Recent advances in molecular biology have permitted significant progress in correlating the chemical structure and biological function of naturally occurring macromolecules. The problem of the nature and mechanism of the immune response is a field of molecular biology which still poses many difficulties at both the cellular and the molecular level. The heterogeneity of antibodies is an outstanding example of these difficulties. One of the approaches to a better understanding of the chemical basis of immunological phenomena was the use of simple and well-defined molecules as elicitors of the various types of immune response. The use of synthetic polypeptides, polypeptidyl proteins, and of conjugates of various small molecules with synthetic polypeptides in studies of the molecular basis of immunological phenomena (for review, see Sela 1966) facilitates, due to the relative simplicity of these antigenic models, the interpretation of results obtained with them and sometimes permits the detection of differences, such as genetic variations in the capacity to produce specific antibodies (Levine, Ojeda & Benacerraf 1963; McDevitt & Sela 1965), which are not observable with complex natural antigens. Antibodies directed toward synthetic polypeptides may prove useful in studies of the antibody structure and biosynthesis, as it should be possible to correlate differences between the antibodies with the known differences between the synthetic antigens.
