Ligand-binding and idiotypic cross-reactions between anti-DNA antibodies and antibodies to Klebsiella K30 polysaccharide in patients with systemic lupus erythematosus or rheumatoid arthritis.

Antibodies to DNA and K30p were purified by affinity procedures and tested for their ability to cross-react with K30p and DNA, respectively. Anti-ssDNA antibodies were shown to react with solid-phase K30p and be inhibited in a dose-dependent manner by soluble ssDNA and K30p. Conversely, anti-K30p antibodies were found to bind immobilized ssDNA and be inhibited with soluble inhibitor. These results show that certain subpopulations of anti-ssDNA and anti-K30p antibodies overlap in their ligand-binding specificities. Idiotypic (Id) analysis showed that anti-K30p antibodies did not react significantly with an anti-Id reagent directed against a common anti-DNA framework Id (AM Id), thus clearly separating K30p-binding anti-DNA antibodies into an AM Id-negative population. When anti-DNA antibodies were probed with an anti-Id reagent directed against a framework Id present on anti-K30p antibodies (SP Id), substantial reactivity was found. Thus the SP Id identifies a subpopulation of antibodies capable of binding both K30p and DNA. These results show that a subset of anti-ssDNA antibodies cross-react with K30p antigen and are idiotypically related to a subset of antibodies reactive with K30p.