[Enzyme-immunoassay using recombinant antigen]

Since Hargraves et al reported the LE cells in 1948, many antinuclear antibodies (ANAs) have been classified using various immunological methods, and have become an important tool for the diagnosis of various connective tissue diseases. Although the enzyme-immunoassay (EIA) is known as a safe and sensitive quantitative-method to detect ANAs, it has not been used routinely because of difficulty to prepare a large amount of antigens reactive with autoantibodies specifically. Many investigators have established EIA systems using recombinant proteins to overcome this problem and some of them have been useful for the diagnosis of connective tissue diseases showing highly specific and sensitive reactions to autoantibodies. However, some sera positive for autoantibodies to several nuclear antigens such as U1 RNP, Sm and SS-A, do not react with the recombinant proteins because those autoantibodies often recognize the conformational profiles of the autoantigens. Although many problems still remain to be solved, EIA using recombinant protein is superior as a quantitative method than other methods such as double immunodiffusion (DID), and it can provide much more useful information to estimate the effect of treatment. Therefore, at this moment, the use of both DID and EIA is recommended to diagnose the patients and to evaluate the disease activities, and may clarify the clinical significance of EIA using recombinant antigens.