Lecture 13 Flashcards
What substance produced by plasma cells mediates the humoral immune response? (don’t overthink it)
antibodies!
In cross linking, what phosphorylates ITAMs?
Blk, Fyn, or Lyn
What happens after the ITAMs are phosphorylated?
Syk binds to the ITAMs and becomes activated leading to changes in gene expression in the B cell
In addition to cross-linking, what else is necessary for sufficient B cell activation?
Signaling from a B cell co-receptor such as CR2, CD19, CD81
What part of the B cell co-receptor will bind complement?
CR2
Both B cell activation by surface Ag and soluble Ag result in what?
changes in gene expression in the nucleus
What is the second signal Tfh cells send to activate B cells?
CD40L on Tfh binds CD40 on B cell
What’s the third signal Tfh sends to activate B cells?
release of cytokines like IL-6, TGF-beta, and/or IL-4
In what organs are Ag trapped in?
Lymph nodes and spleen
What do subscapular sinus macrophages express?
CR1 and CR2
What is an important characteristic of SSmacrophages that makes them different from regular macrophages?
poor endocytic and lysosomal activity
What are the three important characteristics of Follicular DCs?
- nonphagocytic
- nonhematopoietic
- extra long processes for trapping Ag
Naive B cells bind to ___s in the _______ ________
FDC; primary follicle
Naive T cells bind to __s in the _ ____ ____
DC; T cell area
What happen between the Ag activated B cells in the T cell area and the Tfh cells?
The B cells present the Ag to Tfh cells, and they bind, forming cognate pairs
What are the three signals necessary for B cell activation?
- BCD cross-linking and co-receptor engagement
- CD40L on T cells binding CD40 on B cell
- cytokines from Tfh cell
What happens in the conjugate pairs?
Tfh synthesizes cytokines and CD40 ligands and reorients its cytoskeleton and secretory apparatus to secrete cytokines to the B cell
What is the primary focus of B cell expansion?
Cognate pairs move to medullary cords to proliferate and some B cells differentiate into IgM secreting plasma cells
What happens when cognate pairs return to the primary follicle? (2nd focus for B cell expansion)
a germinal center is formed and the Ab is made more efficient via affinity maturation and class switching
What happens to a germinal center centrocyte with low-affinity surface immunoglobulin?
No cross-linking so centrocyte can’t present Ag to Tfh and ends up dying by apoptosis
What happens to centrocytes with high-affinity surface immunoglobulin?
B cell is cross-linked and Ag gets presented to Tfh so the centrocyte gets a survival signal and divides to become plasma cells
Explain the cyclic re-entry model.
It’s a repeated process of mutation and selection where centroblasts in the dark zone undergo somatic hypermutation to become centrocytes in the light zone that compete to bind Ag. If they bind, they go back to the dark zone and become a centroblast again
cyclic re-entry of dark cells into the dark zone is dependent on re-expression of _____
CXCR4
What is the main enzyme needed for class switching?
AID
