Adaptive immunity 1 Flashcards
Features of adaptive immune response compared to innate
Slower response
The receptors have an initially low affinity to receptors they encounter in primary response.
Has memory
Receptors are created via gene rearrangement.
Lifespan of naive B cells
5 Days, mature B cells have a much more longer lifespan
T cells production
Number produced peaks in puberty then declines.
Due to the longevity of the cells.
Positive selection of antigen receptors
Part of refinement of antigen receptor repitore
This is where self antigens are recognised during B and T cell production.
Antigens with weak affinity are selected.
Negative selection of antigen receptors
Part of refinement of antigen receptor repitore
T and B cells with high affinity for self antigens are destroyed.
Types of B cell antigens
T cell-dependent
- Make up more of the B-cell antigens
- Usually proteins
T-cell independent
- Usually lipids, polysaccharides on bacteria.
Steps in T and B cell activation (T-cell dependent)
- Antigen binds to B-cell receptor
- Produces Signal 1 to B cell - Antigen is internalised in B cell and processed
- Displayed using MHC for T cell recognition. - T cell receptor on T cell recognise the angiten-MHC complex
- Produces signal 1 to T cell. - CD80/ CD86 receptor on B cell binds to CD28 on T cell
- Produces signal 2 to T cells to produce cytokines.
- Cytokine is typically IL-2 - T cell is activated and up-regulates CD40 ligand (CD40L) receptors–> Binds to CD40 on B cells
- Signal 2 to B cells. - T cells release cytokines and activates B cells
- Causes proliferation and differentiation to plasma cells.
Primary response
- Lag time after immunization
- Peak response
- Antibody isotype
- Antibody affinity
Lag time
- 5-10 days
Peak response
- Smaller than secondary response
Antibody isotype
- IgM, IgG
Antibody affinity
- Lower/ more variable affinity than secondary response.
Secondary response
- Lag time after immunization
- Peak response
- Antibody isotype
- Antibody affinity
Lag time
- 1-3 days
Peak response
- Larger than primary response
Antibody isotype
- Increase in IgG
- May show increase in IgA/ IgE due to heavy chain class switching
Antibody affinity
- Affinity maturation causes higher average affinity compared to primary response.
Compared B and T cell antigen recognition [4 comparisons]
Both form from V(D)J recombination
Structure
- B cells= 2 light and 2 heavy chains, secreted and membrane bound.
- T cells= alpha-beta heterodimer, only membrane bound
Signally complex
- B-cells= Ig-alpha and beta
- T cells= CD3 signal complex
Antigen binding
- B cells= intact protein antigens in solution
- T cells= peptides displayed on MHC of APC.
T cell independent response of B cells
Response to simple repetitive antigens
Mainly IgM
Modest affinity, no memory
B cell receptors crosslink when activated
- Can also be activated by TLRs
