Lecture 24 Flashcards
What antigens cause T cell independent antibody production?
T independent antigens are highly repetitive structures e.g. flagellin, polysaccharides. This causes crosslinking between BCRs and sends a strong signal to the B cell
What antigens cause T cell dependent antibody production?
All non-repetitive antigens e.g. peptides, proteins
True or false: B cells express MHC I
False. B cells express MHC II so they can act as antigen-presenting cells to CD4 T cells
What are the steps for B cell activation when T cells produce cytokines?
- B cell receptor binds antigen/pathogen and takes it up to process it.
- Processed antigen is presented on the MHCII.
- CD4T cell activated by B cell acting as an APC
- T cells produce cytokines
- B cell responds to the cytokines by developing into plasma cells and begin producing antibody
What are the steps for B cell activation by T cells via CD40L
- B cell receptor binds antigen/pathogen and antigen is taken up and processed
- B cell presents antigen and upregulates CD40 expression
- T cell activated by B cell acting as an APC
- T cell upregulates CD40L which binds to CD40 on the B cell
- B cell develops into a plasma cell and produces antibody
Where does B cell expansion happen?
Spleen and lymph nodes
What immune cells are the main inhabitor of the paracortical area of the lymph node?
T cells
What immune cells are the main inhabitor of the lymphoid follicle in the lymph node?
Mostly B cells
Where are germinal centers found in the body?
Germinal centers are found in B cell regions of lymph nodes or spleens
What occurs during B cell activation in the lymph node? Where do the B cells go when theyre activated?
During activation, B cells encounter antigen specific T cells in the T cell areas outside of the B cell follicles. Acitvated B cells move into the follice and form a germinal center.
What types of cells make up germinal centers?
Germinal centers are mostly composed of proliferating B cells and around 10% antigen specific T cells as well as follicular dendritic cells.
Why do your lymph nodes grow when youre sick?
Because the germinal centers in the lymph nodes are growing because the B cells are undergoing clonal expansion.
What is clonal expansion?
When B cells encounter their antigen through the BCR and begin to divide into identical daughter cells.
What is somatic hypermutation? When does it occur?
Somatic hypermutation is where point mutations are introduced during clonal expansion. Occurs after the antigen driven B cell activation as a part of the gernimal center response.
What % chance at each division that a B cell will acquire a mutation in the antibody it encodes?
50%
Where are mutations introduced in somatic hypermutations?
Point mutations are introduced into rearranged V region genes at a high rate. Occurs at ‘hotspots’ in the genes.
What protein is required for somatic hypermutation?
Activation induced cytidine deaminase (AID)
What is affinity maturation?
Good mutations are introduced during somatic hypermutation. Higher affinity interaction with antigen. This causes the b cell to survive, proliferate, and mature into antibody producing cells and outcompetes B cells with lower affinity antibody/BCR.
What happens when a bad mutation is introduced through somatic hypermutation?
Bad mutations cause lower affinity interactions with antigen. Can’t compete with better B cells so they die by apoptosis.
Somatic hypermutation and antibody class switching both occur in…
The germinal centre
What are 6 functions of antibodies
- neutralisation
- opsonisation
- complement activation
- agglutination
- antibody-dependent cell mediateed cytotoxicity
- degranulation
What is antibody class switching? What happens?
When antibodies change classes e.g. from IgG to IgE.
Variable region stays the same (antibody retains the same specificity) but different isoforms of constant region of heavy chain.
What two types of antibodies are expressed on naive B cells?
IgM and IgD
What is the first antibody secreted by activated B cells?
IgM
