Primary and secondary antibodies
Primary and secondary antibodies are two groups of antibodies based on whether they target a target of interest directly or target another (primary) antibody that, in turn, is bound to a target of interest.
Primary antibodies are antibodies raised against an antigenic target of interest (a protein, peptide, carbohydrate, or other small molecule) and are typically unconjugated (unlabelled). Primary antibodies that recognize and bind with high affinity and specificity to unique epitopes across a broad spectrum of biomolecules are available as high specificity monoclonal antibodies and/or as polyclonal antibodies. These antibodies are useful not only to detect specific biomolecules but also to measure changes in their level and specificity of modification by processes such as phosphorylation, methylation, or glycosylation. 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.
A secondary antibody is an antibody that binds to primary antibodies or antibody fragments. They are typically labeled with probes that make them useful for detection, purification or cell sorting applications.
Specific secondary antibodies are usually chosen to work in specific laboratory applications. Frequently, any one of several secondary antibodies perform adequately in a particular application. They are selected according to the source of the primary antibody, the class of the primary antibody (e.g., IgG or IgM), and the kind of label which is preferred. Identifying the optimal secondary antibody is normally done through trial and error.
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