Introduction of Antibodies

An antibody, also called immunoglobulin, is a protective protein produced by the immune system in response to the presence of a foreign substance. Each antibody consists of four polypeptides- two heavy chains and two light chains joined to form a "Y" shaped molecule. Within particular classes of antibodies, the stem and the bottom of the arms are fairly similar and thus are called the constant region. At the very tip of the antibody is a hypervariable region, and this hypervariable region allows the antibody to make different types of antibodies that will respond to all of the antigens that will assault the body.

Antigen-Antibody Reaction

Natural antibodies perform their biological function by recognizing all sorts of antigens. The antigens and the antibodies combine specifically with each other. This interaction between them is called antigen-antibody reaction (Ag-Ab reaction). The surface of the antibody molecule formed by the juxtaposition of the complementarity-determining regions (CDRs) of the heavy and light chains creates the site to which an antigen binds. A complementary antibody may specifically bind a site on the antigen called an antigenic determinant that can frequently be one unique structure on the antigen. All Ag-Ab bonds are weak physical bonds; covalent bonds are not encountered. The main bonds involved are Coulombic bonds, Ca2+-bridges, hydrogen bonds and Lifshitz--van der Waals bonds. The strength of interaction between antibody and antigen at single antigenic sites can be described by the affinity of the antibody for the antigen.

Antibody structure and binding. Fig.1 Antibody structure and binding. (Esmaielbeiki, 2016)

Antibody Forms

Since their first use as immunolabeling research tools in the early 1970s, antibody technologies have vastly improved, and antibodies have become critical tools for most areas of life science research. Antibodies bind specifically to a unique epitope on the antigen, thereby allowing the detection of a specific protein in an assay while avoiding detection of unrelated proteins. In addition, they emerged more recently as potent facilitators of new therapeutic approaches.

  • Primary Antibody
  • Primary antibodies directly bind to specific antigens, with high specificity and affinity, for the purposes of purifying or detecting and measuring the antigens. Primary antibodies can be monoclonal or polyclonal depending on how they are developed. Primary antibodies are typically unconjugated but also conjugated to reporter enzymes or fluorophores to aid detection or quantification of the target proteins.

  • Secondary Antibody
  • A secondary antibody aids in the detection, sorting or purification of target antigens by binding to the primary antibody. To enable detection, the secondary antibody must have specificity for the antibody species and isotype of the primary antibody being used and is generally conjugated. The most important characteristics of enzyme-labeled and dye-labeled secondary antibodies are high sensitivity and signal amplification.

Primary antibody and secondary antibody.Fig.2 Primary antibody and secondary antibody.

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For a successful experiment, it is important to have a good understanding of the primary and secondary antibodies. Based on an excellent platform and extensive experience in the development of antibodies, Creative Biolabs provides many ViroAntibody products to better serve the purpose of the experiment while saving money, time, and precious sample. Please feel free to contact us for further information.


  1. Esmaielbeiki, R.; et al. Progress and challenges in predicting protein interfaces. Briefings in bioinformatics. 2016, 17(1): 117-131.

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