Chapter 4: Antibody Structure and the Generation of B-cell Diversity Flashcards
1
Q
Immunoglobulin (Ig)
A
- antibodies are of a class of glycoproteins produced by plasma cells (stimulated B-cells)
2
Q
IgM
A
- first antibody produced in blood and lymph in a primary antibody response
- 8% of Ig pool
- is a pentameric antibody
3
Q
IgG
A
- makes up the vast majority of antibody in blood lymph
- principle antibody in secondary antibody response agains an antigen
- 80% of Ig pool
- monomeric antibody
4
Q
IgA
A
- is found in the body cavities where is binds bacteria and viruses before they can infect tissue
- 12% of Ig pool
- dimeric antibody
5
Q
IgE
A
- important in allergic reactions
- trace amounts in serum
- monomeric antibodies
6
Q
IgD
A
- normally bound to B-cells as a cell receptor
- monomeric antibodies
7
Q
The Structural Basis of Antibody Diversity
A
- antibodies are composed of polypeptides with variable and constant regions
- epitope recognition requires antibodies to have a special structure of
2 identical heavy (H) chains
2 identical light (L) chains
8
Q
Each light and heavy chain has:
A
- a constant region: which determines the location and functional class of the antibody
- a variable region: which contains different amino acids for the many antibodies produced
- an antigen-binding site is formed from the hypervariable regions of a heavy-chain V domain and a light V domain
- the variability formation of the specific antigen binding site
9
Q
Immunoglobulin chains are folded into compact and stable protein domains held together by….
A
- disulfide bonds
10
Q
Treatment of IgG with the enzyme papain results in…
A
- proteolytic cleavage of the hinge of each heavy chain and reduction of the disulfide bonds that connect the two hinges
11
Q
Flexible Hinge
A
- on the IgG molecule allows it to bind with both arms to many different arrangements of antigens on the surfaces of pathogens
12
Q
IgG antibody is made up of…
A
- two identical heavy chains and two identical light chains
13
Q
Epitopes can bind to…
A
- pockets, grooves, extended surfaces, or knobs in antigen-binding sites
- antigen binding sites vary in shape and physical properties
14
Q
Linear Epitope
A
- formed from contiguous amino acids
15
Q
Discontinuous Epitope
A
- formed from amino acids from different parts of the polypeptide that are brought together when the chain folds
16
Q
Monoclonal Antibodies
A
- produced from a clone of antibody-producing hybridoma cells
- used to treat a variety of diseases
Rituxan: anti-CD20 and cell killing by ab/compliment
Adalimumab: blocker of anti-TNF-alpha
17
Q
Production of a mouse monoclonal antibody
A
- lymphocytes from a mouse are immunized with antigen are fused with myeloma cells by using polyethyleneglycol
18
Q
Myelomas
A
- tumors of plasma cells used to make hybridomas
- hybridomas only express the antibody made by the B-cell partner
19
Q
Before you get infected…
A
- generation of immunoglobulin diversity in B cells before encounter with antigen
20
Q
Gene Rearrangement
A
- the DNA sequence encoding a V region is assembled from two or three gene segments
21
Q
Two type of gene segment that encode the light-chain V region are called…
A
- variable (V)
- joining (J)
22
Q
Two light-chain loci versions
A
- kappa or lambda, only one is used
23
Q
Heavy-chain locus includes…
A
- an additional set of diversity (D) gene segments for a total of 3 segments
24
Q
Random Somatic Recombination of gene
A
- diversity in the antigen-binding sites of immunoglobulins
- enzymes responsible for recombining are V, D, and J
- also called V(D)J recombinase
25
RAG Complex
- recombination activating gene
| - gene segments encoding the VARIABLE region are joined by recombination at recombination sequences recognized by RAG
26
Alternative mRNA Splicing
- developing and naive B cells use this to make both IgM and IgD
- these B cells have not been yet activated by the antigen
27
The Isotype of an antibody is determined...
- by its heavy chain
- only heavy chains made by mature B cells before they encounter antigen are mu and delta corresponding to IgM and IgD, respectively, on B cell surfaces
28
Differential Splicing (no gene arrangement)
- simultaneous expression by both forms from the same heavy chain locus is accomplished by differential splicing of the same primary RNA transcript
29
Each B cells produces...
- immunoglobulin of a single antigen specificity
Allelic Exclusion
B cells are mono specific
30
Allelic Exclusion
- in developing B-cells ensures that only one heavy chain and one light chain are expressed, which results in B cells producing antibodies of a single antigen specificity
31
B cells are Monospecific
- an encounter with a given pathogen engages a subset of B cells that will make antibodies that bind only to that pathogen
- this is clonal selection
- focus of B-cell/antibody response to a specific antigen
32
Immunoglobulin is first made...
- in a membrane-bound form that is present on the B-cell surface
- when B cells first make IgM and IgD, they are associated with the cell membrane
- they need anchors to stick to the plasma membrane
33
Two anchors of a receptor
- IgB (beta) and Iga (alpha)
- are invariant chains which are transmembrane proteins that anchor the antibody heavy chain, constant region, to the plasma membrane
34
Diversification happens...
- after you get sick
| - antibodies are produces after B cells encounter antigen
35
Secreted antibodies are produced...
- by an alternative pattern of heavy-chain RNA processing
36
Gene rearrangement in immune B cells leads to the expression of...
- a functional heavy and light chain and to the production of membrane-bound IgM and IgD on the mature B cells
37
After and encounter with antigen...
- the secreted antibodies are produced by the B cell (now known as the plasma cell)
Alternative RNA Splicing (no gene arrangement)
- membrane bound has a hydrophobic anchor sequence at the end of the heavy chain, where the secreted on has a hydrophilic one
38
Secreted IgM is in a ________ shape
- pentamer
39
Somatic Hypermutation
- rearranged V-region sequences are further diversified
- once a B cell has been activated by antigen, further diversification of the whole of the V-domain coding sequences occurs
40
There is a random point mutation...
- at a very high rate throughout the V-region of the heavy and the light chain genes
- constant regions are not effected
41
Activation-Induced Cytidine Deaminase (AID)
- somatic hyermutation results in B cell bearing mutant antibodies at the variable region
- dependent on the enzyme
- some of these mutant antibodies will bind antigen better (higher affinity)
- B cells containing these mutant receptors will compete for the antigen and are preferentially selected to mature in plasma cells
42
Improved Antigen-Binding Sites
- the almost random variation produced by somatic hypermutation allows selection of variant immunoglobulins with improved antigen-binding sites
43
Isotype switching produces...
- immunoglobulins with different C regions but identical antigen specificities
- only occurs in B-cells that have been activated
44
Activation-induced Cytidine Deaminase (AID)
- like somatic hypermutation, isotype switching (or class switching) is dependent on this enzyme
45
C regions
- further DNA recombination allows V regions to be joined with different C regions
46
Antibodies with different C regions have...
- different effector functions
| - produced by plasma cells (stimulated B-cells)
