Two immunoassays have been used to detect autoantibodies to the ribosomal P proteins (Rib-P) which are a serologic marker for systemic lupus erythematosus (SLE).

Enzyme immunoassays and an indirect immunofluorescence test have been tested and compared in their ability to diagnose SLE and to see whether the results are interrelated.

Scientists at Dong-A University College of Medicine (Busan, Republic of Korea) collected serum samples from 91 SLE patients, 50 rheumatoid arthritis patients and 43 healthy subjects, between March 2009 and May 2010. A total of 184 samples were analyzed for anti-Rib-P antibodies using two immunoassays and an indirect immunofluorescence test (IIF) simultaneously. The IIF on HEp-2 cells was assayed using HEP-ANA test system (Medical & Biological Laboratories, MBL, Naka-ku, Japan) and anti-Rib-P antibodies by IIF were determined by the pattern with cytoplasmic and nucleolar staining.

Of 91 SLE patients, the positive rates of two immunoassays for anti-Rib-P antibodies were significantly higher than that of IIF. Eleven of 91 SLE patients showed simultaneous positivity in two immunoassays, but negativity in IIF. None of 93 control group subjects was positive for anti-Rib-P antibodies in two immunoassays and IIF. The two immunoassays used were the Quanta Lite Ribosome P enzyme-linked immunosorbent assay (ELISA) (Inova Diagnostics, San Diego, CA, USA) which uses synthetic ribosome P antigen and the EliA Rib-P (Phadia AB; Uppsala, Sweden) which uses human recombinant ribosomal P-proteins P0, P1, and P2.

The authors concluded that the sensitivity of immunofluorescence antibody tests (IFA) on HEp-2 cells is not optimal as a first-line screening test for detection of anti-Rib-P in SLE patients. Therefore, additional immunoassays are required to determine the presence of anti-Rib-P antibodies. The high titer of anti-Rib-P antibodies determined using immunoassays could also be demonstrated by IIF on HEp-2 cells. The discrepancy between immunoassays and IIF on HEp-2 cells for detection of anti-Rib-P antibodies may be explained by their titer. The study was published on March 15, 2012, in the journal Clinica Chimica Acta.

Related Links:
Dong-A University College of Medicine
Medical & Biological Laboratories
Inova Diagnostics