Chapter 5 Antibodies Flashcards
What is the hinge region of an antibody? Purpose?
It is a flexible region that lets the antibody open and close so that it can fit and bind the antigenic determinant.
What does Fc stand for? Where is it on the antibody? What is it made of?
Fragment crystallizable. It is the base/constant portion of the antibody. Made of heavy chains
What are the parts of an antibody? Start from bottom up
-Fc region made of constant heavy chain
-hinge region
-Light (outer) and heavy (inner) chain constant regions
-Light (outer) and heavy (inner) chain variable regions at the tips. Directly bind antigen
How many Ig classes are there? List them
5
1. IgG
2. IgA
3. IgM
4. IgE
5. IgD
Immunoglobulins (Ig) are what portion of the blood?
Gamma globulin portion of the blood
Antibody polypeptide chains are linked by what type of chemical bond?
Disulfide bonds
What does the constant region bind?
Host
What determines antibody class?
Constant region of stem
Describe IgM antibody
-Pentamer with 10 binding sites (not BCR) circulates in blood plasma
-Monomeric form is BCR
-Does not show up Day 0 of infection, but is the first to show up in infection (military power) (first Ab secreted by plasma cells)
-blood clumper because of many binding sites
-Readily fixes and activates complement
Describe IgA antibody
-Present in breast milk, sweat, saliva, and tears
-Dimer
-Prevents germs from attaching to epithelial cells/prevents entry of pathogens
-known as secretory IgA
-Monomer exists in limited amounts in plasma
Describe IgD
Very common B cell receptor
Describe IgG
-Monomer that exists as 75-85% of plasma antibodies
-Form secondary and late primary responses (indicates that you HAD an infection in the past)
-Gestational, crosses placenta
-Released in greater concentrations than IgM
-Neutralize (bind) antigens so that they can’t do anything
-Complement fixation
-Enhances phagocytosis
Describe IgE
-Monomer involved in parasitic infections and allergies
-Causes mast cells and basophils to release histamine by binding stem end to them, then antigen binding to Fab end triggers histamine release
-Traces found in plasma
-Secreted by plasma cells in skin, mucosa of GI tract, respiratory tracts, and tonsils
What is class switching? Example?
When B cells switch antibody classes but retain same antigen specificity. For example, antibodies will switch from IgM to IgG (plasma cells switch secretion type)
What is the simplest defense mechanism? Describe it
Neutralization. It’s when antibodies block sites on viruses or bacterial exotoxins. This prevents antigens from binding receptors on tissue cells. Then the Ag-Ab complex gets phagocytosed
Describe agglutination
It’s when one Ig binds multiple RBCs and cross-links. Enhances phagocytosis
Which cellular immune reactions involve cross-linking?
Agglutination and precipitation
Describe complement fixation and activation
-It’s the main antibody defense against cellular antigens (bacteria, mismatched RBCs)
Steps:
1. Neutralization
2. Complement pore structure binds Fc of Ig, water gets into pore, cell lyses
What happens upon complement activation?
-Amplified inflammatory response
-Phagocytosis via opsonization
-Positive feedback to recruit more immune cells
Types of antigens involved in agglutination and precipitation?
Agglutination = cell-bound
Precipitation = soluble free floating
How are MoAbs produced? Describe them
Hybridomas = fusion of tumor cell + B cell. Can proliferate forever and make one type of Ab
Can Ab get inside cell?
Yes, if attached to virus prior to entry, then activate destructive mechanisms
Describe multiple myeloma
Type of bone cancer caused by single plasma cell that has become neoplastic (new type of cell). Production of abnormal, homogenous Ig called myeloma proteins (M-proteins) that can be detected by electrophoresis. Plasma cells clump in various sites
What is M-protein also called?
Paraprotein
What is the myeloma-causing plasma cell clumping in one region called?
Solitary plasmacytoma
What is serum?
Plasma minus clotting factors
Multiple myeloma effects on regular cells?
Pancytopenia. Neoplastic plasma cells crows out normal components of bone marrow.
Low RBC = shortness of breath, fatigue
Low platelet = bleeding, easy bruising
Low WBC = increased susceptibility to infections
Effects of multiple myeloma on bone
Osteolysis, which leads to the release of calcium ions because they comprise bone structure (hypercalcemia)
Multiple myeloma effect on blood?
Higher viscosity (hyper viscosity syndrome)
Immunoglobulins are what type of globulin?
Gamma
What is the light chain of M-protein Ig called? Where is this protein found and why?
Bence Jones proteins are found in urine and can cause damage of renal tubular cells bc of Ab deposit buildup, which leads to GLOMERULONEPHRITIS
Describe glomerulonephritis
It’s when Ab deposit buildup happens on glomerulus (filtering unit made of capillaries in kidney) such that inflammation occurs
What is the glomerulus?
Filtering unit made of capillaries, found in kidneys
Papain splits Ab into how many components? What are they? Which fragments retain biological activity?
3
Fab, Fab, Fc
Fab retain biological activity BUT cannot precipitate Ag
Pepsin breaks Ab into how many fragments? What are they?
-More than 4 fragments
-F(ab)^2 bivalent and 4 Fc sub fragments
Mercaptoethanol breaks Ab into how many fragments? What are they?
4
2 heavy chains of 55 kDa
2 light chains of 22 kDa
All species have which two types of light chains. Name them.
Kappa and lambda
Can a person produce both kappa and lambda light chains? What about Ig?
Person, yes
Ig, no
What are the 5 heavy chain classes and their correspondence with Ig class?
IgG = gamma
IgA = alpha
IgM = mu
IgE = epsilon
IgD = delta
What is the most important trait of heavy chains?
They confer different bio functions on each Ig class (e.g., half-life, activate enzymes when bound to Ag)
Where is the hinge region found on Ab? Which Ig have longer hinge regions? Made of which aa?
Between CH1 and Ch2 of heavy chains.
IgD and IgE have longer hinge regions
Lots of Cys and Pro (Pro prevent globular folding)
Function of hinge region?
Flexibility to open and close to bind epitopes
Allow enzyme access for cleaving
What is the hyper variable region? Describe?
Also known as complementarity-determining region, which determines antigen specificity. There are 3: CDR1, CDR2, and CDR3 separated by variable but less variable FLEXIBLE REGIONS
How many CDRs are on each Ab? How are they distributed?
12 total. Each of 2 variable heavy chains has 3, so 6. Then, each of 2 variable light chains has 3, so 6 more. In total, 12.
Can two Ab with different specificities/aa sequences bind the same epitope?
Yes, but with different binding affinities
What is redundancy in Ab?
When Ab can combine with 2+ epitopes
Define isotype, allotype, and idiotype
Isotype = different Ig class (IgM, IgE…etc)
Allotype = same Ig class, bind same Ag, but different alleles
Idiotype = same Ig class/isotype, but different VH or VL arrangement such that they bind different Ag bc one is an idiot
Where do you find IgG and what does it look like? MW?
-2H and 2 L chains (either kappa or lambda) held together by disulfide bonds
-Majority Ig in blood, lymph fluid, and CSF
-MW 150 kDa
-Equally distributed inside and outside blood vessels
-15% of protein in serum
How many IgG subtypes are there and which are they?
IgG1 (most abundant)
IgG2
IgG3
IgG4
All have different biological properties
What are the biological properties of IgG?
-Half life about 23 days (except IgG3 with 7 day half-life)
Can cause agglutination of Ag, leading to precipitation of Ag for easy phagocytosis
How is IgG recycled?
- Binds to Ag
- IgG protection receptor protein binds Fc portion and protects it during endocytosis from lysosomal degradation
- IgG is cleansed (dissociated) of its Ag and released out of the cell
What is FcRp?
Fc receptor protector
Name how pH affects FcRp
Acidic pH = binds Fc region of Ab
Neutral pH = dissociates Fc region of Ab
Which Ig passes through the placenta? Describe
-IgG (except IgG2)
-3rd/4th month of pregnancy, rapid increase in [maternal IgG] in fetus
-3-4 months after birth baby starts to make own IgG
-baby has IgG protection receptor in intestine to absorb IgG from mother’s milk/colostrum
Which cells express Fc receptors? What do they bind?
-Phagocytes (macrophages, neutrophils, dendritic cells)
-bind antibody-coated bacteria
-Fc receptors adhering to IgG Fc makes zipper-like closure
What does IgG activate? What does this lead to?
Complement system (made of more than 30 serum proteins). Leads to lysis
What type of junk to IgG neutralize?
-toxins, flagella of bacteria, viruses
What is scorpion venom useful for? Describe
It has potassium channel blocking peptides, so suppresses KCNA3 channel to control T cell proliferation
Structural features of IgM?
-First Ig produced after immunization
-900,000 Da macroglobulin
-Pentamer held together by J chain (holds monomers together)
-J protein made by B plasma cell. J protein is component of IgM and IgA, 15 kDa
IgM and IgA require _____ and ___ to be secreted into mucosa
Which 2 Ab polymerize?
IgM and IgA
Do IgA and IgM need J chain to polymerize?
No
Biological properties of IgM? Found where?
-Bind only 5 Ag, not 10
-Found intravascular spaces, and on B cells with IgD
-Don’t pass through the placenta but is made by fetus during 5th month
-bridge Ag too distance for IgG
-Can bind Ag with repetitive epitopes such as polysaccharides on bacteria
What does increased [IgM] in fetus indicate?
Congenital or perinatal infection (3 months before to 1 month after birth)
What are isohemagglutinins?
Natural Ab that recognize ABO blood groups
Which Ab binds ABO blood group antigens?
IgM
IgM activates what?
Complement.
How many IgG and IgM are needed to activate complement
IgG = at least 2
IgM = 1 bc many binding sites
IgG and IgM concentrations during primary and secondary responses
IgM = same
IgG = higher in secondary response
IgM shortfalls?
-Half life of 5 days
-Not versatile, so not good at neutralizing toxins or binding to viruses
Structure of IgA?
-Dimer held by J-chain
-alpha H chain that is larger than gamma H chain IgG
-low serum concentration: IgA = 1.8 mg/ml and IgG = 12 mg/ml
-MW 400,000 Da
-6 day half-life
-IgA1 (93%) and IgA2 (7%) subclasses
Biological properties of IgA?
-Found in secretions, saliva, mucus, sweat, gastric fluid, and tears
-Present in lamina propria below basement membrane of epithelia (respiratory, GI, urinary tracts)
-Major Ig of colostrum and milk
-prevent viruses from entering host
-works with lysozyme to be antibacterial to G-negative organisms
-prevent Vibrio from attaching to GI tract and causing cholera
Describe transcytosis
-When dimeric IgA binds Poly-Ig receptor and gets moved from outside to inner lumen of vessel
Structural features of IgD?
-Delta H chain larger than gamma H or alpha H gains in IgG and IgA
-low serum concentrations bc never leaves B cell membrane
-expressed as a BCR, often co-expressed with IgM
-MW 180 kDa
-no subclasses defined
Function of IgD?
Eliminate B cells from becoming auto reactive??? WE don’t exactly know
Structure of IgE?
-epsilon H chain larger than gamma, alpha, or delta H chains
-MW 200 kDa
Bio properties of IgE
-lowest serum concentrations of all Ig
-shortest half life of 2 days
-0.00002 mg/ml (2X 10^05)
-binds Fc-epsilon receptors on basophils and mast cells and may be retained (sensitized) for weeks/months
What are in basophil and mast cell granules?
Histamine, heparin, leukotrienes
How does Fc-epsilon binding work for IgE?
-Fc portion binds Fc-receptor on mast cell or basophil
-allergen binds IgE, which causes cell to release granules
How long until Ab detection after immunization? Why is this time lapse needed?
12 days. Needed to give time to activate T and B cells
How long is response after second injection?
3-6 days. Ab production will continue for long time (months or years)
What is affinity maturation?
Ab made binds better to Ag, so select for best B cells that bind Ag
List proliferation cytokines
IL-2, IL-4, IL-5
Which are the differentiation cytokines?
IL-2, IL-4, IL-5, IFN-gamma, TGF-gamma
Molecules associated with Ig super family?
-Ig
-Ig alpha/beta heterodimer
-T cell receptor with alpha and beta portions
-CD3
-MHC I and II
-Poly Ig-receptor
