Explain how infection by a pathogen can be detected by an ELISA test for antigens.

Infected individual will have pathogens/antigens in bodily fluids

Test contains immobilized/fixed antibodies to the pathogen/antigen

If present, antigen binds to «immobilized» antibody/capture molecule

Solution is washed and only fixed antigen-antibody complexes persist

Then a detection antibody linked to an enzyme is added

Reacts with fixed antigen-antibody complex

A chromogenic/potentially fluorescent substance is added

Enzyme changes substance to a different/detectable colour

The presence of colour is a positive response/absence of colour a negative response

Most candidates had a fairly good idea of how to use an ELISA test to detect antigens from a pathogen although the order of steps, and antigen and antibody, were sometimes confused. This discriminated well between candidates.