Unit 4 - Humoral Immunity Flashcards
What do lymphatic vessels contain?
Carry lymphatic fluid instead of blood (likes veins and arteries)
True or False:
Organs are tightly packed with leukocytes
True
What is the (believed) role of tonsils?
Entrap pathogens, rich in leukocytes
What is the role of the spleen? Will you find leukocytes there?
Filters blood
- rich in leukocytes!
How is the humoral system different than the cell-mediated system?
Humoral immune components are dissolved in extracellular fluid
Identify which of the following is cell-mediated or humoral (neutrophil, complement, antibodies, cytotoxic t-cells)
Humoral = complement + antibodies Cell-mediated = neutrophil + cytotoxic t-cells
What are clonal cells?
Cells that are GENETICALLY identical
True or False:
Bacterial cells are clones
True
What is the name of the process that occurs that makes some lymphocytes no longer genetically identical?
VDJ recombination
What is the name of the process that occurs after VDJ recombination?
Class switching
True or False:
Every cell recognizes only a single, unique epitope
True
What recognizes the epitopes of antigens?
Receptors of lymphocytes
Are antibodies made when an antigen is contacted?
No
- B-cells already have antibodies present on their outside prior to an infection
- They DO undergo clonal expansion when the specific B-cells contacted their specific antigen
What is an antibody?
A secreted B-cell receptor
What are the components of the antibody?
- Antigen binding site
- Light chain (small polypeptide)
- Heavy chain (large polypeptide)
- light chain and heavy chain are bound by sulfide bond
What is special about the antigen binding site?
Specifically shaped to bind to a specific epitope
Define affinity
The strength with which an antibody (or other receptor) binds its epitope
Why is the antigen binding site regarded as hypervariable?
The shape varies from one antibody to another
What is the variable (V) segment of the antibody?
The antigen binding site (at the tips, “hands”)
What is the constant segment of the antibody?
The area the specifies the antibody function
- made up of the light and heavy chains
What is the fragment of antigen binding site (Fab)?
Made up of:
- The antigen binding site
- The light chain
- The top piece of the heavy chain
What is the fragment crystallizable (Fc) segment of the antibody?
It connects it to the B-cell
- made up of the bottom half of the heavy chain
How can antibodies by split at their hinge region?
By some proteases
- ex: papain protease
During a primary infection, is the antibody response fast or slow?
Slow
What 3 things happen to B-cell during an infection?
- Clonal expansion
- Class switching
- Memory cells form
What is another name for the primary infection?
Sensitization
Why does a secondary immune response happen faster?
Memory B-cells promote a faster antibody response
True or False:
Naive B-cells are in greater number than memory B-cells
False
- Memory B-cells are in greater number than naive B-cells
True or False:
Antibodies switch from IgM to a more effective class, IgG
True
True or False:
Plasma cells still have their antibodies
False
True or False:
Memory B-cells still have their antibodies
True
True or False:
Every antibody starts off as an IgG
False
- every antibody starts off as an IgM
During a primary response, what is the class of antibody from plasma cells that is first created?
IgM
True or False:
There is a latent period in the secondary infection
False
- no latent period b/c memory cells from the primary infection still exist
- they mount an immediate response
What is the difference between the primary and secondary infections?
First = latent period; first IgM and then IgG (peaks at separate times) titer tapers back to low levels Second = no latent period; IgG response is MUCH stronger and faster compared to primary infection; antibody levels are sustained for several weeks
What is another name for plasma B-cells?
Effector cells
What segment of the antibody give rise to distinct antibody classes?
Fc
= fragment crystallizable
What is the function of IgM?
Primary immune response
- B-cell receptor
What is the function of IgD?
Undefined
- B-cell receptor
What is the function of IgA? Where is it found?
Prevents adhesion
- found in breastmilk and mucosal surfaces
What is the function of IgG?
Long-lasting immune response
What is the function of IgE?
Allergic response
- also protects against parasites
What kind of antibody class will we have, if the antibody class DOESN’T change?
IgM
How does B-cell class switching occur?
- Genes in HEAVY chain of an IgM expressing B-cell
- Removal of DNA segment by enzyme activity
- Non-homologous end joining of DNA at switch regions
- Genes in HEAVY chain will become whichever class gene is expressed FIRST after the VDJ segment
The following is a transcript of an IgM:
VDJ … M, G, A, E, D, M
And the portion, MGA is deleted. What class will this antibody become?
Class E = IgE
VDJ … E, D, M will be leftover
True or False:
Once a B-cell has switched classes, it cannot switch back
True
- If a B-cell switches from a IgM to a IgG, it cannot switch back
How are IgM structed when they are on the B-cell, and how are they structured when they are expressed/secreted?
On B-cell = monomeric
Secreted = pentameric
True or False:
IgM has the ability to fix complement
True!
- Complement will bind to IgM
When an IgM goes from monomeric to pentameric, what is the joining factor?
A “J” chain
What antibody is secreted as part of the primary response?
IgM
What two functions of antibodies (there are 4 in total) goes IgM participate in?
- Agglutination
2. Complement fixation
If IgM forms a pentomer once it is secreted (sIgM), how many binding sites will it have?
10!
What kind of antibody is used in blood typing? Why?
IgM
- because the precipitate will form and “fall out” of the solution
What does the complement system promote?
Chemotaxis, inflammation, opsonization, and formation of membrane attack complex
True or False:
IgM antibodies induce chemotaxis
False!
- they activate (or are bound to) the complement system, which DOES have chemotactic factors
True or False:
IgM antibodies do not participate in the lysing of cells
True
- IgM antibodies activate (or are bound to) the complement system, which forms the MAC (membrane attack complex)
What do we need to know about IgD?
That it exists!
- the function of IgD is unclear, might be similar to IgM
What does IgA form when it is secreted?
Dimer
- two IgA molecule will join together by a “J” chain
What virulence factor does IgA prevent?
Adherence!
Where is IgA predominantly found?
Seromucosal secretions
- saliva, colostrum, breastmilk, tracheobronchial and genitourinary secretions
What is the greek letter that is associated with IgM?
µ = IgM
What is the greek letter that is associated with IgA?
α = IgA
What is the greek letter that is associated with IgE?
ε = IgE
What is the greek letter that is associated with IgG?
γ = IgG
What is the greek letter that is associated with IgD?
δ = IgD
Why are IgA antibodies not destroyed by stomach acid (like the antibodies found in breast milk)?
Part of the Fc-A receptor remains BOUND to the sIgA dimer as a “secretory component”
- makes sIgA resistant even to stomach acid
What segment of the IgA antibody is involved in neutralization?
Fab
- the VDJ section and the light chain, and the top portion of the heavy chain
Explain how IgA neutralizes toxins
IgA prevents binding to the surface of the cell by binding to the epitope on the antigen (toxin)
What binds to GP120 and prevents it from contacting with the HIV receptor CD4?
mAB B12
Which antibody is involved in the secondary immune response?
IgG
What antibody makes up 80% of circulating immunoglobulins?
IgG
True or False:
IgG’s are able to cross the placenta and give passive immunity to the fetus
True
What functions (of antibodies) are IgG’s able to do?
All 4 of them!
- Neutralization
- Opsonization
- Complement Activation
- Agglutinate
How does IgG participate in opsonization?
Directly = phagocytes are more effective in capturing extracellular antigens when they are coated with antibodies such as IgG
What kind of receptors are on the phagocytes that bind to IgG?
Fc-gamma receptors
Mom passes IgG to baby in utero, but what are the first three antibodies that the baby makes on it’s own?
- IgM
- IgG
- IgA
Under what two conditions are IgE levels elevated?
- Type 1 hypersensitivity
2. Parasitic infections
What is a Type 1 hypersensitivity?
Allergic response to re-exposure to antigen
- mast cells and basophils release histamine)
True or False:
Mast cells could have IgEs deposited on them
True
- and if they are stimulated, they will cause the cell to degranulate and release histamine
True or False: Either mast cells or eosinophils could be bound to the FC-E receptor
True
What is the most common antibody?
IgG
What is the least common antibody?
IgE
- because they are already stuck to mast cells
Where is the FC-gamma receptor located?
On the phagocyte
- IgG is an opsinin
Where are Fc-alpha receptors located?
On epithelial cells, supports secretion
Where are Fc-epsilon receptors located?
On basophils or mast cells
- stimulates degranulation
True or False:
Fc segment of antibody determines the antibody role
True
Review what the roles/function are of the major 5 types of antibodies.
IgM = primary response IgG = major antibody of secondary response sIgA = secretory component, seromucosal secretions IgE = allergy, parasite
If an APC (antigen presenting cell) presents an antigen to a T-helper cell, what could the response be?
- Humoral (antibodies)
2. Cell-mediated (cytotoxic t-cells)
How do macrophages activate T-helper cells (TH-0 cells)?
With IL-1
What happens to TH-0 cells if they ONLY secrete IL-2?
Cell-mediated response
- TH-1 cells
- CYTOTOXIC T-CELLS
What happens to TH-0 cells if they secrete IL-2 and IL-4?
Humoral response
- TH-2 cells
- Activate B-cells
What are the steps of helper T-cell activation in the humoral response (and B-cell activation)?
- Dendritic cells eats and presents an antigen
- Dendritic cell secretes IL-1 (stimulates helper T-cell)
- B-cell would have eaten same antigen and presented it to helper T-cell
- Helper T-cell secretes IL-2 and IL-4, changes it to TH-2 cell
- TH-2 cell activates B-cell
- Activated B-cell antibodies undergo class switching (IgM to IgG)
- Plasma B-cells and Memory B-cells are formed
Are the vast majority of antibodies produced from T-cell dependent or independent cells?
T-cell dependent
If you remove the thymus and an HIV infection prevents the formation of mature T-helper cells, can T-cells still be made?
Yes!
- T-cell independent ones can still be made
Define serology
Branch of immunology involving testing serum
What do you typically test for in serum?
- antibodies
- antigens
- cytokines
In an agglutination / precipitation test, if the antigen is NOT bound to a microbe, what will happen to it?
It will precipitate
What was the agglutination/precipitation test for, that was developed over 100 years ago?
Typhoid fever
= “Widal Test”
- caused by salmonella typhi
How do we make polyclonal antibodies?
- Inject animals with antigen
- Collect blood and isolate the serum
- Purify the IgG
What are the pros and cons of polyclonal antibodies?
Pros = cheap; able to produce large amounts; against ALL the epitopes of the protein Cons = there could be cross-reactivity (serum sickness)
How do we make monoclonal antibodies?
- Remove spleen from immunized mice
- Fuse spleen cells with myeloma cancer cells
- Select a single cell (one cell = one epitope)
- it is LESS likely to react with your own cells than compared to polyclonal
What is immunostaining?
Binding stain or fluorescent molecule to an antibody
- then cells bearing the antigen will glow!
What is the antigen highly expressed in some breast cancer cells that we are able to stain for?
Epidermal growth factor (her2)
= anti-her2 antibody conjugated to stain, allows us to visualize breast cancer cells under the microscope
What does flow cytometry measure?
The AMOUNT of antigen per cell
- ability to count a large number of cells
What kind of test is used to count the amount of CD4+ cells in HIV/AIDS?
Flow Cytometry (FACS)
- counts AMOUNT of antigen per cell
- < 200 cell/ml = HIV/AIDS
What does ELISA stand for?
Enzyme-linked immunosorbent assay
What does ELISA measure?
Amount of antibody present
- an enzyme is conjugated to antibodies
- when antibody is present, the enzyme causes a color change
What is a classic example of an ELISA test?
An allergy test
- antigen in serum
- add in patient’s serum + enzyme
- if it changes color, there is an allergy present
In direct ELISA, what is added first - the antibody or the antigen?
Antibodies
What is the order of the three things added to a direct ELISA?
- Antibodies - wash off excess
- Add patient serum with suspected antigen (antigen will bind with antibodies present in test)
- Add 2nd antibody that is bound with an enzyme that will change color of solution if antigen is present
What is the order of the three things added to an indirect ELISA?
- Add antigen
- Add patient serum (if allergic, patient serum WILL have antibodies against antigen)
- Add 2nd antibody that is bound to an enzyme that will change color if it binds to the Fc segment of the first antibody
What does Immunoblotting test for?
The size of proteins and the specific antigen is detected by immunostaining
What is the purpose of an agglutination test?
Rapid test for serum antibody
What is the purpose of elecrophoresis?
Separation by size
What is the purpose of immunostaining?
Detection of antigen on cell surface
What is the purpose of flow cytometry?
Amount of antigens per cell
- number of antigen +ve cells
What is the purpose of ELISA?
Amount of antigen in a sample
What is the purpose of immunoblotting?
Visualizing a specific antigen
What is the home based pregnancy test based on?
ELISA
- enzyme-conjugate antibodies bind hCG
- induces color change
