Secondary antibody

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A secondary antibody is an antibody raised specifically, to hybridise to another antibody to then be detected. Secondary antibodies are purified from the serum of several hosts, including human, mouse, rabbit, goat, and rat. The secondary antibodies bind to the primary antibody in order to aid in sorting, purification and detection of the target antigens. The secondary antibody must have specificity to the antibody species and isotype of the primary antibody being used to ensure detection. Hence, they are usually conjugated [1]

This particular antibody is raised in an animal different to the primary antibody, for example, if the primary antibody was raised in a rabbit, the secondary antibody may have been raised in a goat, so it is an anti-rabbit antibody.The antibody in this case would be produced by injecting the primary antibody into the goat and then collecting a sample of its serum which is highly concentrated in the secondary antibody. The next stage would be to couple the antibody to a marker, whether this is a fluorescent dye or an enzyme. The marker used is very important as different detection techniques visualise different things [2].

Secondary antibodies are available with specificity for whole Ig molecules or antibody fragments such as the Fab or Fc regions. In order to identify the specific secondary antibody used is normally done based on the nature of the primary antibody as well as the detection assay. Besides that, the conjugated secondary antibodies can be normally used for protein assays such as ELISA or Western blot, and immunology analysis. In addition, IgG is the predominant antibody in the secondary response which constitutes an important defense against viruses and bacteria

IgG is the only antibody that crosses the placenta and only its Fc part binds to receptors on the surface of placental cells. Hence, it is the most abundant immunoglobulin in newborn babies[3].


  1. Levinson W., (2012), Medical Microbiology and Immunology:12th Edition, USA:The McGraw Hill Companies
  2. Alberts. B, Johnson. A, Lewis. J, Raff. M, Roberts. K, Walter. P (2008) Molecular Biology of THE CELL:585, 5th Edition, New York, Garland Science, Taylor and Francis Group.
  3. Levinson W., (2012), Medical Microbiology and Immunology:12th Edition, USA:The McGraw Hill Companies
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