Exam 7: Chapter 9 Flashcards
What is the role of C1r?
To cleave both itself, the other C1r, and both C1s molecules
What is the ultimate goal of B cell activation?
To differentiate the B cell into a plasma cell
Why is transcytosis an important process for infants?
- Allows IgA in mother’s milk to be taken up by the gut of the infant
- Allows IgG to be taken up through the placenta and delivered into the fetal blood stream
What receptor do mast cells have that allow them to tightly bind IgE?
FceR1
What part of the B cell activates FOS?
B-cell receptor
What signal is required for class switching to occur?
The CD40-CD40L signal
How do antibodies function?
Antibodies target pathogens for killing by non-specific aspects of the immune system
What are zymogens?
Inactive, ciruclating forms of the complement enzymes
What is the role of CD19?
Signaling component
What are the four movements that can be observed in the IgG molecule?
Waving, Rotating, Wagging, and Bending
What is the role of CD81?
Localize co-receptor complex
What two signals are needed for a B cell to be activated?
- Binding of specific antigen by the BCR
2. B cell co-receptor signals
What are TI-2 antigens?
Repetitive carbohydrate antigens that extensively crosslink the BCR so second signals are not required
What is the role of CR2?
Receptor for complement
What do germinal center B cells do during late infection?
Become memory B cells
What happens to B cells that do not move into the medullary cords?
They form a germinal center and start to proliferate to form centroblasts
How is Syk activated?
Lyn phosphorylates Syk, allowing it to bind to phosphorylated ITAMs
Which form of IgA does the poly-Ig receptor bind?
The IgA dimer
What interaction between B and T cells must occur in order for B cells to undergo affinity maturation, class switch, and memory B cell formation?
B cells must bind specific antigen, internalize it, process it, and present Class II MHC peptides to CD4+ T cells
What happens if activated B cells move directly into the medullary cords?
They differentiate into plasma cells that only express IgM and have not undergone somatic hypermutation or affinity maturation
What are TI-1 antigens?
Antigens that activate other receptors in addition to the BCR
Why do T-independent antigens not require T cell help?
These antigens are repetitive and made up of polysaccharides, lipopolysaccharides, and peptidoglycans
In what cells does somatic hypermutation occur?
Centroblasts
What is the main problem with TI-2 antigens?
They elicit only an IgM response and are often responded to by B1 B cells, which cannot produce memory B cells
What do germinal center B cells do during early infection?
Migrate to other sites and become plasma cells
What are immune complexes?
Antibody-antigen complexes that form when antibodies bind soluble self-antigens
What part of the B cell activates JUN?
CD19
What is the role of C1s?
To cleave C4 into C4b and C4a and to cleave C2 into C2b and C2a
What antigens are T-dependent?
Protein antigens
How do bacterial toxins aid in infection?
They block the immune response by killing immune cells, inducing vascular permeability, and affecting cells in the gut
What cells make up the “dark zone” of a germinal center?
Proliferating centroblasts
What happens if immune complexes are not cleared from circulation?
They can aggregate in the kidney and impair function
What receptor transports IgG into the tissues?
FcRB
How is the classical complement pathway activated?
By an antibody binding to a pathogen
What molecule is secreted by T cells and helps induce B cell proliferation?
IL-4
Where does affinity maturation occur?
In the germinal center
What are the two mechanisms by which antibodies identify pathogens?
- Fc region of the antibody interacts with specific cells
2. Antibodies activate the complement system
How many binding sites does IgM have for the C1 complex?
5
What signals for mast cells to release granules?
The cross-linkage of two IgE molecules by an antigen
How do NK cells function in the innate immune response?
Fc receptors on NK cells recognize antibody coated target cells, leading to the release of cytolytic vesicles and antibody-dependent cell mediated cytotoxicity
What cells make up the “light zone” of a germinal cetner?
Non-dividing centrocytes
What three things are triggered by Fc-Fc receptor interactions?
- Uptake of the antigen followed by its destruction in the phagolysosome
- Release of nitric oxide and ROS
- Release of hydrolytic and microbicidal peptides
Where are activated B cells kept within the lymph node?
In the T cell area, where they can interact with helper T cells
How do antibodies target pathogens?
Antibodies neutralize toxins and viruses and opsonize other pathogens
Which two antibody isotypes are especially good at fixing complement?
IgM and IgG3
What complement fragment does CR2 bind to?
C3d
How are centrocytes selected for?
Centrocytes must bind and process antigen and interact with a TH2 cell in order to receive the survival signal
What are iccosomes?
Bundles of pieces of membrane coated with immune complexes
Why must C1 bind multiple adjacent IgG molecules?
Because IgG molecules have only one binding site for C1
What antigens are T-independent?
Non-protein antigens
What facilitates activation of the B cell co-receptor?
Phosphorylation of CD19 by Lyn kinase
Which B cell components contain ITAM motifs?
The IgAlpha and IgBeta proteins
What portion of an antibody do Fc receptors bind to?
The constant region
What two chains make up a toxin?
One chain that binds a cellular receptor and a second chain that has the toxic activity
What proteins make up the B cell co-receptor?
CR2, CD19, and CD81
What is the role of C1q?
To bind to the Fc portion of the antibody
How are immune complexes cleared from circulation?
CR1 on erythrocytes bind immune complexes and transport them to the spleen and liver to be cleared by phagocytes
How is a pathogen (or toxin) destroyed once identified by an antibody?
Specific receptors on phagocytes recognize the Fc portion of the antibody and stimulate internalization of the antibody-antigen complex
