Chapter 11 Antibodies (Abs) or Immunoglobulins (Igs) Flashcards
Antibodies are ______
glycoproteins produced by plasma cells In response to antigens.
what kind of globulins are Antibodies?
gamma globulins
all Igs consist of four polypeptide chains made up of what?
two identical Light chains and two identical heavy chains held together by a noncovalent and covalent inter and intrachain disulfide bonds. Each chain consist of a variable region and a constant region.
Do IgM and IgE have a hinge region?
They do not have a hinge region.
What is the hinge region?
the proline-rich region between the CH1 and CH2 domains. confers segmental flexibility on the Ig molecule.
What does Papain do?
Cleaves IgG above the S-S bond at the hinge region, producing two antigen binding fragments and one crystalizable fragment.
What does Pepsin do?
Cleaves IgG below the S-S bond at the hinge region, hence the hinge region and interchain disulfide bonds are retained in an F(ab’)2 molecule but the Fc fragment is degraded.
Fab and F(ab)2 can bind to antigens without activating what?
Fc-dependent effector functions.
What does the Fc piece of the antibody do?
Activates complement, can bind to Fc receptors on various cells, initiates placental transfer.
What does the lg identical light chains consist of?
200-250 amino acids linked by S-S bonds to a heavy chain.
What are the two type of isotype classes of light chains?
Kappa and Lambda, A given Ig molecule always contains two Kappa or two lambda light chains but NEVER a mixture of both.
Each Ig molecule consist of 2 identical heavy chains: each heavy chain consist of ?
each heavy chain consists of 450-600 amino acids.
Different CH isotypes and associated Fc regions perform distinct effector functions, such as?
eg, complement activation, opsonization
What do the 3 hypervariable regions of a light chain and the 3 hypervariable regions of a heavy chain form?
they form the antigen-binding site.
What must happen to bring about neutralization and/or elimination of an antigen?
an antibody must bind tightly to the antigen.
this interaction is characterized by noncovalent, reversible binding.
What does Affinity mean?
how strongly an antibody is attracted to an antigen
What is Avidity?
the sum total of the strength of binding of two molecules such as antibody and antigen.
What is an isotype?
refers to the amino acid differences in the CL and CH regions that distinguish each immunoglobulin class and subclass.
What is an Allotype?
Characterized by a few amino acid differences of Ig CL and CH regions
What are allotypic differences used to establish?
Paternity and determine blood stain origins.
What is an idiotype?
these are generated by unique combination of amino acids in the variable regions of the light and heavy chains. Each idiotype is unique for the antigen specific antibody produced by a clone of B cells.
What is the primary function of an antibody molecule?
to bind antigen
When are effector functions of antibodies initiated?
when antibodies bind to their specific antigens and engage other effector molecules ( comp. proteins)
Who mediates most of the effector functions of immunoglobulins?
mediated by the Fc portion of the heavy chain.
What mediates Ig neutralization ?
mediated exclusively by Fab binding of antigen and does not require participation of Ch regions. ( sorry this was a shitty question its the last part on page 111, look at it your self if your bitching) =o)
When IgG binds to Dog poo and cat shit what antibody is produced!?!
HAHAHA you were like what????? but this is how i feel about IMMUNO…..WHO THE FUCK CARES>….. NOBODY!
Does the Fab region have effector functions?
No
What are the effector functions of the Fc region?
bind with macrophages and neutralization- covering bacteria with antibody
What are Fc receptors?
Cell surface receptors that bind the Fc portion of an antibody molecule. they help mediate effector functions.
What immunoglobulin is the major one in serum?
IgG
It is found in blood, tissue spaces and extravascular spaces.
What does FcyRIIB express and where is it found?
It is found on B cells and expresses an inhibition motif, when cross linked to the BCR, it delivers inhibitory signals to the B cell blocking B-cell activation.
What are the functions of IgG?
1.)opsonization 2.)Neutralization 3.)only antibody that can cross the placenta in some species.
What is the first Ig produced?
IgM first Ig class produced both during the development of B cells and during the primary immune response.
What is the most efficient Ig in agglutinating matter?
IgM
complement activation
What are some functions of IgM?
- most efficient in agglutination
- monomeric IgM- antigen receptor BCR on naïve B-cells.
- Neutralization of viruses and toxins
- Opsonization- IgM is not an opsonin bc phagocytes don’t posess FcuRs, but it is a potent complement activator.
- Predominant Ig produced by the fetus
Is IgM and opsonin?
No but it is a potent complement activator
what would an elevated IgM level in the blood of a newborn be indicative of?
transplacental infection
where does synthesis of IgA occur?
mainly in mucosal lymphoid tissues esp GI and Resp tract
what are the IgA forms?
two forms
- Secretory IgA (sIgA) in various body secretions, present as a dimer plus a joining chain and a secretory component.
- serum IgA is present mostly as a monomer
What Ig is predominant in various secretions?
Secretory IgA ( in saliva, tears, milk etc.)
What are some functions of IgA?
- in secretions: milk, tears, saliva
- protects mucosal surfaces by preventing attachement
- Agglutination of antigens
- Serum IgA is in low concentration so its a minor component of humoral immunity
How many CH domains does IgE possess?
4
IgEs Fc portion binds to what?
FceRs on mast cells, basophils and eosinophils
JUST KNOW THIS!!! IgE is Heat labile at 56 C
IgE is Heat labile at 56
What are some functions of IgE?
- mediates immediate hypersensitivity (anaphalxis) by causing release of mediator such as histamine from mast cells. this is why its known as a reaginic antibody
- Defense against some helminth infestations
What is the only known function of IgD?
as a antigen receptor on naïve B cells. Its heat lable at 56C
What is ADCC?
the killing of antibody coated target cells by nonspecific cells with Fc receptors that recognize the Fc region of the bound Ab
who mediates most ADCC?
Natural Killer cells that have FcyRIII(CD16) on their surface
what type of Fc does Macrophages and neutrophils express?
FcyRs and kill target cells via IgG mediated ADCC
What type of Fc do Eosiniphils express?
FceRs and kill helminth parasites via IgE mediated ADCC
what are monoclonal antibodies?
they are antibodies that arise from a single clone of cells are homogenous and are directed against only one epitope, such antibodies are called monoclonal antibodies (mAbs)
what does polyethylene glycol cause?
cell fusion
What does Hypoxanthine aminopterin-thymidine HAT cause?
kills the ones that don’t fuse
