Primary and secondary antibodies

This article is about direct or indirect binding. For grouping according to time of debut, see Regular and irregular 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.

Primary

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.

File:Primary-Secondaryantibody.svg

The primary antibody (in purple) binds to an antigen (in red). A labeled secondary antibody (in green), then binds to the primary antibody. The label is then used to indirectly detect the antigen.

Secondary

Secondary antibody is especially efficient in immunolabeling. In immunolabeling, primary antibody's Fab domain binds to an antigen and exposes its Fc domain to secondary antibody. Then, secondary antibody's Fab domain binds to the primary antibody's Fc domain. Since antibody's 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.

Applications

Secondary antibodies are used in many biochemical assays including:

• ELISA, including many HIV tests
• Western blot
• Immunostaining
• Immunohistochemistry
• Immunocytochemistry

References

• Conjugated Secondary Antibodies [1]