B Cells 3 Flashcards
what is the shape of an antibody?
Y
what type of molecule are antibodies?
glycoproteins
what is immunoglobulin?
protein family that antibodies and BCRs are part of
describe the structure of antibody in terms of chains
- 2 identical disulfide-linked heavy chains
- 2 identical light chains
describe the structure of antibody in terms of regions
VARIABLE regions –> heavy and light chains both have a variable region for antibody binding (V_L, V_H)
CONSTANT regions –> heavy and light chains both have a constant region (C_L, C_H)
what is the function of the variable region?
Ag binding
how many variable regions are there in an antibody?
2 identical variable regions –> therefore 2 identical binding sites
what does Ag binding lead to?
neutralization
what is the function of the constant region?
involved in complement activation
what is the constant region called?
Fc
what does the constant region do? and 2 functions
Fc binds Fc receptors on phagocytes and other cell types to lead to intracellular signaling
- C1q binds to activate complement
- help mast cells get rid of helminth
- opsonization for phagocyte
what are the 2 fragments of antibody?
- Fab fragments
- Fc fragments
how many Fab fragments per antibody?
2
what does Fab stand for?
Fragment antigen binding
what parts of the antibody are in Fab fragments?
has the antigen-binding domain (variable region) and part of the constant H and L chains
how many Fc fragments are there?
1
what does Fc stand for?
Fragment crystallizable
what parts of the antibody are in the Fc fragment?
constant regions of the heavy chain
which fragment is recognized by receptors that bind antibodies?
Fc fragment
what type of bond holds antibody together?
disulfide covalent bonds
what type of 3D structures are antibodies folded into?
Beta sheets
what does CDR stand for?
Complementarity Determining Region
what is CDR?
Antibody-antigen binding site –> direct contact with Ag
what is the structure of CDR?
3 hypervariable loops per variable domain and are not part of the B strands
which part of antibodies have the greatest variability in the antibody sequence? why?
complementarity determining region to allow binding to diff antigens
where is CDR located on the antibody?
at the extremities of the antibody –> i.e. extremities are responsible for antibody:antigen binding
what type of binding occurs between the Ig and epitope? and 4 examples
NON-COVALENT BINDING
- H bonds
- van der Waals
- Hydrophobic
- Ionic
what is a way to describe specificity of the antibody:antigen binding?
lock and key
what are 2 types of variability that affect antibody:antigen binding?
- variability in size of epitope
- variability in antibody –> CDR varies in length
where are epitopes located on an antigen?
epitopes can be anywhere on an antigen –> antigen has many epitopes
what are the 5 classes of antibody?
- IgM
- IgD
- IgG
- IgE
- IgA
what is the main difference btwn classes of antibody?
different # of Ig-like domains in the constant region of the heavy chain based on diff AA sequence
is IgM a monomer?
no, it is a pentamer
describe the structure of IgM pentamer
5 IgM antibodies linked together via disulfide bonds
describe the heavy chain of IgM
1 variable region, 4 constant regions
describe how IgM is expressed on mature B cells vs plasma cells
mature B cells express transmembrane IgM (monomer) prior to activation
then B cell becomes plasma cell and forms pentamer
IgM is part of which wave of secreted antibodies?
IgM is part of the first wave
describe the heavy chain of IgD
1 variable region, 3 constant regions
IgD is part of which wave of secreted antibodies?
IgD is part of the first wave
describe the heavy chain of IgG
1 variable region, 3 constant regions
IgG is the most abundant in ______
IgG is the most abundant in plasma fluid
how many IgG subclasses are there? what is the difference btwn them
4 –> each with slightly diff functions
when is IgG produced?
after differentiation in the germinal center –> not 1st wave
describe the heavy chain of IgE
1 variable region, 4 constant regions
when is IgE produced?
to help Th2 get rid of Helminth infections
describe the heavy chain of IgA
1 variable region, 3 constant regions
describe the structure of IgA in plasma
monomer
describe the structure of IgA in mucous secretions in GIT and respiratory system
dimer
how does IgA become a dimer?
linking via J chain
IgA is important for which type of immunity?
mucosal immunity
how many subclasses of IgA are there?
2
why can antibodies be used as a drug? and an example?
antibodies can bind to any epitope –> ex. antibody against TNFalpha for rheumatoid arthritis
how are antibodies used in research?
ELISA assay or WB where an antibody conjugated with fluorescence can bind the Fc region of another antibody
why can an antibody therapy cause an immune response?
if the antibody is less similar to humans, your immune system can mount an immune response against it
