Immuno 10 B cell activation 1 Flashcards
What is the chemokine that attracts B-cells to follicles?
CXCL13 by follicular dendritic cells. It binds to CXCR5.
What are the stimuli that keep B-cells alive without antigen encounters?
signals from BCR and a cytokine BAFF which gives survival signals.
How do antigens reach follicular B cells?
Small antigens <70kDa reach through conduits directly.
Large microbes or Ab-Ag complexes are transported by subcapsular macrophages to follicles.
Medium sized antigens in the medullary region are transported by resident dendritic cells (without editing the antigen).
What are the antibodies on the surfaces of naive B cells and what do they look like?
IgM and IgD. Both are monomers with short cytoplasmic tails of only 3 a.a.
How are signals transduced in Ig-mediated signaling?
Ig-mediated signals are transduced by two other molecules, called Igα and Igβ, that are disulfide linked to one another and are expressed in B cells noncovalently associated with membrane Ig
What Ig types are used when B cells class switch?
IgG, IgA, IgE
How are B-cells activated and what happens then?
Binding of antigen to the receptor delivers biochemical signals to the B cells that initiate the process of activation.
The antigen is internalized and displayed on MHC 2 for CD4+ T cells.
How is a full B-cell response to an antigen induced?
other stimuli cooperate with BCR engagement, including complement proteins, pattern recognition receptors, and, in the case of protein antigens, helper T cells
What are the changes that happen inside the activated B-cells?
Class switching from M and D to E,G,A.
Entering G1, increases size, RNA, and ribosomes.
Antiapoptotic proteins like Bcl-2 are produced.
Cell may proliferate and secrete antibodies.
Increased cytokine reception.
What is the difference between the method of activation of B cells using a polysaccharide antigen and a protein antigen?
Protein antigens usually need T-cells to help the B-cells fully activate.
Polysaccharide antigens have many epitopes that the B-cell can attach to, thereby inducing full activation without T-cell help.
What is a disease caused by Bcl-2 gene damage?
a number of cancers including chronic lymphocytic leukemia.
What are:
follicular B-cells
B-1 B cells
Marginal zone B cells
Follicular B-cells: Release antibodies when activated and circulate through lymph organs.
B-1 B cells: Secrete IgMs continuously to react with lipids and polysaccharides.
IgA secreting cells in the lamina propria derive from it.
Marginal zone B cells: also continuously secrete IgMs. Found near the marginal sinus in the spleen. They are limited in diversity and respond to polysaccharides and lipids.
How do activated T and B cells meet each other?
Helper T cells that have been activated are induced to proliferate, express CD40L, and secrete cytokines. They also downregulate the chemokine receptor CCR7 and increase the expression of CXCR5 and as a result leave the T cell zone and migrate toward the follicle. CXCL13, the ligand for CXCR5, is secreted by follicular dendritic cells, and it contributes to the migration of activated CD4+ T cells toward the follicle.
BCR engagement by these antigens results in reduced cell surface expression of the chemokine receptor CXCR5 and increased expression of CCR7, which is normally expressed on T cells. As a result, activated B cells migrate toward the T cell zone drawn by a gradient of CCL19 and CCL21, the ligands for CCR7
How do T-cells bind to AP B-cells?
Bind to peptide on MHC2 while protein antigen binds to another receptor (that means at least 2 epitopes are bound).
What are haptens and their clinical uses?
Haptens are small chemicals that can be bound by specific antibodies but are not immunogenic by themselves. If, haptens are coupled to proteins, which serve as carriers, the conjugates are able to induce antibody responses against the haptens.
This can be used in the production of conjugate vaccines. A conjugate vaccine consists of a polysaccharide antigen that is conjugated to a carrier molecule
