Heavy-Chain Isotypic Determinants

It seems clear that the existence of distinct isotypic determinants is due to specific conformational features of the constant region of the heavy chains of immunoglobulins. Unlike for some other protein systems, however, such as myoglobin (Atassi, 1975) and lysozyme (Atassi et al., 1976 Lee and Atassi, 1977a,b Atassi and Lee, 1978a,fo Atassi, 1978), the location of the various determinants has not been precisely mapped and correlated with particular structural features. 

Known sequences of the Fc segments of proteins representative of the various human IgG subclasses are displayed in Fig. 1. As emphasized previously, information regarding the precise location of specific heavy-chain determinants, be they class, subclass, or allotype specific, is regrettably sparse. They are to be found, however, in large measure, in the 

---

Antibodies can be separated into different classes (IgM, IgG, IgA, and IgE) and subclasses (IgGl, IgG2a, IgG2b, and so on) on the basis of the structure of their heavy chains. This can be achieved using antisera directed against epitopes on the heavy chains that are specific for the particular isotype. The different classes have different properties and this may be important in determining the usefulness of the antibodies for example in diagnostic and therapeutic apphcations. 

---