Sensitivity of the HEp-2000 substrate for the detection of Anti-SSA/Ro60 antibodies

Anti-SSA/Ro antibodies are the most prevalent type of antinuclear antibody (ANA). Anti-SSA/Re-positive sera may recognise two proteins: a 52 kDa (Ro52 ) and a 60 kDa (Ro60) subunit. We studied the sensitivity for Ro60 detectio n using the HEp-2000 substrate, which consists of HEp-2 cells transfected w ith Ro60 cDNA in an anti-SSA/Ro-positive population consecutively identifie d by double immunodiffusion (DID) with thymus/spleen nuclear extract and li ne immunoassay (LIA) with recombinant Ro52 and Ro60. One hundred and twenty -seven consecutive anti-SSA/Re-positive sera defined by DID with thymus/spl een nuclear extract and LIA using recombinant Ro52 and Ro60 were analysed o n HEp-2000 and DID with natural Ro60. Of these, 91 were anti-Ro60 positive on LIA and/or DID with natural Ro60. The HEp-2000 substrate detected 70/91 (sensitivity 77%) and correlated strongest with DID. Most of the missed ant i-Ro60-positive sera had high ANA intensity. The substrate did not detect m onospecific anti-Ro52 antibodies (sensitivity 9.7%; 3/31), HEp-2000 substra te can therefore be considered a reliable, simple and alternative method fo r DID in the detection of anti-Ro60 reactivity. Special follow-up should be given to sera with strong ANA patterns in which the SSA/Ro60 staining patt ern may be hidden.