Antibodies Flashcards
Recall the modular nature of Ig.
______________ form the antigen-binding sites of the antibodies.
Complementarity Determining Regions
Describe how immune responses are polyclonal.
An agent that elicits an immune response is an antigen. An antigen can have many targets (epitopes) for a B-cell response. Each unique B cell activated after recognising its cognate epitope is undergoing clonal expansion. For a virus, hundreds of different antibodies might be made against the different epitopes, meaning it is a polyclonal response.
Note: multiple clones can recognise different aspects of the same epitope with different properties
Recall the B-cell response to antigen.
Mention the uses of polyclonal antibodies. Mention its concerns and benefits.
Describe the mechanism to produce monoclonal antibody (mAb).
The B cells that reacts to the antigen are polyclonal. It is then fused with myeloma cells to form hybridomas. The fusion cells are then cultures in HAT medium and then selected.
After selection, hybridomas are cloned. Each clone makes a single species of Ab (monoclonal).
CDR __ and __ are encoded in the germline. CDR __ is created during rearrangement.
1, 2
3
The CDR3 is made up of which gene segment?
The variable region of the H chain - a little bit of the V and J, and all of the D
Mention the biomedical uses for monoclonal antibodies (mAbs)
Mention the shortcoming of first-generation mouse mAbs.
It is very specific and has a high affinity, but seen as foreign in humans (rejected after multiple usage). It also has a short serum half-life. It also lacks some important effector functions in human as the constant region are mouse-derived.
Describe the mechanism of humanising a rodent mAbs.
This is possible due to the modular nature of Ig. Humanisation can also be done through CDR grafting.
Mention the two mechanism to make fully human mAbs from humans.
mABs from immune people can identify ____________________ and __________________________.
targets of protective antibody (identify new epitopes and define the structure for neutralisation)
strategies for vaccine development (in the end, make vaccine constructs that elicit only certain Abs)
Describe the characteristic of germinal centres.
GCs are sites within secondary lymphoid organs where mature B cells proliferate, differentiate, and mutate their antibody genes (through SHM) during a normal immune response to an infection. These develop dynamically after the activation of B cells by T-dependent antigen.
- formed by =< 20 B cells with extensive proliferation
- Contain B cells (90%)
- CD4+ Helper T cell (5%)
- Follicular Dendritic Cells (1%)
Recall the selection process of B cells in the germinal centre.
Upon receiving an unidentified stimulus, the maturing B cells (centroblasts) migrate from the dark zone to the light zone and start to express their antibody on the cell surface and at this stage are referred to as centrocytes.
The centrocytes are in a state of activated apoptosis and compete for survival signals derived from FDCs and TFH cells. This rescue process, known as germinal center selection, is believed to be dependent on the affinity of their surface antibody to the antigen. Such that, a B cell that has successfully gained mutations that confer a higher affinity surface antibody towards antigen gains a survival advantage over lower affinity B cell clones and those that have gained deleterious mutations.
Describe the different type of virus vaccines.
Explain why HIV vaccine development failed.
One reason is due to the accumulation of mutations in HIV over the course of the infection. This helps the virus escape from immune surveillance.
Another reason is that the main mode of infection of HIV is through the CD4 T helper cell, which induces B cells to drive antibody production. Hence, it renders the patient immunocompromised.
Describe the mechanism of HIV host-cell entry.
Viral gp120 protein binds to CD4 on the host cell. gp120-CD4 complex binds to CCR5 or CXCR4 on the host cell. Virus fuses with the host cell membrane, facilitating viral entry.
Recall the possible target sites for HIV vaccine.
Describe the mechanism of harvesting antibody via isolation from Ag-specific B cells.
Using human memory cells:
- Memory B cells of humans who have survived the disease (SARS, Ebola, HIV) are high affinity and CSR (GC-derived)
- Identify these B cells and clone the Ig genes
- Recover Ag-specific antibody that is known to function
Recall the HIV non-progressors’ immune response to HIV.
Recall the four sites of HIV which is vulnerable to neutralising by mAbs.
Recall about guided immunisation against HIV.
Recall possibly arming mAbs for improved potency.
Recall the mechanism of phage display for antibody discovery and affinity maturation.
