Primary and secondary antibodies
Primary and secondary antibodies are two groups of antibodies that are classified based on whether they bind to antigens or proteins directly or target another (primary) antibody that, in turn, is bound to an antigen or protein.
A primary antibody can be very useful for the detection of biomarkers for diseases such as cancer, diabetes, Parkinson’s and Alzheimer’s disease and they are used for the study of ADME and multi-drug resistance (MDR) of therapeutic agents.
Secondary antibody is especially efficient in immunolabeling. In immunolabeling, the primary antibody's Fab domain binds to an antigen and exposes its Fc domain to secondary antibody. Then, the secondary antibody's Fab domain binds to the primary antibody's Fc domain. Since the Fc domain is constant within the same animal class, only one type of secondary antibody is required to bind to many types of primary antibodies. This reduces the cost by labeling only one type of secondary antibody, rather than labeling various types of primary antibodies.
Secondary antibodies are used in many biochemical assays  including:
- ELISA, including many HIV tests
- Western blot
- "Secondary antibody review based on formal publications". secondary-antibody.com. Retrieved 2008-04-16.
- Conjugated Secondary Antibodies