Anti-Ki antibodies recognize an epitope homologous with SV40 nuclear localization signal: clinical significance and reactivities in various immunoassays

Abstract

We studied the characteristics of anti-Ki antibodies that react with a synthetic peptide (KILT) which has homology with SV40 large T antigen nuclear localization signal (SV40 T NLS). Immunoreactivity of antibodies to KILT was tested by enzyme-linked immunosorbent assay (ELISA), and this reactivity was compared with results obtained by immunoblotting using purified Ki and ELISA using purified or recombinant Ki antigen. The clinical significance of anti-KILT antibodies in lupus patients was also studied. Twenty percent of anti-Ki sera reacted with KILT, and all sera that reacted with KILT recognized both purified and recombinant Ki antigen in all our assay systems. A significant correlation was observed between reactivities in ELISA using KILT and with these using purified and recombinant Ki. Some sera with low titers by double immunodiffusion (DID) reacted with KILT, whereas high-titer anti-Ki sera showed a tendency to react with Ki antigen in different assays. The prevalence of discoid rash and sicca complex was higher in the anti-KILT-positive group. The amino acid sequence homologous to SV40 T NLS is an immunologically active epitope on the Ki antigen; reactivity to this epitope is associated with characteristic clinical features allied with anti-Ki antibodies in lupus patients.

Key words::

• Anti-Ki antibody
• Ki antigen
• SV40 large T antigen
• Systemic lupus erythematosus (SLE)