Lecture 8 Flashcards
What is the antigen binding site of an antibody made from?
the VH and VL domains
What is found within the VH and VL domains?
there are hypervariable regions (light and heavy chain)
- What are the hypervariable regions made up of?
- why is this important for antibody-antigen binding?
- o the amino acids found in these regions vary significantly from one antibody to another of the same isotype.
- The amino acids of the hypervariable region are the region that binds to the antigen
- How many hypervariable regions in an antibody molecule?
- Are they next to each other in a linear structure?
- 4-5 hypervariable regions
- not next to each other in linear structure
How is the antigen binding site generally formed if the hypervariable regions are not next to eachother?
When the protein is folded the hypervariable regions come together to form the antigen binding site.
Is there only one antigen binding site shape?
- vary in size and shape, for example they may have the shape of a:
- Groove
- Extended surface
Describe the antigen binding site of an Ig molecule, the structure and function
- Antigens bind to specific amino acids in the variable regions of the heavy and light chains.
- They typically bind in a region known as the hypervariable region of the antibody, which is where there is variability in the variable region of the amino acid sequence.
- The areas that have the highest variability are in the beta pleated sheets, and they all fold onto the ends of the region.
- This happens on both the heavy and light chains.
- The antigen actually only binds to very specific amino acids
Define antibody affinity
The affinity of the bond between antigen and antibody is the sum of the non-covalent forces
o Ionic
o Hydrogen
o Hydrophobic
o Van der Waals
regarding antibody affinity
- Which affinity would have the best fit?
best fits have higher affinity- more bound than unbound antibodies
What is affinity maturation
the progressive increase of affinity of antibody for an antigen as the immune response occurs; increases over time
The antibody in a primary response has lower or higher affinity than antibody in subsequent responses.
lower
low affinity antibodies will have more or less cross reactions?
more
What is a linear epitope?
Antibody binds to parts of the antigen that are adjacent to each other
T cells recognize linear or discontinuous epitopes on MHC molecules?
linear
What is a Discontinuous or conformational epitope
Parts of the antigen are brought together by folding (they are not adjacent linearly)
What happens if you denature the antigen and destroy its conformation if the antibody recognizes it by a conformational epitope?
antibody cannot bind (does not recognize the antigen)
3D structure of antigen is important for antibody to bind, not important for T cells because?
because antibody can bind to conformational epitopes, but T cells only bind linear epitopes
regarding a discontineous or conformational epitope
- If antibody is made to epitopes of a denatured protein and then the animal is exposed to the natural protein will the antibody recognize the natural protein antigen?
the antibody may not recognize the antigen because the natural conformation conceals the epitope the antibody would detect
What is the first antibody to respond?
IgM
Which antibody is the largest?
IgM
regarding IgM
- What is it secreted from?
- What is its shape?
- What is it held together by?
- How many epitopes?
- Secreted from plasma cells
- pentamer
- held together by J chains
- can bind 10 epitopes
regarding IgM
- What is it very good at and why?
- Does it leave the bloodstream or stay in it?
- good or bad at agglutinating bacteria?
- Because it is a pentamer it has many Fc regions and is very good at fixing compliment (it takes two Fc regions very close together to fix compliment)
- Stays mostly in the blood stream because it is too big to get out.
- Very good at agglutinating bacteria (because of a valence of ten)
regarding IgM
- does it have a short or long time in serum
- what is its half life in serum
- what % of total antibody in the serum is it
- short
- half-life 5 days
- 6%
regarding IgG
- how many heavy chain domains does it have
- where is it found in the body
- does it cross the placenta?
- 4 heavy chain domains
- Found in the blood stream and in the interstitial fluid in tissues
- Crosses the placenta in humans and in some other species, e.g. rodents, a little in dogs and cats.
regarding IgG
- It is found in high concentrations in colostrum in what species?
- half life in serum?
- % of total antibody in serum?
- large domestic species, e.g. horses, cattle, pigs
- half-life 23 days (3 weeks)
- 80%
What are 6 functions of IgG
- Complement activation
- Agglutination
- Neutralization - of toxins and viruses, for example
- Opsonization
- Systemic (absorbed into the bloodstream) immunity in newborn (either via placental transfer or from colostrum, depending on the species)
- Antibody dependent cell mediated cytotoxicity (ADCC)
regarding secretory IgA
- how many heavy chain domains does it have
- held together by?
- when is the secretory component added?
- 4 heavy chain domains
- Held together by J chain
- Secretory component is added to the molecule as it is transported to the mucosal surface and has important functions to allow IgA to work on mucosal surfaces and not be degraded
regarding IgA
- where is it mostly found?
- in what state is it found in the blood?
- half life?
- % in serum?
- IgA is produced in higher quantity than any other immunoglobulin in the body (not the blood); most of it is found on mucosal surfaces
- In the blood it is usually a monomer (dimers are transported to mucosal surfaces),
- half-life of 6 days
- makes up about 13 % of total serum antibody
What are 2 important functions of IgA?
- It is important for mucosal immunity and is found on mucosal surfaces where it can neutralize toxins and block entry of pathogens
- It is also found in mother’s milk and helps provide intestinal immunity to neonate
regarding IgE
- how many domains in heavy chain?
- what is attached to the heavy chains?
- Five domains in heavy chain
- A lot of polysaccharide attached to heavy chain
- Fc portion of IgE has high affinity for
for the Fc receptor on mast cell (Fc εpsilon receptors)
- Binding of antigen to the IgE on a mast cell can result in
- IgE can also activate
- Binding of antigen to the IgE on a mast cell can result in mast cell degranulation
- IgE can also activate eosinophils (they have lower affinity Fcε receptors)
regarding IgE
- where is it mostly found?
- half life in serum?
- % in serum?
- Most IgE is found on mast cells and the concentration in plasma is low = homocytotrophic (cell loving); binds to Fcε receptor before it binds antigen (different than the other types of antibodies)
- Half-life in serum about 2.5 days
- 0.002 % of total serum antibody
2 functions of IgE
- Important in defense against helminthic parasites
- Mediator of immediate hypersensitivity (allergy).
- where is IgD found?
- what is it important for?
- Mainly on B cells as a B cell receptor.
- It is important in B cell development; a marker of maturation.
3 ways antibody can function in protection from disease that result from binding and interference – antigen binding site is responsible
- Agglutination – clumping the pathogens together
- Neutralize toxins – bind to toxin so it cannot bind to its receptor
- Block attachment –block virus or bacteria from binding to cell receptor
- Antibody to HA antigen on influenza blocks the virus from infecting cells
- Antibody to pili of E. coli prevent binding in the G.I. tract
3 ways antibody can function in protection from disease that result because of the – Fc portion; Ab acts as a flag
- Complement fixation – through the classical pathway; the binding site for C1 is on the Fc portion of IgM and IgG
- Opsonization for phagocytosis by neutrophils or macrophages; the Fc receptors (FcR) on neutrophils and macrophages bind to the antibody bound to antigen
- Antibody-dependent-cell-mediated cytotoxicity (ADCC); antibody binds to antigen on a cell surface and a cell with killing mechanisms, e.g. (neutrophil, macrophage, natural killer cell,) recognizes the “flag” (Fc) and binds via an FcR and kills the cell the antibody is bound to
Draw a graph explaining the primary and secondary response to an antigen. Be sure to label:
- X and Y axis (approx. time vs. Ab concentration)
- Primary response
- Secondary response
- IgM
- IgG
Define immune complex
- An immune complex is formed from the integral binding of an antibody to a soluble antigen.
- The bound antigen acting as a specific epitope, bound to an antibody is referred to as a singular immune complex.
Define multiple myeloma, include the type of cell that becomes neoplastic
Multiple myeloma is a tumor of plasma cells
Briefly explain why bones are involved in multiple myeloma
- A differentiated B cell (plasma cell) is transformed into a neoplastic cell
- The neoplastic cells metastasize widely but have a predilection for bone
- These neoplastic plasma cells secrete immunoglobulins; since the neoplastic plasma cells are from one clone they all secrete the same immunoglobulin (monoclonal).
- Multiple myeloma may secrete IgG, IgA, rarely IgM or just the light chains
Draw a normal serum electrophoresis pattern and identify where antibodies/immunoglobulins are found
Draw a serum electrophoresis pattern that would be indicative of multiple myeloma
Explain the basic difference between a polyclonal gammopathy and a monoclonal gammopathy
- A monoclonal gammopathy (antibodies are gammaglobulins) determined by serum electrophoresis is indicative of multiple myeloma.
- Since the tumor cells are overproducing all the same antibody molecule they cause one tight peak on the electrophoresis print out. In chronic infection, when many different clones of plasma cells are making antibody, the peak is wide because the molecules vary in the electrical charge.)
