Crossed immunoelectrophoresis: Qualitative and quantitative considerations

Invented 20 years ago, crossed immunoelectrophoresis (X-IEP) today is a technique of unusual power and myriad application. It combines very high resolution with exquisite specificity by alloying 2-dimensional electrophoresis with immunoprecipitation for symbiotic new potentialities. The consequent matchless quantitative/qualitative capabilities of X-IEP for analyzing antigens in complex mixtures, particularly by their idiomatic internal comparisons, are still not widely recognized. Because of this and the supposed complications of its use and interpretation, X-IEP is more rarely used than it should be. This essay discusses contemporary X-IEP with the particular aims of demonstrating that it is not difficult to use and of explaining with selected examples why it is peculiarly powerful for analyzing antigen mixtures like the body fluids, tissue and cell extracts, and microbial homogenates.