Adaptive immunity Flashcards
B and T cells site of development
B cells- bone marrow
T cells- thymus
Production of B and T cells
B cell production throughout life in BM
T cells
- decrease in thymus at puberty
- in adults new T cells generated in extrathymic sites, long lived peripheral T cell pool
B and T cell development
Both guided by stromal cells
T cells: development is compartmentalised
B cells: stromal cells in the bone marrow
Both involve cell death via apoptosis
1st phase of B cell development
Generation of Ag receptor
V(D)J gene rearrangement -> antigen receptor
2nd phase of B cell development
Refinement of Ag receptor repertiore
- Ag receptor tested for Ag recognition
- positive selection: for Ag receptor that recognises self Ag weakly
- negative selection: for Ag receptor that binds strongly to self Ag’s, cells eliminated via apoptosis
3rd phase of B cell development
Stimulation by foreign Ag
- clonal selection of lymphocytes
- generation of effector and memory lymphocytes
T cell independent responses
Simple, repetitive antigens
Mostly IgM
Modest affinity
No memory
B cells activated by direct BCR crosslinking
B cells can also be activated via Toll-like receptors
Stages of B cell development
Organisation of lymphoid organs
T-independent B cell activaiton
T-cell/ B-cell collaboration
Class switch recombination
T cell/ B cell collaboration
Required for antibody response to complex antigens- proteins, lipids
Requires direct, physical B-T interaction
Involves multiple cell surface receptors on T and B cells
Both B and T cell must recognise antigen
Both B and T cells need signal 1 and signal 2
T cell dependent B cell response sequence of events
Antigen binding to BCR provides signal 1 to B cell
Antigen is internalised, processed and antigenic peptides are displayed on MHC for T cell recognition
Th recognises MHC complex via T cell antigen receptor, provides signal 1 to T cell
CD80/CD86 on B cell binding to CD28 on T cell provides signal 2 to T cell
T cell activation leads to upregulation of CD40L which bind to CD40 providing signal 2 to B cell
Cytokine production by activation T cell also help to activate B cell
B cell proliferates and differentiates into antibody secreting B cell
Antigen recognition by B cells vs T cells
Both form antigen receptors by V(D)J recombination
B cell receptor consists of 2 HC and 2 LC
T cell receptor consists of aB heterodimer
Both signal by associating with signalling complex in membrane
- Ig alpha and Ig beta for B cells
- CD3 complex for T cells
B cells can bind intact protein antigen in solution
T cells bind peptides displayed on the surface of another cell: and antigen presenting cell
Primary antibody response
Lag after immunisation: usually 5-10 days
Peak response: smaller
Antibody isotype: usually IgM>IgG
Antibody affinity: lower average affinity, more variable
Secondary response
Lag after immunisation: usually 1-3 days
Peak response: larger
Antibody isotype: relative increase in IgG and under certain situations IgA or IgE
Antibody affinity: higher average affinity
