Immunoassay kit manufacture. Technician's gloved hands pipette fluid during the manufacture of immunoassay medical diagnostic kits. The kits contain sheep antisera made up of antibodies produced in response to exposure to human antibod- ies. An immunoassay (antigen-antibody assay) shows the presence or absence of a certain protein, such as an antigen, antibody or hormone, in a bodily fluid. For any specific antigen (foreign protein), immune systems produce an antibody that binds to it. Immunoassay tests are often used to show the presence of antibodies to an infection, a positive result producing a colour change. Photographed at Helena Laboratories in Sunderland, England.