Antibodies are an important tool for demonstrating both the presence and the subcellular localization of an antigen. Cell staining or Immunofluorescence (IF) is a very versatile technique where if the antigen is highly localized, it can detect as few as a thousand antigen molecules in a cell. In some circumstances, IF may also be used to determine the approximate concentration of antigen, especially by an image analyzer.
The difference between Immunohistochemistry (IHC) and IF is with the method of detection. IHC utilizes enzyme-conjugated antibodies with enzymatic substrates and is viewed under light microscopy. IF utilizes fluorochrome conjugated antibodies and is viewed on a fluorescent microscope. IF can be divided into four steps: cell preparation, fixation, application of antibody, and evaluation.