Cross-reactions of human lupus autoantibodies with 8-methoxypsoralen photomodified DNA fragments

SLE autoantibodies binding to native calf thymus DNA brominated in high salt

Native calf thymus DNA was brominated in high salt to achieve B-->Z conformational transition. Ultraviolet and circular dichroism spectroscopic studies point towards the conformational modification of the native DNA. Specific binding of the monoclonal anti-Z-DNA antibody (Z-22) to the DNA brominated in high salt further confirmed the B-->Z conformational isomerization of native DNA. The role of Z-DNA in the etiopathogenesis of systemic lupus erythematosus has been investigated in the light of the binding of naturally occurring human anti-DNA autoantibodies to the induced Z-DNA.

Native DNA fragments photocrosslinked to psoralen binds to anti-B and anti-Z DNA antibodies

Calf thymus DNA fragments of varying size (100-600 bp) were covalently linked to psoralen in the presence of 365 nm UV light. The crosslinked species were separated from the monoadducts by hydroxyapatite column chromatography. The DNA-psoralen crosslink showed binding with naturally occurring anti-DNA autoantibodies. This was substantiated by the recognition of affinity purified IgG by DNA-psoralen crosslinks of varying DNA size. The photo-crosslinks exhibited considerable recognition of both monoclonal and polyclonal anti-Z-DNA antibodies in inhibition ELISA and band shift assay.

Preferential recognition of specific DNA motifs by anti-double-stranded DNA autoantibodies

Although antibodies (Ab) specific for double-stranded (ds) DNA are thought to be involved in the etiopathogenesis of systemic lupus erythematosus (SLE), the fine structure of their DNA targets remains elusive. We have adapted a polymerase chain reaction (PCR)-assisted immunoprecipitation method to define the binding sites in DNA sequences recognized by high affinity anti-dsDNA Ab of SLE patients. SLE sera were used to bind templates from a pool of double-stranded oligonucleotides (ON). A central part of 20 base-pair random sequence was flanked by restriction endonuclease recognition sites and sequences complementary to predefined PCR primers. Immunoselected ON were precipitated, isolated from the immune complexes and then subjected to a further immunoprecipitation step after amplification by PCR. After five cycles of immunoprecipitation and PCR, the resulting ON were cloned. Sequence analysis revealed that sera from SLE patients and two human monoclonal anti-dsDNA Ab obtained from SLE patients preferentially select sequences expected to form non-B-DNA structures. Inhibition studies of the Farr assay confirmed the increased affinity of the selected epitopes for anti-DNA Ab as compared to random B-DNA.