What is "isotype"

Isotype can refer to:

• In crystallography, "isotype" is a synonym for isomorph
• Isotype (biology), per the International Code of Nomenclature for algae, fungi, and plants, a duplicate of the holotype.
  • Isosyntype, a duplicate of a syntype.
• Isotype (picture language), a method of showing social, technological, biological and historical connections in pictorial form.
• Isotype (immunology), any of the related proteins/genes from a particular gene family.

Isotype (International System of TYpographic Picture Education) is a method of showing social, technological, biological and historical connections in pictorial form. It was first known as the Vienna Method of Pictorial Statistics (Wiener Methode der Bildstatistik), due to its having been developed at the Gesellschafts- und Wirtschaftsmuseum in Wien (Social and economic museum of Vienna) between 1925 and 1934. The founding director of this museum, Otto Neurath, was the initiator and chief theorist of the Vienna Method. The term Isotype was applied to the method around 1935, after its key practitioners were forced to leave Vienna by the rise of Austrian fascism.

In immunology, the " immunoglobulin (AKA antibody) isotype" refers to the slight phenotypic variations within the immunoglobulin gene family that encode for variant immunoglobulin heavy chains and immunoglobulin light chains. To be an isotype of a particular gene family means to belong to a set of genes that encode functionally similar proteins. Usually, isotypes that belong to a particular gene family are duplicate copies of the same gene that arose because of a mistake during DNA replication. As the species continues to evolve, those duplicated genes are passed on from generation to generation until every member of the species has a copy. Each of those genes have since undergone mutations of their own, such that they diverge slightly in structure and function, giving rise to the different isotypes known today.

In humans, there are five heavy chain isotypes and two light chain isotypes:

• heavy chain
  • α - IgA 1, 2
  • δ - IgD
  • γ - IgG 1, 2, 3, 4
  • ε - IgE
  • μ - IgM
• light chain
  • κ
  • λ

Cells that express immunoglobulin proteins are called B cells, and the isotype that they secrete changes depending on a few variables. Some variables include exposure to antigen, interaction with T helper cells, and the composition of cytokines surrounding them. These variables all add up to mount a defensive response called the adaptive immune response. One of the main physiological changes that occurs during an adaptive immune response is a process called immunoglobulin class switching. The function of the antibody and its sub-localization within the body changes depending on the isotype class that it switches to.