Antibody test | The principles of ELISA (you’ll hear this term over the next few weeks).
Antibodies (immunoglobulins) are made by your immune system in response to a foreign protein (‘antigen’).
Antibodies and antigens stick directly together.
Antibodies (immunoglobulins) are made by your immune system in response to a foreign protein (‘antigen’).
Antibodies and antigens stick directly together.
An ELISA is molecular biology technique that can be used to detects these antibodies.
Imagine an empty surface, the bottom of Petri dish if you like. We’re going to start coating this surface in layers.
Imagine an empty surface, the bottom of Petri dish if you like. We’re going to start coating this surface in layers.
Layer 1 | Virus antigen. This is firmly stuck down and is going to act as a ‘capture layer’.
Layer 2 | Blood serum. This is flooded over the antigen layer and antibodies against the virus stick to the virus antigen in layer 1.
These antibodies are ‘captured’.
Layer 2 | Blood serum. This is flooded over the antigen layer and antibodies against the virus stick to the virus antigen in layer 1.
These antibodies are ‘captured’.
So now we have two layers on our dish - a layer of antibodies stuck to a layer of virus antigen stuck to the dish.
Layer 3| Antibody detector. A molecule that can bind to the antibody (that is itself bound to the antigen).
Layer 3| Antibody detector. A molecule that can bind to the antibody (that is itself bound to the antigen).
So now we have three layers on our dish - a layer of antibody detector stuck to a layer of antibodies stuck to a layer of virus antigen stuck to the dish.
Final step | The detection molecule can cause a colour change in a specific chemical.
Final step | The detection molecule can cause a colour change in a specific chemical.
So we wash that chemical over the dish.
If we see a colour change, there must be antibody detection molecules present. Therefore, there must be antibodies present. And the only antibodies that can be there are those able to bind the virus antigen.
Simple!
If we see a colour change, there must be antibody detection molecules present. Therefore, there must be antibodies present. And the only antibodies that can be there are those able to bind the virus antigen.
Simple!
ELISA | Enzyme-linked immunosorbent assay.
Enzyme-linked | The antibody detection molecule is linked (chemically bound) to an enzyme in this case, to catalyse the colour change).
Immunosorbent | Absorption of immune system molecules to insoluble states.
Enzyme-linked | The antibody detection molecule is linked (chemically bound) to an enzyme in this case, to catalyse the colour change).
Immunosorbent | Absorption of immune system molecules to insoluble states.
And just because I’m nice... 
Home bloodspot kit | Imagine those virus antigens on the end of a dipstick/in a pregnancy test style cartridge.
Add a drop of blood.
Add the antibody detection molecule + colour chemical.
Wait for colour change.
Add a drop of blood.
Add the antibody detection molecule + colour chemical.
Wait for colour change.
