An antibody is a glycoprotein or immunoglobulin that binds to an antigen (or part of the antigen called an epitope), this combination makes it possible to induce an immunological reaction against an external agent. An antibody is composed of constant and variable domains. The variable domains constitute the site of binding to the antigen or paratope.
Antibodies are an important tool for the study and detection of many mechanisms and pathologies.
Antibodies are produced naturally by organisms during an immune reaction but antibodies can be produced for use in research or diagnosis. They are then separated into two groups: primary and secondary antibodies.
A secondary antibody binds to the primary antibody which is directly attached to the target antigen. By exploiting this interaction, the secondary antibodies indirectly assist in the detection and purification of the target proteins (antigens). This is done by coupling the secondary antibodies with an enzyme, a fluorochrome for example for visualization by chemiluminescence or fluorescence. Secondary antibodies can also be attached to resins or beads (magnetic or silica) in order to purify the proteins of interest.
The choice of the secondary antibody depends on the origin and type of the primary antibody used. Thus if the primary antibody is an IgG made in mice, a secondary antibody directed against mouse IgG should be taken.