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70 Cards in this Set

  • Front
  • Back
How are antibodies first expressed?
as Ag receptors on B cells
What cells secrete antibodies?
plasma cells which are differentiated B cells
Describe immunoglobulin gene rearrangements.
Millions of new B cells, with each one having a different Ag receptor on their surface, are generated in the bone marrow everyday.... process of creating unique Ag receptors is by immunoglobulin gene rearrangements
What type of receptor is on newly formed B cells?
What is the only thing that can keep a B cell from dying?
an encounter with an Ag
What are the two forms that immunoglobulin is found? Describe each.
secreted protein forms

The trans-membrane form confers Ag specificity onto the B cell

secreted antibody form is the effector molecule of the B cell part of the immune system
Where will you find most of the plasma cells?
Most of the plasma cells in the bone marrow. Another major reservoir of plasma cells is along the body's mucosal surfaces.
What do mucosal plasma cells secrete?
IgA to protect mucosal surfaces
What is the major protein in serum and what were the other protein peaks?
Major protein - albumin

other protein peaks - alpha, beta, and gamma-globulins
What is the antigen binding portion of serum?
gamma globulin... now it is called immunoglobulin
What is the molecular mass of gamma globulins?
Describe the 2 fragments that result as a result of digesting gamma globulins with Papain.
produced two identical fragments which they called Fab (Fragment Ag binding) and another fragment that was very homogenous and easily formed crystals called Fc(Fragment crystallizable)
Describe the basic structure of IgG.
2 identical heavy and 2 identical light chains
What is the N- terminal portion of the light chain?
variable region (V region)
What is the C portion of the light chain?
constant and is either a kappa or delta light chain isotype but was otherwise identical among the myeloma light chains
Describe the heavy chain.
variable at the N terminal and the rest of the protein was constant
Name 4 characteristics of immunoglobulins.
1. At least one end was probably involved in binding Ag (variable region)

2. Heavy chain defines the isotype (M, G, A, D, or E)

3. Each isotype will have either a K or lambda chain in both light chains

4. An individual antibody molecule with have 2 identical light and 2 identical heavy chains
What is the importance of complementary determining regions?
These regions are the variable regions on immunoglobins. They are on the both the light and heavy chains. They form the antigen binding site
What is the hinge region?
This region endows the Ab molecule with some flexibility. The region is proline rich and allows the arms of the Ig to be flexible and reach out and hold epitopes with bond arms. This region is more susceptible to proteolytic enzymes.
What is one signifcant fact about the variable region on the Ab?
The variable regions are identical on both ends of the arms of an Ig molecule
Which Ig contain hinge regions? Which do not?
Contain hinge: IgG, IgD, and IgA

No hinge: IgM or IgE
What is the most abdundant Ig in the serum?
IgG - 80% of total IgG
What is the function of each of the following Ig:

IgM - efficient activator of the complement system; only 1 IgM molecule is needed to activate complement

IgG - good at opsonizing Ab; it's important in fetal immunity becayse IgG can cress the placenta mediated by an Fc receptor that allows the fetus to have the same concentration in its blood as the mother

IgA - mucosal protection

IgE - allergy and asthma
What is Hyper IgM immunodeficiency?
patient can only make IgM and makes a lot of it

They cannot isotype switch. There are several versions. One is an X-linked form where the patients lack CD40 ligans, which is very important on T cells to help with switching

They don't have any mucosal antibodies, although sometime IgM can get across the mucosal like IgA.

IgM is big and has a hard time getting out of the vasculature and into the interstitial spaces
What happens when a patient is IgA deficient?
the patients are ok
Describe the structure of IgG?
2 gamma heavy chains and 2 K or lambda light chains
How many subclasses of IgG exist? How do they differ

The serum concentration corresponds to the number
IgG(1) - most abundant
IgG(4) - least abundant

The major difference is the length of the hinge region.

IgG(3) has a huge number of interchain disulfide bonds and extended hinge region, which probably accounts for the fact amoung the subclasses, IgG(3) has the shortest half life

There are AA differences in teh constant regions, which affects function -- some cross the placenta better or activate complement better
Describe the structure of IgM
a pentamer of IgM monomers

the pentamer is held together by a component called the J chain/Joining chain. It is involved in the polymerization of IgM. It is required for getting the correct # of monomers into the IgM molecule

Potentially, it has 10 Ag binding sites
What is the significance of IgM?
It is the first antibody that you produce during an immune response, because your original B cell have IgM on their surface
What is the concentration of IgM in the blood serum?
1 mg/ml
In what form does IgA exist in the serum? What is its concentration?
monomer and its concentration is about 1 mg/ml in blood serum
What is the major fxn of IgA?
protection of mucosal surfaes from mucosal derived pathogens
What is the major Ig produced everyday?
IgA - but because a lot of it gets dumped into the intestines it is not the major isotype
Where do many plasma producing IgA cells tend to migrate?
along the intestines and oral cavities
Describe the microenvironment of Peyer's patches?
Isotype switching occurs preferrentially to make IgA. B cells respond to antigen, get T cell help, and make IgA

They differentiate into plasma cells tend to migrate and sit in the lamina propria under the epithelial cells and secrete IgA
How does IgA get across the basement membrane?
The transport system involves the polymeric Ig Receptor

IgA is dimeric with a J chain. On the basolateral surface of the epithelial cell, there is the poly Ig receptor that bings the dimeric IgA. The J chain is important for binding to the Polymeric Ig Receptor. The receptor gets internalized and transports teh IgA to the surface of the epithelial cell.
What makes the Polymeric Ig Receptor?
epithelial cells in the mucosal surfaces
What is another fxn of the the polymeric Ig receptor (also known as the secretory component)?
to mask the proteolytically sensitive sites of the molecule so that it stabilizes the protein in the intestinal juices
Where will you find IgA(1) versus IgA(2)?
IgA(1) - beginning of the intestinal tract

2 - end of tract
Describe IgE.
Associated with allergies
Has very low serum level

Most of your IgE is actually sitting on the mast cells and basophils waiting to interact with antigen

Mediates type 1 hypersensitivity by Ab bound to basophils/mast cells on the Fc (e) receptors, which can bing IgE w/o antigen
How are mast cells and basophils activated?
Allergen comes along and is able to cross linke 2 of the receptors, there is transduction and release of histamine, other vasoactive amines, and cytokines that result in the symptoms of type 1 hypersensitive
Describe IgD.
mysterious Ab

When B cells are first formed, they IgM as a transmembrane Ag receptor, but then, they start to make IgD.
What CD is expressed on B cells?
If someone is immunized with protein antigens, what immunoglobin is seen in the secondary immune response?
What the reversible featerues of the antigen-antibody interaction?
These are non-covalent interactions.

1. electrostatic forces - positively and negatively charged AA

2. hydrogen bonds
3. van der Waals forces - intermolecular non-covalent forces

4. Hydrophobic forces - hyrophobic AA preferring to associate with each other whereas the hyrdophilic ones can associate with aqueous environment
What are the forces that are important for the Ab molecule to assume its proper 3-D structure?
electrostatic and hydrophobic forces
What forces are important for Ab-Ag interactions?
hydrogen bonds and van der Waals forces -- the weaker forces
Define affinity.
The strength of the binding between the antigen and the Ab

ease of association or dissociation
Define avidity.
The increase in affinity due to multivalent binding

Summation of multiple affinities
What is an Ag?
a substance that can be recognized by antibody or T cells.
What makes a good Ag?
complexity and phylogenetic difference
What does it mean to have a phylogenetic difference?
The immmune system has the capacity to make auto-antibodies, but most of the clones of the B cells that are autoreactive are eliminated. So the more similar it is to self the less likely it is to make an Ab.

Phylogenetic differences are those differences that allow it to differ from self
What type of molecules are more immunogenic:

large or small?
carbs, lipids, proteins?
subcutaneous versus oral?
proteins more so than carbs which is more so than lipids

subcutaneous but depends on the Ag
What are adjuvants? What are common adjuvants used?
Adjuvant - agents which are used to elicit both an innate and adaptive immune response against something that wouldn't normally elicit a response

Alum (aluminum hydroxide) is use because it makes a depot for Ag, so the Ag stick to the alum and doesn't dissipate into the surrounding tissues

Myobacterium tuberculosis - stimulates toll like receptors
Define immunogen.
Substance able to generate Ab or T cell responses
What is a hapten?
non-immunogenic susbtance, usually non-immunogenic because it's a small molecule weight compound
How can you make antibodies to haptens?
you can make antibodies to haptens if you chemically couple the hapten to a large protein, which is called a carrier

Once you make Abs to haptens, they can bind the antibodies so they become "antigens"
Name a drug that is a hapten.
Penicillin -- It can actually haptenate your self proteins. It chemically attaches itself to self proteins and you make antibodies to it -- only becomes a problem if its IgE antibodies
What is direct inhibition?
antibody blocks target and thereby inhibits the activity
What is agglutination?
Have bivalent antibodies and multivalent antigen... you can make big complexes if you have a polyclonal response and that complex can get so large that it can fall our of solution and precipitate

These immune complexes can be harmful in vivo.
What is the role of antibodies in phagocytosis?
Antibodies enhance phagocytosis. Bacterium get coated with antibodies and macrophages have Fc receptors that bind to the Fc region of the antibodies. Then you get internalization and destruction of that microorganism by the macrophage.

There are also complement receptors on some of the phagocytic cells. If your antibody activates complement, you get even better phagocytosis through complement and Fc receptors
What are the good things that Antigen-Antibody interactions produce?
1. Neutralization of viruses and toxins
2. Opsonization of pathogens
3. Complement lysis of bacteria
4. Prevention of bacterial adherence
What are the bad things that Antigen-Antibody interactions produce?
Transfusion reactions

What is hemiagglutination used for? Give an example.
used to identify blood group antigens or antibodies to them

If A antibodies are added and agglutination occurs -- meshwork will form instead of a pellet you will know that blood used is either A or AB
What is Enzyme Linked Immunsorbent Assay (ELISA)?
1. Coat wells in antigen
2. Add serum sample to see if any antibody to antigen in serum
3. If antibody present it will bind to Ag
4. Wash off an unbound Ab
5. Use secondary Ab to bind the first Ab -- secondary has enzyme conjugated to it
6. Add a colored substrate.

If have color change to tell if there are antibodies present to the original antigen
What is the first line assay for HIV infection?
ELISA, but they have a significant false positive rate. So, if you test positive, then you do a Western Blot
Describe the technique of the Western Blot.
Take HIV and dissociate it in SDS and use polyacrylamide gel electrophoresis to separate all the different HIV proteins

Transfer the HIV proteins from the gel to nitrocellulose membrane.

Incucbate the membrane with blood serum and see whether there are antibodies to the different HIV viral proteins
What is agglutination inhibition?
1. Take urine sample and add Ab to it and look for macroscopically visible clumping or agglutination of the beads

If there is HCG in urine, you are going to soak up Ab. When you add the beads, no Ab is free so the beads will not clump

However, if there is no HCG in urine and you Ab, none will bind. Then you add beads which will bind with the free Ab, causing clumping
Specifity depends on what regions of the immunoglobin?
variable regions of the immunoglobin heavy and light chains

After antibody binds to antigen, the outcome depends on the constant region of the heavy chain
Effector functions are determined by?
antibody isotype