(10) B-cell mediated Response Flashcards
(56 cards)
What is the 1st step in B cell activation?
- B cell encounters antigen and Ig-alpha:Ig-beta crosslink and transduce a signal to the nucleus indicating the cognate determinant has been found
- CR2 binds C3d (from C3b) which confirms the pathogenic nature of the initial Ig-alpha:Ig-beta signal
**Note: this alone is not sufficient to activate the B-cell
What is the function of CD19?
- CD81?
CD19 amplifies the transmission of the Ig-alpha:Ig-beta signal
Differentiate T-dependent and T-independent reactions of a B-cell?
T-dependent requires binding of cognate AS WELL AS T-cell binding
- This leads to proliferation
T-independent reactions require B-cell Receptor (BCR) and a PRR on the B-cell be bound by cognate and PAMP respectively
**THIS DOES NOT LEAD TO GERMINAL CENTER RXNS
What are the two types of T-independent antigens?
- how do they differ?
T-independent 1 (TI-1)
- binds PAMP and BCR to initiate B-cell response
T-independent 2 (TI-2)
- bind Polysaccharides (repetitive structures in general)
What are mitogens?
T-independent 1 (TI-1) antigens
Determine if binding of TI-1 causes the following:
- Germinal Center Reaction
- Class Switching
- Proliferation
- Antibody Release
Germinal Center reaction:
- NO, B-cell activation by TI-1 (or TI-2) does not lead to a germinal center reaction
Class Switching:
- NO, not really… some switching to IgG, but mostly just IgM produced
Proliferation:
- YES!!! cell still proliferates
Antibody Release:
- YES
What happens if a huge number of Mitogens (TI-1) are encountered?
B-cells proliferate in a polyclonal fashion aka a NON-SPECIFIC RESPONSE
What are antigens that might elicite a TI-1 response?
LPS
Pokeweed
What constitutes a TI-2 antigen?
- how does it work?
- what (cell type) does it work on?
TI-2 antigen:
- Repetitive structure like polysaccharides
How:
- Repetitive structures and cause a lot of cross-linking of BCRs
What:
- Works mostly on B1 B cells
Which of the following antigens can elicit and antibody response in the absence of Cognate T cells?
- TI-1
- TI-2
- TD
YES:
- TI-1
- TI-2
NO:
- TD
**This is the definition of a T-cell dependent reaction
Which of the following antigens can cause antibody production in congenital athymic individuals?
- TI-1
- TI-2
- TD
YES:
- TI-1
- TI-2
NO:
- TD
**The thymus is needed for T-cell production, if people lack a thymus they can’t do T-dependent activation, but should have no problem with T-dependent activation
Which of the following antigens can elicit and antibody response in infants?
- TI-1
- TI-2
- TD
YES:
- TI-1
- TD
NO:
-TI-2
**TI-2 can’t elicit a response in infants because these antigens mainly affect B1 B cells, which aren’t finished maturing until we are about 5 y/o
Which of the following antigens can activate T cells?
- TI-1
- TI-2
- TD
YES:
- TD
NO:
- TI-1
- TI-2
**If the antigen is T-dependent it must also be able to bind T-cells
Which of the following antigens induces immunological memory?
- TI-1
- TI-2
- TD
YES:
- TD
NO:
- TI-1
- TI-2
Which of the following antigens can activate non-specific B-cells?
- TI-1
- TI-2
- TD
YES:
- TI-1
NO:
- TD
- TI-2
**remember TI-1 also known as mitogens which can induce a nospecific response in high enough concentrations
Which of the following antigens REQUIRES repeated epitopes?
- TI-1
- TI-2
- TD
YES:
- TI-2
NO:
- TD
- TI-1
**This defines TI-2 binding
What type of response would you expect to be initiated by the presence of flagellin?
- TI-1 or TI-2
TI-2 this is because flagellin is highly repetitive
What type of response would you expect to be initiated from:
- LPS?
- Polysaccharides?
LPS = TI-1
Polysaccharides = TI-2
What cell types are involved in the germinal center?
B and T HELPER cells
What happens during a germinal center reaction?
- B cell receives both of its signals in 2˚ lymph. tissue (TH1 or TH2 binding and antigen binding)
- activated cell proliferates and undergoes somatic HYPERMUTATION
- Positively selected cells undergo isotype switching
What actually creates the germinal center?
After the germinal reaction some B cells and T cells that were positively selected will migrate back into B cell zone to proliferate to create germinal center
**NOTE: B cells that do not reenter will be Plasma cells
Describe what happens to a B cell proceeding the germinal reaction to the point where it undergoes isotype switching?
- What is going on and where??
- B cells hypermutate in germinal center (via somatic hypermutation)
- B cells here = CENTROBLASTS - B cells move toward periphery
- B cells here = CENTROCYTES - B cells encounter FDCs (follicular dendritic cells) which positively select for high affinity B cells (AFFINITY MATURATION)
- B cells enter T-cell zone and T cells promote ISOTYPE SWITCHING
How do follicular dendritic cells work in the process of affinity maturation?
They expression lots of:
- Fc receptors:
- Traps things bound by antibody
- Complement Receptors
- Traps things bound by complement
*It presents the shit that its bound and sees which B cells want it the most, those that do are given survival signals, those that don’t DIE
What is the difference in FDCs and normal dendritic cells?
Normal dendritic cells present peptides to Naive T cells to induce differentiation.
