Immune System - Lecture 4 Part A Flashcards
Where are B cells produced?
In the bone marrow
What are B cells responsible for?
The humoral immune defense or the antibody mediated immune response
What do B cells differentiate into?
Effector plasma cells
What are Effector Plasma Cells?
Differentiated B cells that are antibody producers
What receptor do B cells have on them?
B cell receptor (BCR)
What is different about the B cell receptors (BCR)?
The BCR is actually an antibody that is bound to its membrane
What is the Coreceptor that B cells have?
CD21
What does CD21 of B cells do?
Binds to complement proteins C3B
What does the binding of the CD21 coreceptor of B cells to C3B do?
Opsonizes the antigen increasing the strength of the binding between the B cells and the antigen
With B cells what is an antigen bound to?
The antigen is simultaneous bound to the B cell receptor (BCR) and indirectly by CD21
What happens once the B cell is activated?
Signal transduction happens, leading to antibody productions
What do B Cell Receptors (BCRs) consist of?
Four polypeptide chains
•Two identical light chains
•Two identical heavy chains
What do both the light and heavy chains of BCRs have?
Variable and constant amino acid sequences
Which region of BCRs are where the antigen binds?
The variable regions
What makes B cells antigen specific cells?
Their variability based on which antigen it binds
How long does maturation of B cells take?
One to two weeks
What do stromal cells found in the bone marrow do?
Support B cell development by producing cytokines and chemokines
What do Hematopoietic cells turn into in regards to B cells?
Pro-B cells
What do Pro-B cells turn into?
Pre-B cells
What happens during the Pre-B cell development stage?
Cells that express the BCR survive and cells that do not express the receptor die by apoptosis
What do the surviving cells of the Pre-B stage do?
Generate a pool of daughter cells with the same heavy chain but a light chain that undergoes DNA arrangement
What accounts for the variability of the antigen binding site in B cells?
The DNA arrangement that the light chain undergoes in the pre-B stage
What happens once the DNA arrangement of the light chain on Pre-B cells is complete?
The IgM receptor is expressed on B cells and the cell becomes an immature B cell
When does a cell become an immature B cell?
When the IgM receptor is expressed on them
What happens once immature B cells express IgM?
The immature B cells leave the bone marrow and migrate towards the spleen where they go to complete their maturation
Where do immature B cells complete their maturation?
In the spleen
What do immature B cells develop in the spleen to make them mature?
The IgD receptor
What does the ability of B cells to respond to antigens depend on?
IgM and IgD
What is a mature B cell positive in?
IgM and IgD
Why is B cell development simpler than T cell development?
Because B cells can recognize unprocessed antigens so they don’t need to be on an antigen presenting cell or MHC molecule
What must mature B cells be tested for?
Their affinity for self antigens
Why do B cells need to be checked for their affinity for self antigens?
To prevent autoreactive antibodies from being produced
In which part of the body does the checking for autoreactive B cells occur?
In the bone marrow
What would occur if a B cell has a strong affinity for self antigens?
The B cell will undergo receptor editing
What is receptor editing?
Changing the light chain of the BCR to change the specificity of the antigen so that it won’t be autoreactive
What happens if receptor editing of a B cell fails?
The cell will receive death signals and die by apoptosis
What happens if the B cell recognizes self antigens with low avidity?
The B cell will survive but the antigen receptor expression is reduced and the cell will become anergic
What type of antigens are B lymphocytes activated by?
A wide variety of antigens, including polysaccharides, lipids, nucleic acids and even small chemicals
What are the two ways that B lymphocytes can be activated?
- T cell dependent activation
* T cell independent activation
How does T cell dependant activation of B cells work?
A naïve CD4+ T cell or T helper cell being activated by an antigen presenting cell differentiates into an effector cell. The naïve B cell binds to the same antigen on the T helper cell and begins displaying the same antigen through MHC II and the engagement of T and B cells stimulates the proliferation and differentiation into plasma cell which will secrete IgM antibodies
What happens after activated B cells differentiate into plasma cells and secrete IgM antibodies?
Some cells will migrate back to germinal centers and proliferate a more specialized body’s response. This is when genetic rearrangement occurs
What is class switching in B cell activation?
When other class of B cell antibodies are produced for more high affinity antibodies
What is the outcome of the T cell dependent B cell activation?
A highly specialized process with the production of high affinity antibodies to eliminate pathogens
What is Class Switching in T Cell Dependant - B cell activation induced by?
T helper cells
What is Class Switching?
The process of changing the isotype of the antibody produced
What does the process of isotype switching do?
Increases functional capabilities of the humoral immune response
What is changed is Isotype switching?
The heavy chain
What is T cell independent B cell activation usually triggered by?
Polysaccharides and lipids and other non protein antigens
What is one type of T cell independent B cell activation using C3B?
When the complement system is activated by a pathogen the pathogen becomes coated with C3B which is recognized by the B cell coreceptors
How does T cell independent B cell activation occur using PRRs?
Toll-like receptor membranes recognize PAMPs which leads to B cell activation. However a lot of antigens is required for this and low affinity antibodies are produced
What do Memory B cells do?
Circulate in the cells and don’t react unless the antigen
What do Memory B cells do?
Circulate in the cells and don’t react unless the antigen is reintroduced
