Idiotypic determinants on monoclonal autoantibodies to the Thy-1 antigen

Distinct monoclonal autoantibodies directed against the Thy-1 antigen differ in their reactivity with various target cells. The aim of the present study was to analyse the idiotypic specificities present on various monoclonal autoreactive Thy-1 antibodies. Xenogeneic anti-idiotypic (anti-Id) reagents were prepared by immunizing rabbits either with the 20-10-5 or with the C16-31 monoclonal Thy-1 autoantibodies. Both of the anti-Id reagents reacted with the immunizing MoAb in ELISA and inhibited the interaction of the immunizing MoAb with Thy-1-positive target cells. The anti-20-10-5 reagent reacted in ELISA inhibition tests with the C16-31 MoAb, yet failed to inhibit the binding of C16-31 MoAb to thymocytes. Anti-C16-31 Id reacted with the 20-10-5 MoAb both in ELISA assays and in cell-bound fluorescence inhibition tests. These results indicate that anti-C16-31 Id detects an Id determinant shared by C16-31 and 20-10-5 MoAb, which is a binding site-related idiotype, while anti-20-10-5 Id detects an idiotypic determinant shared by these two MoAb that is not located at the combining site of C16-31 MoAb. In contrast to the marked cross-reactivity found between C16-31 and 20-10-5 MoAb, the two anti-Id reagents showed only a weak cross-reactivity with five other Thy-1 autoantibodies tested, including those autoantibodies that showed patterns of reactivity similar to those of C16-31 and 20-10-5, with various target cells. It is concluded, therefore, that individual autoreactive Thy-1 MoAb possess distinctive idiotypic determinants, although some cross-reactivity can be detected between certain MoAbs.