B Cells Flashcards
B cells are derived from what cell type
Pluripotent stem cells in the bone marrow
When is B cell development initiated?
When the immature B cell recognizes an antigen
3 key events during B cell maturation
- Rearrangement and expression of Ig genes in a precise order
- Selection and proliferation of developing B cells at the pre-antigen checkpoint
- Selection of the mature B cell repertoire
How do B cells develop their specificity and diversity?
Through VDJ recombination
Same in B and T cell development
What happens if you have a defect in RAG
Deficient in both B and T cells since the enzyme is involved in VDJ recombination for both
What is VDJ recombination
A random combo of germline gene segments being brought together by the random addition or deletion of sequences at the junctions between the segments before they are united
Positive selction
Allows survival of useful lymphocytes
B cells that express receptors are preserved
Negative selection
Removes harmful lymphocytes that bind too strongly to self antigens
Also called central tolerance
Where do
1. Plasma cells
2. Memory cells
migrate to
- Back to the bone marrow
2. Other tissues
B cell response to T-dependent antigens
The B cell response here is dependent on T cells
Response take place in the lymphoid organs, not the thymus
Humoral response to a protein antigen
B cell response to T-independent antigens
Humoral response to a non-protein antigen (polysaccharide)
Initiated by the recognition of the antigens by specific Ig receptors of naive B cells
Signals induce B cell clonal expansion and IgM secretion
Thymus dependent vs independent for
- T cell help required
- Degree of isotype switching
- Speed of antibody production
- Affinity maturation
- Ability to make long lasting memory cells
- Yes, no
- High, low
- Slow, fast
- High, low
- Strong, weak
What is the key signal that initiates B cell proliferation and differentiation
CD40-CD40L
CD40 on B cell, Ligand on T cell
A 2 factor authentication like T cell development
2 types of antibodies
Membrane bound
Secreted
3 classes of secreted antibodies and their function
IgG, IgA, IgE
Neutralize toxins
6 roles of antibodies
Neutralization of microbes and toxins
Opsonization and phagocytosis of microbes
Antibody-dependent cellular cytotoxicity (NK cells)
Phagocytosis of microbes with complement
Inflammation
Lysis of microbes
Function of
- IgA
- IgE
- IgD
- mucosal immunity (secretions of resp and GI)
- mast cell degranulation
- antigen receptor of naive B cells
Functions of
- IgG
- IgM
- opsonization, activation of complement, cytotoxicity with NK cells, transfer across placent
- activate complement, antigen receptor of naive B cells
Somatic hypermutation
Introduction of random mutation in the variable region of the BCR during B cell proliferation
Leads to antibodies that are more efficient in binding the antigen (higher affinity)
Requires the interaction between CD40 and CD40L (so only in T dependent protein antigens)
Affinity maturation
B cells make antibodies that are better binding to the pathogen (more efficient)
Where does the T-dependent reaction take place?
In the lymphoid organs, NOT the thymus
Protein binds to naive B cells, causing recruitment of T and B cells into the germinal centers of the spleen and lymph nodes
Is somatic hypermutation seen in T-dependent or T-independent antigens?
Only in T-dependent
Because it requires the interaction between CD40/CD40L
