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58 Cards in this Set

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What are the phases in a humoral immune reaction?
1. Recognition
2. Activation
3. Effector
4. Decline/homeostasis
5. Memory
What types of microbes stimulate antibody production?
ONLY extracellular
What are the responding lymphocytes to an extracellular microbe stimulation of humoral immunity?
Bcells
What are the effector mechanisms of Bcells?
Antibody production
What are the functions of the Antibodies?
-Blocking infections
-Elimination of extracellular microbes
How does recognition occur in an initial, primary immune response? Where does it occur?
Microbe binds to a naive, IgM+ IgD+ Bcell, crosslinking at least two antibodies. Occurs in follicles in lymph nodes.
What happens when microbe binds a naive Bcell?
It activates the Bcell
Is Microbial binding the only thing that activates Bcells?
No, Thelper cells and other stimuli also activate naieve Bcells.
What does an activated Bcell do?
-Clonally expands
-Differentiates
What are 4 types of cells that Bcell clones can differentiate into?
1. Ab-secreting effector cells that secrete IgM
2. Ab-secreting cells that secrete IgG or other classes
3. High-affinity Ig-expressing Bcells via affinity maturation
4. Memory Bcells
When Thelper cells help stimulate Bcells, where does the interaction occur?
Near the paracortex at the marginal zone around a primary follicle.
What important function is mediated by humoral immunity and antibody production that is not conferred by other mechanisms?
PREVENTION of infection by viruses, bacteria and parasites.
In what forms are each of the antibody isotypes found?
Monomers: IgG, IgD, IgE
Dimer: IgA
Pentamer: IgM
When antigens initially stimulate Ab secretion in the peripheral lymphoid organs, where does the Ab go?
Into the bloodstream to be
1. delivered to the infection site
2. to mucosal secretions to prevent microbe entrance
When Ab's use the Fc region to activate effector mechanisms to eliminate microbes/toxins, what are 3 things they depend on?
1. Fab region recognition of the particular pathogen/toxin
2. Phagocyte and Complement participation
3. At LEAST 2 Ig molecules crosslinking the antigen
When is protection against a specific antigen conferred during a humoral response?
-During the first week of the primary infection
-Immediately upon 2ndary infection
What are the 4 categories of antibody effector functions?
1. Microbe/toxin neutralization
2. Opsonization/phagocytosis
3. ADCC
4. Complement activation
How do you remember the effector functions?
Christine Noac
-Neutralize
-Opsonize
-ADCC
-Complement
When Bcells differentiate into plasma + memory cells, which secrete Antibody?
-Plasma cells
How do memory cells function?
By retaining their capacity to secrete Ab and doing so upon 2ndary exposure to the antigen.
What does vaccination achieve?
The differentiation of memory cells, which will confer immediate antibody secretion and protection upon a real exposure.
What is the general goal of Isotype switching and Affinity maturation?
To enhance the protective functions of antibodies.
How is affinity maturation triggered?
By prolonged/repeated antigen stimulation
How is affinity maturation achieved for a vaccination?
By giving booster shots
Which antibody isotype has the most effector functions?
IgG
What are the 6 effector functions of IgG?
1. Neutralization
2. Opsonization
3. ADCC via NK cells
4. Complement activation (classical pathway)
5. Neonate immunity
6. Feedback Bcell inhibition
What is the main function of IgM?
Activation of the classical pathway of complement
What is the main function of IgA?
Mucosal immunity
Where is IgA secreted?
Into the mucosal secretions of the GI and respiratory tracts
What are the 2 main functions of IgE?
-ADCC via eosinophils
-Mast cell degranulation
What type of hypersensitivity is IgE involved in?
Type I - immediate
How do antibodies act to neutralize microbes and toxins?
By binding to them and preventing them from entering infected cells, or from infecting neighboring cells once infected cells die and lyse.
What is Opsonization?
The coating of a microbe or toxin with a substance that promotes phagocytosis
What is an Opsonin?
The substance that promotes phagocytosis
How do antibodies act as opsonins?
By binding to microbes which leaves their Fc regions free to bind to Fc receptors on macrophages and phagocytes.
When an Fc receptor of an Ab/Ag complex binds to a phagocyte, what is the response?
1. Phagocytosis of the complex
2. Activation of the killing mechanisms within the phagocyte
Where in the body is the major site of phagocytosis of opsonized bacteria?
The spleen
So what are splenectomized patients susceptible to?
Disseminated infections
Against what type of pathogen is opsonization the major host defense mechanism?
Encapsulated bacteria
Are all Fc receptors on phagocytes the same?
NO; they are different based on which isotype the Fc region is on.
Can free/naked antibody cause opsonization?
No; why would you want phagocytes to eat free antibody? It has to be crosslinked by microbe or toxin.
What is the major bacterial phagocytosis Fc receptor?
Fc-gamma-R1
What cells express Fc-gamma-R1?
-Macrophages
-Neutrophils
-Eosinophils
What antibodies bind best to Fc-gamma-R1?
-IgG1
-IgG3
-IgG monomer
What is the function of the Fc-gamma-R2B receptor?
It is the receptor that binds IgG-antigen complexes to turn down the immune response - negative feedback inhibition of Bcells.
What cells express Fc-gamma-R3A?
NK cells
What is the function of the Fc-gamma-R3A receptor on NK cells?
ADCC
What cells express Fc-epsilon-R1?
-Mast cells
-Basophils
-Eosinophils
What is the function of the Fc-epsilon-R1 receptor?
Cell activation and degranulation
ADCC is:
-antibody
-dependent
-cellular
-cytotoxicity
What cells do the killing in ADCC?
-NK cells
-Eosinophils
What is the Fc receptor on NK cells that allows for ADCC?
Fc-y-R3A
What is the Fc receptor on eosinophils that allows for ADCC?
Fc-e-R1
How is ADCC via NK cells stimulated?
By the coating of a microbe with IgG, and binding of that IgG's Fc region to the FcyR3A receptor on the NK cell.
What happens when NK cells are stimulated?
They release their cytolytic granule contents.
What are the cytolytic granule contents of NK cells?
-Granzyme
-Perforin
When IgE coats parasites in helminthetic infections, to what cells do the IgE's Fc regions bind?
Eosinophils
What cytokine is produced by Th2 cells that stimulates eosinophil proliferation and activation?
IL-5