An epitope on Ki antigen recognized by autoantibodies from lupus patients shows homology with the sv40 large t antigen nuclear localization signal

Abstract

Objective. Epitopes on Ki antigen were analyzed using synthetic peptides, including KILT, a 16-mer peptide with an amino acid sequence homologous to the SV40 large T antigen nuclear localization signal (SV40 T NLS).Methods. In addition to KILT, 4 synthetic peptides, all potential epitopes on Ki antigen according to computer analysis, were prepared and tested for reactivity with 49 anti-Ki-positive lupus sera by enzymelinked immunosorbent assay.Results. Eighteen sera reacted with KILT, but not with other peptides. The reaction of anti-Ki sera with KILT was specifically inhibited by recombinant Ki antigen. Eight of 49 anti-Ki sera reacted with a 7-mer synthetic peptide of SV40 T NLS, and the reaction was specifically inhibited by KILT.Conclusion. The 16-mer Ki peptide containing the sequence homologous to the SV40 T NLS is one of the antigenic epitopes recognized by anti-Ki antibodies in lupus sera.

Clinical and serological features of 35 patients with anti-Ki autoantibodies

“…The occurrence of anti-Ki antibodies in different clinical conditions could be tentatively explained by the reactivity of these antibodies with different epitopes of the same antigen as suggested by previous studies. 7,8 The main clinical features recorded in our study, independently from the clinical diagnoses, were skin involvement and sicca symptoms. Even if both sicca and Ro/SSA antibodies were frequently recorded in our cohort of patients, no specific association was observed between these clinical and laboratory features.…”

“…5,6 Ki nuclear protein contains multiple epitopes recognized by different autoimmune sera 7 in particular, one epitope, mostly recognized by SLE sera, showed a sequence homologous to the SV40 large T antigen localization signal. 8 Different authors suggested a specific association with SLE, confirming a frequency of anti-Ki antibodies ranging from 6 to 20%, using double immunodiffusion (DID), counterimmunoelectrophoresis (CIE) or ELISA assays. 2,[9][10][11][12][13] However, anti-Ki were subsequently found in other autoimmune diseases such as systemic sclerosis, MCTD, vasculitides, 9,11 suggesting that this autoantibody should not be considered as a specific marker of lupus disease.…”

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

“…1,2,4,13,14 The incidence of anti-Ki antibodies in lupus sera was 6.7% by immunoprecipitation, 2 11.8% by DID, 1 18.9% by ELISA using recombinant Ki, 14 21.8% by ELISA using purified Ki, 4 and 16% by ELISA using KILT, 13 suggesting that the frequencies of anti-Ki antibodies depend on the immunoassay system. In our study, the immunoreactivity of anti-Ki sera (detected by DID) was tested by ELISA using KILT, purified Ki, or bNAX and by IB using purified Ki.…”

“…Based on these results, 160 µg/ml KILT, 5 µg/ml bNAX, and 5 µg/ml purified Ki were the antigen concentrations and 1 : 1000 was the serum dilution. 13 For the ELISA, antigen diluted in 0.05 M carbonatebicarbonate buffer (pH 8.5) was added to the wells of an immunoplate II (Nunc, Roskilde, Denmark) and incubated overnight at 4°C. After the coating solution was removed, the plate was washed three times with PBS-Tween.…”

“…The domain that is homologous to SV 40 T NLS was suggested to be highly antigenic, and it has been shown that this sequence is one of the epitopes on Ki antigen which can be recognized by autoantibodies in sera obtained from lupus patients. 13 Using a synthetic peptide that has homology with SV 40 T NLS, only 36.7% of anti-Ki sera (detected by double immunodiffusion, DID) reacted in an enzyme-linked immunosorbent assay (ELISA). The reported frequency of anti-Ki antibodies has varied between 6.7% and 21.4% using different immunoassays for detection.…”