Expression, localization, and clinical application of the RNA binding domain of U1-70kD in HEp-2 cells.

Objective. To develop an improved substrate for indirect immunofluorescent test (IIF) to detect anti-U1-70kD autoantibodies. Methods. The RNA binding domain of U1-70kD (U1BD) complementary DNA was obtained from human larynx carcinoma cell line HEp-2 by reverse transcription-polymerase chain reaction (RT-PCR) and cloned into the mammalian expression vector pEGFP-C1. The recombinant plasmid pEGFP-U1BD was transfected into HEp-2 cells. Immunoblotting (IBT), confocal fluorescence microscopy, and IIF were used to confirm the expression, localization, and antigenicity of fusion proteins of green fluorescent protein (GFP) in transfected HEp-2 cells, which were then analyzed by IIF using human reference sera and compared with untransfected HEp-2 cells simultaneously. Results. (1) The HEp-U1BD cells thus obtained retained their ability to express U1BD-GFP, which showed the antigenicity of U1BD with a characteristic phenotype in IIF. (2) Fifteen IBT-positive anti-U1-70kD sera presented with characteristic cytoplasmic staining on HEp-U1BD by IIF, but five sera without the 70kD reactive band in IBT were not found in the presence of HEp-U1BD pattern. Ten sera of healthy donors couldn't react with HEp-2 and HEp-U1BD at 1: 80 attenuant degrees. (3) No differences in expression, localization, or morphology were observed when HEp-U1BD or HEp-2 interacted with the reference sera that could react with Ro/SSA, La/SSB, centromere, histone, and Scl-70 antigens in routine IIF test. Conclusions. HEp-U1BD cells kept the immunofluorescent properties of HEp-2 cells in an immunofluorescence anti-nuclear antibody (IFANA) test and could be potentially used as a substrate for routine IFANA detection.