L8: B cell-mediated immunity I Flashcards
What is the main function of B cells?
produce antibodies
What is somatic hypermutation?
allows B cell responses to increase in affinity as they develop
What is isotype switching and what benefit does it provide?
Allows B cell responses to be tailored to best deal with the particular pathogen
How can B cell responses be retained?
In the form of memory B cells, providing lon-lived immunity to re-infection
What is the first signal of activation for a B cell? The second?
First is recognition of its cognate determinant in an antigen by BCR.
Second is activation by TH1 or TH2 cell.
Where do B cells proliferate and differentiate?
In germinal centers
What is the signal transduction unit for the BCR?
the Ig-alpha and Ig-beta complex.
This requires cross-linking of multiple antigen-receptor complexes
What is complement receptor 2 (CR2)?
It is the B cell co-receptor. It binds to a breakdown product of C3b (C3d)
If a B cell is activated, but there are no activated effector T cells, what is the antigen likely? What else could it be?
the antigen is likely a self-molecule and this is a method of tolerance.
It could also be a non-protein determinant of a pathogen.
What is a T-independent antigen?
a non-protein antigen that can elicit B cell activation in the absence of T cell help
What are TI-1 antigens? How do they work?
TI-1 antigens have an intrinsic capacity for inducing B cell proliferation. They engage the BCR as well as the pattern-recognition receptors on B cells. AKA mitogens
What are TI-2 antigens? How do they work?
TI-2 antigens act by heavily crosslinking BCRs on the surface of the B cell.they are usually composed of cell wall polysaccharides.
What will high concentrations of mitogen do?
polyclonaly activate B cells. This only happens in lab experiments
What can low concentrations of TI-1 mitogens do?
elicit an antigen-specific IgM response
Can infants have a TI-2 antigen response?
no. It takes 1-5 months for B1 B cell populations to build up
Where are germinal centers established?
within lympoid follicles
What is happening in germinal centers?
somatic hypermutation results in B cells with higher or lower affinity for antigen.
Cytokines produced by helper T cells promote isotype switching
Positively selected high-affinity isotype-switched B cells differentiate into memory and plasma cells.
What does IL-5 promote class switching to?
Augments production to produce IgA
What does IL-4 do?
Induces change to IgE
Can plasma cells be induced to proliferate?
No, they are permanently differentiated.
Do plasma cells have Surface MHC class II?
No
Do plasma cells have surface Ig?
No
Do plasma cells have high-rate Ig secretion?
Yes. primary function is to secrete Abs.
Where is IgM primarily found?
In the blood
Where is IgA primarily found?
In mucosal secretions. Also found in serum
Where is IgE primarily found?
Bound to high-affinity Fc RI receoptor on mast cells in the skin and in the linings of GALT and BALT
Define transcytosis.
The tarnsport of molecules form one side of an epithelium to the other by endocytosis into vesicles on one side of the ell with release from the other side
Define poly-Ig receptor.
Receptor on the basolateral surface of epithelial cells that binds to and transports multimeric Igs across the apical surface of the cell
Define Brambell receptor.
A receptor on the basolateral surface of vascular epithelial cells that binds to and transports IgG from the blood into extracellular spaces.
What allows transport of maternal IgG across the placenta to the fetus?
Brambell receptors (FcRn)
What is passive transfer of immunity?
transfer of immunity to a non-immune individual by injection of a specific antibody, immune serum, or T cells. It is used clinically to protect against specific pathogens or toxins.
What is natural passive immunity?
maternal Abs transferrred to fetus via placental transfer IgG or to newborn via colostrum/breast-milk (IgA)
At birth, what type of Abs are present?
Essentially the same concentration and makeup of IgG the mother has, due to natural passive immunity. Protects for first 6-9 months of life.
What is first antibody made by all B cells? What type Ab will be first to be produced in infant?
IgM
What type of cell causes the most intense inflammatory response in the body?
Mast cells when they release their contents
What type of cell helps to kill multicellular parasites?
eosinophils.
What are B1 B cells?
subset of B cells that has a very limited receptor repertoire, and specialize in recognizing things like cell wall polysaccharides. They are the primary cell that responds to TI-2 antigens. Not present until 4-5 years of age.
Can infants respond to TD antigens (T cell dependent) and TI-1 antigens?
Yes. They have the cell types necessary to do this. T helper cells and B cells (they still lack B1-B cells though)
Is there affinity maturation in TI antigen response?
No. affinity maturation is a T cell dependent process and TI (T cell independent antigens) do no involve T cells.
Is there cell class switching in TI antigen response?
No. class switching is a T cell dependent process involved in affinity maturation and TI (T cell independent antigens) do no involve T cells.
Where do class switching and affinity maturation take place?
in germinal centers in secondary lymphoid tissue
What are the differences between folicular dendritic cells and normal dendritic cells?
follicular dendritic cells are not APCs. They instead migrate into germinal centers and trap antigens. B cells undergoing class switching will compete for binding with the trapped antigens and those that have the highest affinity are provided survival signals.
Where do most plasma cells move to after differentiating? What type of Ig would a plasma cell that migrated to secondary lymphoid tissue lining the GI tract or respiratory tract produce?
bone marrow. The exception to this are plasma cells that produce IgA and migrate to secondary lymphoid tissue in GI or respiratory tract
Where is IgG primarily found?
extracellular spaces and in serum
Where do secretory components that are sometimes found on IgA or IgM come from?
Poly-Ig receptors, when they help the Ig molecule across a mucosal surface.
What receptor allows transfer of maternal IgG to fetuses?
the Brambell Receptor (FcRn)
Which Ig molecule can pass through breast milk to an infant?
IgA
Which Ig molecule can pass through the placenta to a fetus?
IgG via FcRn (Brambell Receptor)
At what age do children’s immune system achieve full functionality?
5-6 years
What does Fc-E-RI do?
It is a receptor on mast cells that binds to IgE with high affinity and allows them to use IgE as antigen-specific receptors.
What does Fc-gamma-RIII do?
receptor found on NK cells important for ADCC
Note: they can only bind to antibodies that have bound to their antigen
What does opsonization mean?
making something easier for macrophages to endocytose
What type of Ig molecules do eosinophils use as receptors to attack multicellular organisms?
IgE, Many eosinophils will form a boundary around the invading organism
