Autoantibodies to lens epithelium-derived growth factor/transcription co-activator P75 (LEDGF/P75) in children with chronic nonspecific complaints and with positive antinuclear antibodies

Autoimmune fatigue syndrome (AIFS) is characterized by chronic nonspecific complaints, consistently positive antinuclear antibodies (ANA), and lack of alternate medical explanations. A newly recognized antibody, named anti-Sa, was detected in approximately 40% of the patients by Western blot (WB) using HeLa extract. Some patients with AIFS later develop chronic fatigue syndrome (CFS), and most of them are positive for anti-Sa. On the other hand, Muro et al. reported anti-DFS70 in patients with CFS. Anti-Sa and anti-DFS70 were turned out to be same specificities by exchanging studies of blind sera. The target antigen of anti-DFS70 was identified as lens epithelium derived growth factor/transcription co-activator p75 (LEDGF/p75). The objectives of this study are to confirm whether the target antigen of anti-Sa is also LEDGF/p75, and to develop ELISA system by using recombinant protein. Recombinant protein of LEDGF/p75 was purchased from Protein One (Bethesda, MD, USA). We developed an ELISA system to detect anti-LEDGF/p75 by coating this recombinant protein. 226 sera of AIFS patients (including 36 CFS patients) were applied to this ELISA assay and Western immunoblot, and it was revealed that anti-Sa-positive sera defined by WB and sera positive for anti-LEDGF/p75 on ELISA were identical. Moreover, reactivities of anti-Sa on WB were inhibited by pre-incubating with recombinant LEDGF/p75, and eluted antibodies from the nitrocellulose membrane could react on the ELISA. These results confirm that the Sa antigen is LEDGF/p75. The ELISA assay using recombinant LEDGF/p75 could be a promising tool for measuring anti-Sa and consequently for diagnosing CFS.