Antigens and Antibodies

What is the composition of the heavy chain?

1 variable (V) domain/regions; Composed of 3-4 glocubular constanct (C) domains/regions C domain globular part is apart of the immunoglobulin sperfamily

What are the 5 classes of immunoglobulin (heavy chain)?

1. Mu (IgM), 2. Alpha (IgA), 3. Gamma (IgG), 4. Delta (IgD) 5. Epsilon (IgE) (names in reference to the heavy chain classes)

Where can antibodies be found?

1. floating in the tissues, circulation, and mucosal sites 2. On the surface of B lymphocytes

What happens to the Ig as the immune reactions process (2 things)? What does it result in?

1. somatic hypermutation 2. class switching TOgether it results in creating tighter binding of antibodies with different biologic functions

What are the 3 circumstances when antibodies are secreted from B lymphocytes?

1. stimulated by the relevant antigen 2. get "help" from T cells (from CD4+ effector T cells) 3. Differentiate into plasma cells

What is the structure of IgA?

2 forms monomer (mostly) and dimer.

How many heavy chains and light chains does an immunoglobulin (Ig) have?

2 heavy and 2 light chains

What happens as an immune response proceeds?

2 things: 1.Somatic hypermutation 2. Class switching

Which lymphocyte (B or T) can recognize antigens as they exist in nature and why?

B lymphocytes can because their epitopes are conformational whereas T lymphocytes epitopes are linear.

Which cells/immune response uses antibodies?

B lymphocytes or the HUMORAL response

When IgM declines, IgG and IgA are made from IgM: A. Directly B. Indirectly (through an intermediate) C. A and B D. none of the above

C. A and B

What chromosome codes for the heavy chain of the Ig?

Chromosome 14

What chromosome codes for the lambda light chain of the Ig?

Chromosome 2

What chromosome codes for the kappa light chain region of the Ig?

Chromosome 22

What is the function of IgE?

Defense against helminthic (worms) parasites, immediate hypersensitivity (ALLERGIC REACTION) Can bind to surface of Mast cells (sensitive to mast cells)

How do B cells know what isotype to change to?

Depending on the cytokines present - can go from IgM to IgG, IgA, or IgE

True or False: All antigens are capable of generating an immune response, therefore all antigens are immunogens.

FALSE, not all antigens are capable of creating an immune response, therefore not all antigens are immunogens

What does Fab (ab in subscript, not FAB for fabulous) do?

Fab is the ANTIGEN BINDING PORTION of the Ig.

True or false: All classes of immunoglobulins are made from different genes.

False. All classes of immunoglobulins are made from the SAME gene.

What is the function of Fc?

Fc = crystallizable The business end of the Ig, the biologic function part. This part binds to macrophages, neutrophils, and attaches to the complement. Does what the antibody is meant to do!

What is the significance of hte 4 fold increase in antibody titer?

If there is a 4 fold increase after the sx subside, it is indicative of having a primary infection.

How are Ig selected to proliferate from IgM?

Ig are selected for those mutations in the variable regions that actually result in tighter antibody binding. The better the activation signal, therefore the get a better activation. Why immune response get better

What is the second Ig that is most abundant in the plasma?

IgA (in monomer form)

What Ig is in breast milk?

IgA - will confer to the neonate

Which Ig(s) is almost always cell associated on the surface of b lymphocytes?

IgD

Which If(s) are sensitive to mast cells?

IgE

Which Ig provides rapid ejection of pathogens from the body?

IgE

Which Ig(s) can activate the complement system?

IgE and IgG

Which Ig are present in mucosal surfaces?

IgE and dimeric IgA

Which Ig class is associated preferentially with Memory?

IgG

Which Ig(s) are sensitive for killing by NK cells?

IgG

Which Ig(s) is involved in opsonization?

IgG

Which is the most abundant Ig present in the plasma?

IgG

Which Ig is involved in passive, natural immunity?

IgG => the only one that passes the placenta to the fetus!

Which are the major Ig involved in neutralization? (name the minor Ig)

IgG and IgA IgM is minor at it.

Which Ig(s) can diffuse into extravascular sites?

IgG and the monomer of IgA

Which Ig are present in the blood?

IgG, IgM, and monomer IgA

What is the first antibody that is secreted in an immune response?

IgM

What is the first class of Ig made in the classical complement cascade?

IgM - it has 10 binding sites, ergo good at binding hte complement

What Ig(s) does IgA function with in order to protect the tissues?

IgM and IgG

What is the significance of IgM and IgG?

IgM indicates a primary infection IgG can't tell if an infection is latent or primary (or whether from memory or not). Just can tell there is an infection.

How does IgE bind to pathogens, and which ones?

It binds via FcR (FcRe1) on: mast cells (connective tissue) basophils (blood) eosinophils (mucosal tissue)

What is somatic hypermutation?

It is a mutation that happens at a high frequency in the rearranged variable region DNA of the immunoglobulin genes in activated B cells. This results in producing variant antibodies, some that have a higher affinity for the antigen. Changes in the V region, allows better interaction. T cells help with in B cells.

What is the secretory component?

It is a remnant of poly-Ig receptor that binds with mucins.

What is FnRn?

It is an endothelial receptor that allows IgG to move into the tissue

What exactly is an antibody?

It is an immunoglobulin secreted in RESPONSE to antigenic stimulation

How is the titer expressed?

It is expressed as the reciprocal of the last dilution where the effect is seen. Ex: 1:256 => titer = 256

What is the V domain/region on an Ig responsible for?

It is responsible for antigen binding

What is ELISA?

It is the test using wells to measure if a patient's serum has particular antibodies. Used to measure antibody titer. Semiquanitative measure of amount of antibody present for a specific antigen.

What is an epitope?

It is the the ANTIGENIC DETERMINANT. The part of an antigen that directly interacts with the antigen receptor on lymphocytes

What exactly is an immunoglobulin (structurally/chemically)?

It is the variable, ANTIGEN-SPECIFIC glycoproteins made by B cells. Major compoenent of the blood and lymph.

What happens when IgG complex gets big enough?

It will precipitate with a soluble antigen. Sometimes called in vivo.

What are the 2 classes of immunoglobulin (light chain)?

Kappa and lambda

What do the epitopes for T lymphocytes look like?

Linear

What do the epitopes for B lymphocytes look like?

Linear and conformational.

What does Fc protein bind to?

Macrophages, neutrophils, and attaches to the complement. From the biological standpoint, does what the antibody is meant to do

What is the function of IgA?

Mucosal immunity Involved in neutralization ONLY Ig that can transport across the epithelium when in DIMER form MONOMER FORM can diffuse into extravascular sites

What is the function of IgM?

Naive B cell antigen receptor & complement activation

What is the function of IgD?

Naive B cell antigen receptor. It is always cell associated, existing solely on the surface of b lymphocytes and is not usually secreted.

HOw do we test for HIV? HOw do we know we have a false positive

Need to have 2 postivie ELISA test and a positive Western blot. IF the 2 Elisa are positive and a negative western blot, then we know we got a false positive for HIV.

Which Ig(s) can cross the placenta?

Only IgG

What is the function of IgG?

Opsonization, Complement activation, Antibody-dependent cell-mediated cytotoxicity, Neonatal immunity, Feedback inhibition of B cells Diffuses into extravascular sites

What Ig can be used to test for syphilis and mononucleosis (EBV)?

Particulate antigens agglutinate with IgG

What does pepsin do to Ig?

Protease enzyme cleaves Ig into 1 Fab and 1 Fc fragments below the hinge

What does papin do to Ig?

Protease enzyme that cleaves Ig into 2 Fab and 1 Fc fragment above the hinge

Which cells requires that the antigens be processed and be presented by the major histocompatibility complex (MHC)?

T cells

Where do antibody isotypes and subtypes differ in?

The C regions, thus influencing what they bind to and its effector functions

What do the mucins do in the mucosal epithelia?

The mucins in the mucosal epithelia keeps the IgA bound microbes from attaching to the epithelia.

What is the hinge region of an Ig?

The part of the Ig that links the Fab and Fc regions. Allows for flexibility to bind to antigens since antigens are not uniformly space in nature. "Molecular ball and socket joint"

What is the difference between the acute and convalescent titer?

acute titer is taken while the illness is symptomatic. convalescent titer is taken after symptoms subside

What is an immunogen?

any agent capable of inducing an immune response, why not all antigens are immunogens.

What is an antigen?

any molecule capable of binding specifically to an ANTIGEN RECEPTOR on B or T lymphocyte. Antigens generate or are recognized by antibodies.

What is class switching?

changes in the C region of the heavy chain, thus allowing changes in the isotype/ class type of the Ig.

What is the composition of the light chain?

composed of 1 variable (V) and 1 constant (C) domain/region

What form is IgA in mucosal surfaces?

dimeric

What makes up the V region?

hypervariable regions (interacting region) and less variable framework regions (framework region)

IF titer stays the same when repeated in a later time when sx subside, what does that mean?

it is a convalescent titer

What is the structure of a IgM?

polymerized pentamer with 10 binding sites (therefore 10 epitopes can be cleared by 1 IgM)

What can antigens be made of?

protein, carbohydrates, lipids, an nucleic acids. Antigens are usually a protein for T cells; antigens that are carbs, lipids, or nucleic acids are particularly recognized by B cells.

Which Ig(s) can cross the epithelial barrier?

the dimer form of IgA

How does dimeric IgA move out of the mucosal surface?

there is Poly-Ig receptor on the basolateral side of the epithelial cell that binds specifically to the J chain of IgA and IgM. It is then secreted on the luminal side with a remnant of poly-Ig receptor (this is called the secretory component)

How many fold is the serum diluted in ELISA?

usually 2 fold increments until the antibody is no longer detectable

What form is IgA in the blood?

usually monomeric in blood

How does the "violent" expulsion of pathogens occur?

when the receptors cross-link, this will lead to the release of mediators that will act on the smooth muscle.

What is the structure of IgG?

- exists as a monomer - 2 affinity binding sites per molecule - the FcRn (an endothelial receptor) allows the IgG to move into tissue

True of False: All immunogens are antigens but not all antigens are immunogens.

True

What are the 3 different encoded sections of the heavy chain "V"region?

V: variable D: diversity J: joining

What are the different encoded sections of the light chain "V" region?

V: variable J: joining NO D

What is a plasma cell?

When a B lymphocyte is exposed to an antigen, it differentiates into plasma cells to secrete antibodies.

What does the Western blot test for?

a way to tell (esp in HIV suspected cases) if the antibodies that are specific for a particular protein are present