What is an antibody?

Structure of an antibody

A typical antibody, or immunoglobulin, is a Y-shaped protein built from four polypeptide chains — two identical heavy chains and two identical light chains. The two tips of the Y contain variable regions that differ between antibodies and form the antigen-binding sites, while the stem is relatively constant. This architecture lets the immune system generate an enormous diversity of binding sites from a shared structural framework.

Antigen binding and specificity

Antibodies work by binding tightly and specifically to their target antigen — often a particular region, called an epitope, on a larger molecule. The shape and chemistry of the variable regions determine which antigen an antibody recognises.

This lock-and-key specificity is the basis of the antibody’s biological role in recognising foreign material, and it is exactly the property that makes antibodies so useful as precise detection tools in the laboratory.

Monoclonal and polyclonal antibodies

Antibodies used in research are described as monoclonal or polyclonal. Monoclonal antibodies are identical molecules that all recognise the same single epitope, produced from a single clone of antibody-producing cells. Polyclonal antibodies are mixtures that recognise several epitopes on the same antigen. The choice between them depends on the experiment’s need for specificity, consistency, or robustness.

Antibodies as research reagents

Beyond their role in immunity, antibodies are fundamental reagents in the life sciences, used to detect, label, and purify specific molecules in techniques such as immunoassays and microscopy. Reproducible research depends on careful, standardised reporting of which antibody was used, including catalogue and identifier information. This page describes the science and research use of antibodies and does not provide medical advice.