[Clinical evaluation of quantitative measurement of various antinuclear antibodies by enzyme immunoassay].

Quantitative analysis of several antinuclear antibodies (ANAs) by enzyme immunoassay (EIA) has been developed and widely used. Among them, the EIA coating fragmented HEp-2 cells nuclei is a new approach for quantitating the amount of total ANAs. The EIA to detect IgG anti double-stranded DNA antibodies (dsDNA-EIA) is a highly sensitive method, but less sensitive compared with radioimmunoassay (Farr's assay) which detects anti dsDNA antibodies of total immunoglobulins. EIA to quantitate IgG anti single-stranded DNA antibodies (ssDNA-EIA) has been simultaneously used with dsDNA-EIA in our country. However, ssDNA-EIA detects not only anti ssDNA antibodies against purine and pyrimidine bases, but it also detects anti dsDNA antibodies which react with the phosphate-ribose backbones or internal duplex structures in the ssDNA antigen. Thus only the use of dsDNA-EIA is recommended for clinical purpose. EIAs coating RNP, Sm, SS-A/Ro and SS-B/La autoantigens using recombinant and/or purified natural antigens were useful to quantitate autoantibodies. However, some sera containing antibodies to RNP or SS-A/Ro, did not react with recombinant antigens because of the lack of C-peptide protein of RNP or conformational structures. The positive level of each EIA should be reevaluated in comparison with the results obtained from the double immunodiffusion and disease distribution of each antibody previously reported.