Adaptive immunity - B cells activation + antibodies Flashcards
What are B-cell? Where do they encounter antigens? How do they display MHCll?
-lymph node recirculating B cells encounter antigen which has drained from the tissue.
- B cell recognise antigen via B cell receptor > Phagocytosis
- Phagosome fuses with lysosome > break down antigen > peptides are then loaded onto MHCII
- MHCll sent to surface of cell
How do Activated Follicular T helper cell activate B cells?
(Junction between B and T cell zone )
- Activated CD4* follicular T helper cell recognise the antigen presented by the B cell on MHCII via receptor
- Binds to co stimulatory molecules
- Binding of CD40L> CD40 sends signal to B cell to proliferate
- The activated T helper cell releases cytokines > instruct B Cell to undergoes class switching
- Cytokine produced determines what antibody the B cell will produce
- B cells mature into plasma cells and start to produce specific antibodies.
What is the general structure of an antibody?
- Two chains : Heavy and light chain
- Variable region : recognise pathogen
- Constant region : Recognised by Fc receptors on other immune cells and gives antibody its function (Different cells have different Fc receptors to recognise bound antibodies)
Which antibody is the B-cell receptor?
- IgD molecule
What are the different types of antibodies?
IgM : Does not require T cell help to be produced (PENTAMER)
IgG: Th1/2 responses
IgE: Larger pathogens can’t be phagocytosed/ allergy
IgA: Th2/ mucosal surfaces as dimer
After initial interactions where do some of the B and T cells go?
-medullary cords and proliferate producing mostly IgM to provide an early antibody response
-Others move to form a germinal centre
What happens in the germinal centre?
- Following activation the B cell moves into the B cell zone and starts to proliferate in dark zone of GC (centroblast) > undergo somatic hypermutation
- While proliferating they continue to receive signals from T cells through CD40L > CD40 ligand interactions to sustain proliferation.
- B cells move into light zone of GC and are tested by follicular dendritic cells for recognition of the antigen by the antibodies they are producing
(after proliferating B cells are termed centrocytes) - If they recognise the antigen with high affinity they: mature into plasma cells and leave the germinal centre to produce large amounts of antibodies used in adaptive immune response.
OR some of the B cells will become Memory B cells - If the B cell has low affinity for the antigen i.e antibodies its producing are ineffective it undergoes apoptosis and is phagocytosed by a tingible body macrophage
What is somatic hyper mutation?
(Process 1 needed for high affinity antibody)
- Many mutations occur in the Variable gene region of the activated B cell receptor - to make very specific antibody, stronger more specific response to antigen
> The T follicular helper cells are constantly interacting with the B cell to check the receptor function and provide signals to carry on proliferating
What is class switching?
(Process 2 needed for high affinity antibody)
- B cell changes the transcription of its genes to pair the variable region with a different constant region
> Under the influence of different cytokines released by T helper cell > B cells can start to produce antibodies with different constant region
How are antibodies involved with complement activation?
How are antibodies involved with opsonisation?
-Without an opsonin, such as an antibody, the negatively-charged cell walls of the pathogen and phagocyte repel each other.
How do antibodies sensitise for killing by NK cells?
What are antibodies involvement in neutralisation?
How do antibodies Sensitise mast cells and activating eosinophils?
What is T cell independent B cell activation?
- Produce antibodies early in an infection
There are two ways this is possible:
1.Mature plasma cells reside in some barrier tissues of the body producing antibodies e.g. IgA in the gut epithelium
2. Specialised B cells in the peripheral tissues and can be activated independently of T cells by dendritic cells.
Specialised B cells in the peripheral tissues and can be activated independently of T cells by dendritic cells. What are the 2 ways this is done?
