Anti-ribosomal antibodies from lupus patients bind DNA

Abstract

Antibodies specific for ribosomal P proteins (anti-P) are a hallmark of systemic lupus as anti-DNA antibodies are. It has been reported that anti-P antibodies are more frequently detected in anti-dsDNA positive sera. The aim of the present study was to verify the binding ability of anti-P antibodies towards polynucleotides and nucleosomes. We purified anti-P antibodies from 8 SLE patients' sera and we analysed them by ELISA on plates coated with DNA or nucleosomes. We performed also inhibition experiments in order to verify the specificity of the binding. All the purified anti-P antibodies bound DNA, but some anti-DNA binding activity remained among the non-anti-P antibodies in the flow through. Only half of the purified antibodies bound to nucleosomes, and anti-nucleosomal activity was demonstrated also in non anti-P antibody fraction. The inhibition experiments performed on two anti-P antibodies pointed out that only the homologous antigen inhibited the binding to either P peptide or DNA coated onto the solid phase. These results show that sera in which the two specificities coexist contain antibodies endowed with a double binding ability for DNA and the P peptide.

Fig. 1

Binding of purified anti-P antibodies (•) and of the flow throughs (○) to ssDNA coated plate in ELISA. Purified anti-P antibodies were tested at concentration of 20, 10, 5 and 2·5 µg/ml. Antibodies of the flow throughs were tested at concentration of 20, 10 and 5 µg/ml.

Fig. 2

Binding of purified anti-P antibodies (▪) and of the flow throughs (□) to dsDNA coated plate in ELISA. Purified anti-P antibodies were tested at concentration of 20, 10, 5 and 2·5 µg/ml. Antibodies of the flow throughs were tested at concentration of 20, 10 and 5 µg/ml.

Fig. 3

Purified anti-P antibodies from Pt 7 were preincubated with various inhibitory agents at concentrations between 100 and 0·05 µg/ml, then dispensed to (a) ribosomal MAP or (b) DNA coated plate in order to verify the residual binding activity. See Materials and methods for details. • Ribosomal MAP, □ MAP LKM, □ dsDNA, ▴ polydGdC, ○ ssDNA, ▵ polyApolyU.

Fig. 4

Purified anti-P antibodies from Pt 3 were preincubated with various inhibitory agents at concentrations between 100 and 0·05 µg/ml, then dispensed to ribosomal MAP or DNA coated plate in order to verify the residual binding activity. See Materials and methods for details. • Ribosomal MAP, ▪ MAP LKM, □ dsDNA, ▴ polydGdC, ○ ssDNA, ▵ polyApolyU.