5. Adaptive Immune Response: B Cells Flashcards
Which immune cells produce antibodies?
B cells and only B cells (plasma cells too but they’re derived from B cells)
Where are B cells produced and matured?
The bone marrow
What is a naive B cell?
B cell which has not yet met an antigen
What is the difference in receptor of B and T cells?
B cells use antibody as receptor whereas T cells use T cell receptor
What are the five classes of antibody?
IgM, IgA, IgE, IgD, IgG
What are the two initial classes of antibody produced are present on the B cell surface?
IgM and IgD (both specific for the same antigen) - 50,000 copies of each
What else is expressed on the B cell surface other than transmembrane version of antibodies?
Ig-alpha, Ig-beta, CD19 (B cell marker), CD20, CD40 (not present only on B cells)
What is another name for the transmembrane version of the antibody present on the surface of the B cell?
BCR (B cell receptor)
What is the structure of the BCR?
Contains variable (recognises native/natural antigen) and constant regions
How does the BCR recognise antigen?
Recognises the natural form of the antigen (unaltered), just binds it as it flows past
How many different BCR variable regions are possible with gene rearrangement?
10^15
What is clonal selection?
The antigen selects the most appropriate B-cells and then those proliferate in an infection
What do most B cells differentiate into? What does this cell do?
Plasma cells, secrete correct antibody
How are plasma cells different structurally to B cells?
Large amounts of cytoplasm, rough endoplasmic reticulum and mitochondria so they can pump out lots of proteins (antibodies)
What do some of the B cells differentiate into?
Memory cells (smaller amount)
What occurs genetically when B cell differentiates into the plasma cell?
It splices out the transmembrane region of the antibody so the antibody can be secreted/soluble
What is the benefit of using the antibodies from plasma cells derived from memory cells?
More antibodies made (as more memory cells) and due to somatic hypermutation the cells fit stronger to the antigen
Immunological memory can vary. Give an examples of diseases with long and short immunological memories
Long: Yellow fever
Short: Tetanus
What helps B cells to undergo class switching? What is class switching?
T helper cells
Class switching is the ability of B cells to produce IgG, IgA and IgE (instead of only IgM and IgD)
What is the best helper T cells for enabling B class switching?
Th2
How do T cells activate class switching?
Cell surface interactions/soluble communicators
CD80 and CD86 on B cell interact with CD28 of T cell
CD19 and CD20 (B cell markers)
CD40 of B cell interacts with CD40 ligand of T Cell
Interactions send signals into both B and T cells causing B cell to divide and proliferate
What defines the class of antibody produced by the B cell?
The type of cytokine produced by T helper cells
Give an example of a cytokine released by T helper cells which causes B cells to switch to a specific Ig?
Interleukin 4 and 13 cause B cell to class switch to IgE production
What is somatic hypermutation?
Accompanies antigen induced proliferation, involves rearranging of the variable region genes - allows you to better bind the antigen
How are the somatically hyper mutated cells selected?
If mutated B cell has little antigen stimulation then survival rates will be low, but if cells bind antigen stronger then survival rate increases
What is a professional antigen presenting cell?
Cell which shows antigen to a T cell using MHCII - B cells can do this
What is the difference between antigen presenting cells and professional antigen presenting cells?
APCs include all nucleated cells and are cells which contain MHCI for presenting antigen to T cells, professional antigen presenting cells (e.g. B cells) also contain MHCII to present antigen to T cells (this is a much more efficient method
How do B cells present antigen?
- Recognise antigen and bind it with transmembrane antibodies
- Antigen and transmembrane antibody entocytosed into cell
- This is then chopped up with proteases (from endosomes) into peptides
- This leads to a co-stimulatory signal along with the presentation of antigen in the MHCII
How is the signal of the antigen binding transduced into the B cell?
Whilst the BCR recognises/binds the antigen, it does not transduce the signal.
The signal transduction is carried out by Ig-alpha and Ig-beta associated to the BCR (not immunoglobulin molecules but associated with them), these have long cytoplasmic tails with ITAMs. ITAMs and Src family tyrosine kinases initiate signalling into the nucleus to tell the B cell to proliferate and divide
What is a T independent antigen?
An antigen that can stimulate B cells without need for helper T cell
Give an example of T-independent antigen
polysaccharide antigen - if antibody has physically repeated structure then can cross-link with others so can send signal into B cell which overcomes reliance on T cell.
But T cells required for class switching so large IgM response but no class switching
