title: Detection of masked anti-DNA antibodies in lupus sera by a monoclonal anti-idiotype.
abstract: We report here the use of a monoclonal anti-idiotype 3I to human anti-DNA antibodies to detect in serum idiotype-positive antigen-binding antibodies lacking DNA-binding activity as measured by conventional antigen binding assays. We studied paired serum samples from 13 patients with systemic lupus obtained at two times in the course of their disease: in each patient, one serum sample has anti-DNA activity and the second serum sample has no anti-dsDNA activity detectable by Millipore filter, ELISA, or Crithidia assay. Reactivity with 3I as detected with a radioimmunoassay (RIA) was present in all 13 sera with anti-dsDNA activity. Six patients showed a decrease in 3I reactivity to normal levels in the second serum sample, in which anti-dsDNA antibodies were not detectable by conventional antigen-binding assays. The other seven patients' second serum sample continued to show elevated 3I reactivity by RIA even though no anti-dsDNA activity was apparent. When the 3I-reactive antibodies from these latter patients' sera were eluted from a 3I affinity column, they revealed DNA-binding activity. Furthermore, dsDNA binding by these sera was apparent when they were displayed on Western blots of isoelectric focusing gels run in 8 M urea and incubated with radiolabeled dsDNA. These results indicate that the 3I anti-idiotype can detect anti-DNA antibodies in some sera of SLE patients that lack anti-DNA activity by ordinary assays. These antibodies may be inhibited in binding dsDNA by excess antigen or autologous anti-idiotype, and their DNA binding activity can be unmasked by procedures promoting immune complex dissociation.
mesh_terms: D000888:Antibodies, Anti-Idiotypic; D000974:Antibodies, Antinuclear / Q000032:analysis* / Q000276:immunology; D000911:Antibodies, Monoclonal; D001666:Binding Sites, Antibody; D003101:Collodion; D004247:DNA / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007130:Immunoglobulin Idiotypes / Q000276:immunology*; D007525:Isoelectric Focusing; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D010209:Paper
chemical_list: D000888:Antibodies, Anti-Idiotypic; D000974:Antibodies, Antinuclear; D000911:Antibodies, Monoclonal; D007130:Immunoglobulin Idiotypes; D003101:Collodion; D004247:DNA