Antibody Structure 2 & Response Flashcards
What are the two types of light chains? What are the functional regions of these chains?
Kappa or lambda
Functional regions: 2 domains. 1) Variable 2) Constant
What are the two types of disulfide bonds in an Ig? Which is more constant?
Interchain and intrachain. Intrachain is almost always the same.
What are the classes of heavy chain for each Ig class?
A - alpha D - delta G - gamma E - epsilon M - mu
What are the four domains of an IgG heavy chain?
One variable domain and the N terminus, then 3 constant domains
One constant + variable = Fab
2 constant = Fc
What is the purpose of the hinge region?
Between constant domains 1 and 2 of heavy chain, allows for flexibility of Ig binding.
Where do carbohydrates attach to Ig’s?
To the second constant domain of the heavy chain, which is the first part of Fc
What is Fv?
The smallest fragment which retains site for Ag reaction. The two variable domains of heavy and light chain
What does Papain vs Pepsin fragmentation do? Why is this significant?
Papain - Breaks at hinge, leaving 2 Fab and 1 Fc
Pepsin - breaks in the Fc region, losing Fc function (how Fc function was determined)
What are the Fc functions?
Complement fixation
Cell binding
Transplacental passage (IgG functionality)
What is the only multimeric Ig?
IgA, as it normally exists in two forms in the serum
Monomeric (7S, like IgG)
Polymeric - normal and secretory form
Heavy chain has alpha1 and alpha 2 subclasses
What is the purpose of the J chain for IgM and IgA?
Joining chain - holds together than individual Ig monomers to make the larger structure (pentamer and dimer respectively)
Which Ig was the first to evolve, and what are its functions? How many domains does its heavy chain have?
IgM, involved in agglutination and serum primary response.
Has a 5th domain (4th constant region) for attachment to J chain to make pentamer
What is IgD structure and where does it exist?
It is a monomer which has a partial 5th domain (slightly larger than IgG) - mostly exists on cell surfaces, especially developing or anergic B cells
What is the structure of IgE and how many domains does it have?
monomer, stays attached to mast cell surfaces most of the time but can be free. Involved in immediate hypersensitivity
Has one extra domain (4th constant) for attachment to cell
Do the dimensions of the antigen binding site vary for different antibodies?
Yes
Where do contact residues exist? About what percent do they make up?
In the Variable regions of the heavy and light chains
Make up about 6% of the Ig
What are CDRs / Hvs and how were they determined? What is between them?
CDR = complementarity determining region
Hv = hypervariable region
same thing
Determined via sequence analyses of antibodies made from myeloma patients producing all the same B cells and hence Ig class
In between them: framework regions
What is isotypic antibody diversity?
Differences of antibodies between classes and subclasses (i.e. IgM vs IgG and IgG gamma1 vs IgG gamma2)
What is allotypic antibody diversity? What region does it affect the most?
The genetically determined amino acid insertions different between individuals, mostly in the constant region. Will cause differences within a subclass.
What is idiotypic antibody diversity?
Diversity of the variable regions, could be due to changes in CDR or framework
How can you vaccinate someone without ever having them see the antigen in question? Why might this be done?
Expose a rat to the antigen, it will make antibody 1.
Give antibody 1 to another rat, it will make anti-antibody1, which is the same as antigen.
Give anti-antibody1 as vaccine, which is sometimes safer than giving the original antigen
What are some of the features of the antigen which can influence immune response?
degree of foreignness - more = better
chemical features
if it is particulate, higher reaction than soluble
presence of adjuvant
Which ellicits a better immune response, immunization or real infection?
LOL r u kidding tho
How do subcutaneous / GI immune challenges result in circulating Abs vs a bloodborne challenge?
Subcutaneous / GI must move through lymphatic system first (subcut through lymph nodes, but Peyer’s patches directly via thoracic duct) through the thoracic duct to the internal jugular vein.
Bloodborne challenges have antigens in the spleen which releases antibodies directly into circulation from the B cells in the white pulp.
How do lymphocytes from the blood enter the lymph nodes?
Through addressins on high endothelial venules, which allows them to slow via selectins and then attach via integrins / ICAMs. They diapedisify through the HEV into the lymph node.
What class of Ig are most serum antibodies, and where are they synthesized?
Most are IgG, synthesized by plasma cells in the spleen and lymph nodes
Where do the antibodies of mucosal surfaces get produced?
In the plasma cells of the glandular tissue / lamina propria of mucosal surfaces
What would be an internal vs external mucosal secretion, and what are the predominant antibody classes?
Internal - IgG - aqueous humor, CSF, synovial or pleural fluid
External - IgA - saliva, lacrimal fluid, tracheobronchial fluid, bile, intestinal fluid, vaginal secretions
How does secreted IgA differ from systemic IgA?
Systemic - can be monomer, dimer, or trimer, and only has J chain
Secreted - always a dimer with J chain and secretory component (remaining part of poly Ig receptor)
What is the primary vs secondary antibody response?
Primary - low affinity Ab, IgM, with low titer and longer lag time. IgG turns on only late
Secondary - high affinity Ab, short lag time with large IgG response, higher titer, although IgM could still appear early
What is the secondary antibody response called?
Anamnestic or recall response
What are the relative half lives of all the Ig’s?
IgG > IgA > IgM > IgD > IgE
GAMDE, like a mispelling of GAMED. Just remember E is the shortest because of the allergy response
Where is the mucosal immune response the highest? What Ig classes is synthesized in the highest amount?
The GI system, which produces more antibodies than the spleen
IgA accounts for 60% of the total Ig produced
What are the three functions of secretory IgA?
- Barrier defense
- Antigen transport
- Intracellular viral neutralization
What is an example of the adaptive mucosal immune system function?
Ag presents in a Peyer’s patch with Microfold cells present. B cells travel after Ag exposure to the mesenteric nodes then thoracic duct, into the bloodstream.
B cells then migrate into various mucosal glands and tracts, where they begin secreting IgA which is uptaken by corresponding epithelial cells and released as sIgA.
What are examples of mucosal glands / tracts which secrete sIgA?
Mammary gland, salivary glands, bronchial tract, UG tract, lacrimal gland
How are the heavy and light chains synthesized in plasma cells?
On separate ribosomes, via separate mRNA transcripts, leader sequences included. There are different pathways for assembly for different Ig classes
What is the order of disulfide bone formation?
Intra first, then inter
Where in the cell are the carbohydrates added to the second conserved domain of the heavy chain?
Golgi complex
How are Ig’s secreted?
Reverse pinocytosis (exocytosis)
Where are the J chain and SC (secretory component) synthesized?
J chain = also in plasma cell. J chain catalyzes polymerization shortly before secretion
SC = epithelial cell
What does the poly Ig receptor interact with on the IgA?
Both the J chain and the alpha heavy chain domain
When is it called the poly Ig vs the SC?
Only called SC after the membrane insert piece splits off from the epithelial cell.
When can you have a plasma cell which produces IgM for the purpose of making sIgM?
Whenever there is an IgA-deficient patient
