Lecture 28 - B Cells. Flashcards
Where do B cell interactions happen?
- B cell activation, differentiation, and proliferation all occur in lymph node.
- But each step takes place in a different part of the lymph node.
- B cells migrate to different regions of the lymph node during different stages
- There are signals that direct the B cells to the appropriate location at each different stage.
What takes place in Subcapsular Sinus?
Where SCS macrophages are located and where they encounter Ag.
What takes place in T Cell Zone?
Where T cells get activated by interacting with DCs.
What takes place in B cell zone?
- Where B cells encounter Ag and undergo later stages of proliferation and differentiation, including in B cell follicles and Germinal Centers.
- B cells receive signal 1
SSM = SCS macrophage.
What takes place in T-B Border?
Border between the B and T cell zones. This is where B cells first receive “signal 2.”
What takes place in the Germincal center and Follicles?
- Follicle: Development of B cells, where they get activated.
- Germinal center: Site of intense B cell proliferation and differentiation.
What happens when a B cell encounters an antigen (Ag) on SCS macrophages, free-floating Ag, or follicular dendritic cells (DCs) in the B cell zone?
- B cell receptor (BCR):Ag is internalized & processed
- Increased expression of MHC II
- Increased expression of chemokine receptor, which targets the B cell to the T-B border
- At the T-B border, the B cell receives signal 2 and becomes activated.
What are the two choices that the Activated B cell has?
- Form primary focus in sub-capsular region.
- short-lived plasmablasts arise. - Migrate to follicle to form Germinal Center.(GC reaction)
- Plasma cells secrete Ab with higher affinity.
(plasmablasts and Plasma cells are NOT the same)
What are the two main outcomes of Primary Focus?
- Plasmablast: Early antibody production (mainly IgM)
- IgM+ Memory B Cell: Production of IgM.
Plasmablasts
- B cells that secrete antibody
- Responsible for early antibody production
- IgM produced
- Most plasmablasts in primary focus die by apoptosis within 5-10 days
- Some plasmablasts can migrate to the bone marrow and become plasma cells, where they continue antibody production.
Where does an activated B cell migrate after receiving signal 1 and signal 2?
The activated B cell migrates to form a primary focus near the subcapsular zone, interfollicular regions, or medullary cords.
What happens to activated B cells in the primary focus?
In the primary focus, activated B cells undergo proliferation and differentiate into plasmablasts.
When do primary foci become apparent during a primary infection?
Primary foci are apparent about 5 days after a primary infection.
What are the two main outcomes for Secondary Lymphoid follicle (germinal center)?
- Plasma cell (secrete large quantities of antibodies)
- Secretes Ab with higher affinity. - Memory B Cell (important for memory response - maintain capacity to produce higher affinity antibodies)
What is the secondary lymphoid follicle also known as?
The secondary lymphoid follicle is also known as the Germinal Center.
What happens when B cells enter the Germinal Center?
B cells receive signals 1 and 2 again, undergo differentiation, and produce antibodies that are more effective and have higher affinity through processes like somatic hypermutation, affinity maturation, and class switching.
When does the size of the germinal center peak after antigen stimulation?
The size of the germinal center peaks 7-12 days after antigen stimulation.
What do plasmablasts and plasma cells secrete?
Plasmablasts and plasma cells secrete antibodies. Plasmablasts mostly stay in the lymph node to produce early antibodies with lower affinity, mostly IgM.
What is the difference between plasmablasts and plasma cells in terms of location and antibody production?
- Plasmablasts: Mostly stay in the lymph node to produce early antibodies (lower affinity, mostly IgM).
- Plasma cells: Can stay in the lymph node (medulla) or travel to the bone marrow to produce antibodies later with higher affinity, after class switching (not IgM).
Can plasmablasts and plasma cells migrate to the site of infection?
Yes, both plasmablasts and plasma cells can migrate to the site of infection to produce antibodies.
