Antibody structure, diversity, and applications

Antibody definition and antigen specificity

An antibody (immunoglobulin) is a large immune-system protein that identifies and neutralizes specific antigens (molecules on bacteria, viruses, or infected cells). Each antibody molecule has one or more highly specific antigen-binding sites located at the tips of its “Y”-shaped structure. These binding sites recognize particular antigen features called epitopes, in a precise “lock-and-key” style interaction. Antigen specificity comes from the variable regions of the antibody, especially the complementarity-determining regions (CDRs), which form the paratope (the actual antigen-binding surface). The immune system generates vast diversity of these binding regions through processes such as V(D)J recombination, somatic hypermutation, and affinity maturation, producing antibodies with different paratopes and therefore different antigen specificities. Antibodies can also be classified by how many targets they recognize (e.g., monospecific, bispecific, or polyvalent/unspecific), and by whether they are secreted or membrane-bound (as part of the B cell receptor).

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Paratope and epitope binding

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