OBJECTIVETo develop an improved substrate for indirect immunofluorescence test (IIF) for detecting anti-Ro60/Sjogren's syndrome A (Ro/SSA) autoantibodies.

METHODS60-kDa Ro/SSA autoantigens (Ro60) cDNAs were obtained from human placental cDNA library using polymerase chain reaction (PCR) and were cloned into the mammalian expression vector-pEGFP-C1. Then, the recombinant plasmids were transfected into HEp-2 cells. We confirmed the overexpression, localization and antigenicity of fusion proteins in transfected cells by means of immunoblotting, confocal fluorescence microscopy and IIF. HEp-2 and HEp-Ro60 were analyzed by IIF using a panel of 10 precipitin-positive anti-Ro human sera simultaneously.

RESULTSStable expression of Ro60-green fluorescent protein (Ro60-GFP) fusion proteins were maintained ten more generations. Ro60-GFP kept the antigenicity of Ro while demonstrating its own characteristic immunofluorescent pattern in HEp-Ro60 cells. The transfectants dramatically increased the sensitivity of IIF testing (a mean increase of 6.7-fold in endpoint titer). Eight over ten (8/10) positive anti-Ro sera showed characteristic immunofluorescent patterns for HEp-Ro60, including two sera that were anti-nuclear antibodies (ANA) negative for untransfected HEp-2. IIF-ANA in all healthy sera was negative for HEp-Ro60.

CONCLUSIONSAs a new substrate for IIF, the Ro60 transfectants can be used to detect anti-Ro antibodies. In addition, transfected HEp-2 cells keep the immunofluorescent properties of HEp-2 cells in IIF-ANA tests and can be employed as a substrate for routine IIF-ANA detection.