B lymphocytes Flashcards
(19 cards)
Where do B cells originate from?
Bone marrow, where they mature, in the absence of antigen
They are released as naive B cells, with IgM on their surface
Which type of immunity are B cell sinvoleved in?
Adaptive and HUMORAL
Describe the adaptive immune response
Improves efficacy of innate response
Has memory cells
Requires time to develop
Second encounter with antigen is faster and stronger than the first
What are the two types of adaptive immune response and how do they differ?
Humoral - B Cell, antibody-mediated
Cell-mediated - T cells, CYTOKINES
What are the functions of B cells
Secrete antibodies
Act as memory cells
What is a mature B cell?
One that expresses IgD, in the absence of antigen
Briefly summarise the process of clonal selection
Antigen is found by complimentary antibody on B cell.
This proliferates, forming clones of the same B cell, expressing the same antibody required to neutralise antigens.
What is the BCR?
Membrane bount antibody which gives the B cell its uniqueness
What does the BCR bind to?
Part of the antigen called the epitope - SAME FOR ALL ANTIBODIES
Describe the structure of the BCR
Like an antibody, but its Fc region is too short
Leads to requirement of Ig alpha and beta components for cell communication.
How is diversity generated for BCRs?
Ig gene rearrangement - allows for BCRs to be made to combat all the various forms of microbe.
Occurs in the bone marrow
Summarise immunoglobulin gene rearragement
Separate multigene families on different chromosomes encode each chain of the BCR
In B cell maturation, gene segments are brought together.
The DNA is rearraged, spliced - (VDJ reductase removes unwanted loops) and translated to form a polypeptide chain, for the BCR
Heavy chain is dealt with first, then light chain - no D
What occurs for maturation?
B cells are taken to the periphery, where self reactive cells are apoptosed
Those that survive are mature
How are antigen-specific lymphocytes activated?
Naive B cells require both an antigen and ACCESSORY SIGNAL
Where do accessory signal sarise from? Describe the process of activation.
Microbial constituents
- thymus independent
- bacterial
- only IgM is made
T helper cell
- BCR recognises antigen
- Internalises it, processed into peptide and presented on B cell MHC Class II
- T cell recognises, migrates to lymph node and encounters B cell, activates it
- T-helper cell secrete lymphokine that makes B-cell enter cell cycle and undergo monoclonal proliferation
- Plasma cells form upon differentiation - secre BCR sa antibodies
- Or, memory cells form
What are the fates of a B cell upon meeting an antigen?
Form plasma cells or memory cells
ENTER Somatic hypermutation
and Affinity maturation
What is Ig class switching
Where T cell secretes cytokines that induce a change depending on what is needed.
- Gene segments in constant region are rearranged
What is somatic hypermutation and affinity maturation?
AID enzyme bind supon antigen binding
CG bonds are switch to AT, so AB can bind stronger.
Differentiate between primary and secondary response
primary is IgM, secondary is driven by class-switch - IgM is now IgG
