We established a sandwich radioimmunoassay using two monoclonal antibodies specific for the distinct allotypic determinants on heavy and light chains of antigen-specific suppressor T cell factors (TsF). By use of this assay system, we confirmed our previous findings that the allotypic determinants (Ct) detected by BALB/c anti-CB-20 (7C5 and 7D1) were shared in various TsF with different antigen specificities, and also that the genes coding for the Ct determinants were indicated to be located on the right side of the Igh-V gene cluster, because the assay system equally detected either KLH-TsF or OVA-TsF from Ighb mice, such as C57BL/6, CB-20 and BAB-14, but not from BALB/c or C3H with other Igh allotypes. Furthermore, the radioimmunoassay, when used with two different anti-Ct (7C5 and 7D1), preferentially detected the extracted form of TsF, whereas the secreted TsF was easily detected by the combination of anti-Ct (7D1) and anti-I-Jb. In fact, the assay system defined two types of Ts hybridomas: one producing TsF in cytoplasm or on the membrane but not secreting and another secreting in the culture supernates. We also demonstrated that materials bound to the plate coated with anti-Ct antibody that had been incubated with different concentrations of cell-free extracts exhibited the dose-dependent suppression of antibody responses.
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