The ELISA, or enzyme-linked immunosorbent assay, is a method used to measure antibodies, antigens, proteins, and glycoproteins. The ELISA has been used for pregnancy tests, diagnoses of infections, such as HIV, and the measurement of cytokines, or proteins secreted by immune cells in response to pathogens. The ELISA plate is coated with a capture antibody which is raised to be against the antigen being used in the experiment. Next, the researcher introduces a sample of what they're testing, like a serum or blood sample, and the antigens in that sample are then attached to the capture antibodies. Then, the researcher adds detection antibodies, which are labelled with enzymes. After, the researcher adds a type of substrate that reacts with the enzymes and turns into a colored product. From that color, the researchers can determine the antigen concentration in each sample.