B Cells & Antibodies Flashcards
What chromosome are the gene segments that make up the final heavy chain (Hc) gene located on?
Chromosome 14
What are the four separate gene segments that make up the finished heavy chain protein?
V, D, J, and C
What do we call the antigens that match the B-cell receptor (BCR)? What do we call the region of this antigen that binds BCR? How many AA’s is it usually?
Cognate
Epitope - 6 to 12 AAs
Which immune system decides whether an invasion is dangerous - innate or adaptive?
Innate
What is a B cell called if it has never encountered its cognate antigen? What if they have encountered their cognate?
Naive or virgin
Experience
What are the two ways naive B cells can be activated?
- W/ assistance of helper T cells (T-cell dependent activation)
- T-cell independent activation
What two signals does activation of naive B cells require?
- Clustering BCR’s w/ cross-linking + co-stimulatory signal
2. T-cell dependent activation signaling supplied by helper T cell
What is the surface protein on helper T cells that binds to B-cells and sends co-stimulatory signal to activate B cell?
CD40L
What is the only type of antigen Th cells recognize?
Protein antigens
What is the third, unusual/abnormal way BCRS can be activated?
Mitogen binds to molecules on B cell surfaces that are NOT BCRs and clusters them - this is polyclonal activation that does not depend on cognate Ag
What are the three steps of B cell maturation? Is this order-dependent?
- Class switching
- Somatic hypermutation
- Career decision
Not order dependent
What types of antibody does a virgin B cell produce when first activated?
IgM antibodies (the default)
also IgD, but only a small fraction
What region of the antibody determines its class?
Fc (constant) region
What Ab class is very good at activating complement cascade? How does it do this?
IgM - it binds C1 complexes formed by complement on its Fc region, bringing them close together, which forces inhibitors to fall off and initiates the cascade that produces C3 convertase
IgG also binds C1 to its Fc region, but only one copy (so you need a lot of IgG around)
What IgG subclass fixes complement the best? What types of cells have receptors for this subclass’s Fc region?
IgG3 - Natural killer cells
What IgG sublcass is good at opsonizing invaders for macrophage ingestion?
IgG1
What is another name for IgG antibodies?
Gamma globulins
What is the most abundant Ab class in the human body?
IgA - guards mucosal surfaces (digestive, respiratory, & reproductive)
(IgG is most abundant in the blood)
What Ab class is structured like two molecules held together with a clip?
IgA
What Ab class is structured like 5 IgG antibodies put together and is massive?
IgM
What Ab class is good at collecting pathogens into clumps large enough to be cleared with mucus and feces? Can it also fix complement?
IgA - cannot fix complement
What Ab class is secreted into milk of nursing mothers?
IgA
What Ab class can pass across placenta to fetus?
IgG
Degranulation of what cell causes anaphylactic shock?
Mast cells (tissue basophils)
What Ab class is produced in large amts in response to allergen exposure?
IgE
If an area is rich in cytokines IL-4 and 5, what class do Abs switch to?
IgE (good for parasites)
If an area is rich in IFN-alpha cytokines, what class do B cells produce?
IgG3 (good for bac. and viruses)
If an area is rich in TGF-beta cytokines, what class do B cells produce?
IgA (good for viruses)
What types of cells secrete cytokines that direct Ab class switching and somatic hypermutation?
T-helper cells
What region of the Ab does somatic hypermutation mutate?
Fab - Antigen binding region
What is T-cell independent B cell activation usually a response to? Does it undergo class switching? Somatic hypermutation?
Carbohydrates on bacterial surfaces
No class switching, no somatic hypermutation
Through what process does a B cell change its constant, Fc region? Its antigen binding region, Fab?
Fc - class switching
Fab - somatic hypermutation
What are the two fates of B cells?
Plasma cells - antibody factories
Memory cells
