The concepts of crossreactivity and specificity in immunology

The advent of direct binding assays for studying the interactions of immunoglobulins and antigens has made it important to distinguish among several types of crossreactivity. The molecular basis of crossreactivity is reviewed and the behavior of these different processes in the displacement curves ordinarily used for radioimmunoassay is analysed in detail. Both the structure of the antigens and the homogeneity or heterogeneity of the antibodies must be explicitly considered. Immunological specificity may be defined by similar reasoning. These concepts, which represent applications of the principles of protein chemistry, should also be useful in describing the interactions of molecules in solution with cell receptors.