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ANTI‐IDIOTYPIC IMMUNITY AND AUTOIMMUNITY III. INVESTIGATIONS BY ELISA METHODS

We have recently shown that autoantibodies to thyroglobulin (Tg) from rats with spontaneous autoimmune thyroiditis share idiotypic determinants and can be characterized using heterologous anti-idiotypic antibodies1 Similar studies, using sera from patients with autoimmune thyroiditis and rats with mercuric chloride-induced glomerulonephritis, are ongoing in our laboratory. Several types of enzyme-linked irnmunosorbent assays (ELISA) are being used in each of these studies, including those for the detection of circulating autoantibodies and those for the evaluation of experimentally induced anti-idiotypic antibodies. Our experiments using thyroiditis sera indicate that ELISA detects titers of anti-Tg antibodies very similar to those detected by a more traditional coprecipitation radioimmunoassay (RIA). Simultaneous titration of a pool of human thyroiditis sera by the two methods produced similar titration curves, each detecting antibody activity in dilutions of the serum pool up to 1 : lO; . In experimental glomerulonephritis, ELISA has proven more sensitive, in our laboratory, than immunofluorescence for the detection of antiglomerular basement membrane (GBM) antibodies.2 Indirect immunofluorescence titers of anti-GBM antibodies in this model rarely exceed 20 and are detectable in only 45% of the treated rats. By ELISA, 100% of the treated rats surveyed had detectable levels of anti-GBM, with titers as high as lo3. Heterologous anti-idiotypic antibodies have been developed for the disease models described above. ELISA techniques were used to monitor the reactivity of the anti-idiotypic antibodies against the idiotypes and normal immunoglobulins. In both the human and the rat systems, ELISA demonstrated residual activity specific for the idiotype after exhaustive absorption of the anti-idiotypes with normal immunoglobulins. In the human model, RIA were run with 1231labeled idiotype and labeled normal immunoglobulin, which confirmed the ELISA results. The ELISA techniques used in the assessment of these antiidiotypic antibodies equalled or surpassed the sensitivities of RIA used for the same purpose, but proved to be quicker, easier, and safer to perform. Current data have indicated the feasibility of using inhibition assays in ELISA methods. In the model systems described above for the detection of circulating autoantibodies, preincubation of the autoantiserum with homologous antigen has been shown to be capable of inhibiting the ELISA reaction. In addition, crossreactive heterologous antigens were capable of partially inhibiting the ELISA reactivity of autoantibodies. It may be possible to use similar inhibition-type assays to determine if anti-idiotypic antibodies are binding site specific; we are currently exploring this possibility in our laboratory.