How does immunostaining work?

In immunostaining, special dyes, fluorescent molecules, colloidal gold particles, or color-changing enzymes may be used to label proteins. The technique is also known as immunolabeling, immunoassay, or immunodetection. 

Pathologists use immunostaining to identify a specific protein molecule and differentiate it from a mixture of other proteins in a sample of blood, tissue, or bone marrow in order to diagnose certain diseases such as cancer or infections.