 1 variable (VL) domain
How does a variable domain cause differences between different antibodies?
amino acid sequence varies highly between different immunoglobulins
What is the antigen binding site?
Vl + Vh (light plus heavy)
What are the 2 main roles of antibodes?
Recognition of an infinite number of Ags
Effector functions
What are the effector functions of antibodies?
Via Fab= bind and neutralise Antigens
other mainly mediated by Fc region
interact with other cells= complement activation
What things have Fc receptors?
macrophages, eosinophils have Fc receptors
What is the antigen binding site?
VH and VL domains contain three hypervariable regions
hypervariable regions differ the most from one antibody to another
Why do hypervariable regions make antibodies different?
hypervariable regions correspond with protruding loops that make contact with Ag
hypervariable regions of heavy and light chain form the antigen-binding surface
hypervariable regions = complementarity-determining regions (CDR1, CDR2, CDR3)
CDR3 has the highest variability due to genetic mechanisms that ensure Ab diversity
MAKE THE SITE WHERE ANTIGENS INTERACT WITH THE ANTIBODY
What is the difference between Ig primary and tertiary structure?
primary: CDR’s separate
tertiary: CDRs adjacent
What do amino acid residues in the hypervariable regions make contact with?
with amino acid residues in the antigen
Why is more than one B cell activated and many antibodies made?
bc there are:
Multiple antigens on organism
Multiple epitopes on each antigen
More than one Ab may recognise the same epitope
How many B cells are generated randomly?
10^7-10^9 different types of B cells generated randomly
How many gene segments is Vh coded in?
VH encoded in 3 gene segments (V, D, J)
How many segments is Vl coded in?
2= VJ
How do you get antibody diversity?
gene segment recombination => Ab diversity
(random arrangement of gene segments in different combinations)
)
What are the heavy chain segments?
variable region: 45V (variable); 23D (diversity); 6J (joining)
constant region: 9C (different types of heavy chain)
What do endonucleases do?
Endonuclease cuts randomly after one D and before one J
D-J joining: the free ends are ligated together to form DJ
Endonuclease cuts randomly after one V and before DJ
V-DJ joining: the free ends are ligated together to form VDJ
What are the gene segments for kappa light chain?
Variable region: 35V (variable); 5J (joining)
1C (constant region)
What are the gene segments for lambda light chain?
λ chain gene segments: 30V (variable); 4J (joining) and
4C (constant region)
What does junctional diversity do?
Junctional diversity: increases the number of Ab generated
The enzyme terminal deoxynucleotidyl transferase (TdT) adds random nucleotides (N nucleotides) to the free ends before the joining
What is the gene segment rearrangement in B cells?
Immature B cells:
1st: successful VDJ rearrangement => heavy chain produced
2nd: successful VJ rearrangement => light chain produced
What is the gene segment rearrangement in T cells?
1st: successful VDJ rearrangement => beta chain produced
2nd: successful VJ rearrangement => alpha chain produced
Mature naïve T cells express full αβ TCR/antigen receptor
How does the adaptive immune response work?
After they finish their development they are called mature naïve B cells
They circulate in the body, blood and peripheral lymphoid organs searching for antigens
If they bind to antigen and recognise it specifically, they get activated
They proliferate
Then differentiate into plasma cells that secrete lots of antibodies= can eliminate pathogen
Once pathogen dies, number of B cells and antibodies goes down over time
If after this, exposed to same pathogen again, then you have memory cells in the body generated from the first response
These proliferate faster and generate plasma cells faster in much higher numbers
So 2nd time around you have more of everything
And then 3rd time around, you will have more memory cells enough to kill the pathogen again
Where do T lymphocytes work?
cell mediated protection
Where do B lymphocytes work?
serum
When B cells come out of the bone marrow, what do they have in their membrane?
IgM sticking out
What is the difference between IgM structure and other antibodies with regards to heavy and light chains?
The light chain only has 1 constant domain
Heavy chain in IgM has 4 constant domains
Heavy chain in IgG and other antibodies has 3 constant domains
What are hypervariable regions also known as?
hypervariable regions = complementarity-determining regions (CDR1, CDR2, CDR3)
