Detection of NIMA^d-specific T_R cells using a DTH bystander suppression assay. Splenocytes were collected from NIMA^d-exposed and NIPA^d control offspring immunized with tetanus toxoid and diphtheria (TT/DT) vaccine 2 weeks previously. A total of 10 million splenocytes were injected into footpads of naive B6 recipients with coinjection inoculums: PBS, BDF₁, or B6C3F₁ Ag, or TT/DT. To measure bystander suppression, splenocytes were coinjected with BDF₁Ag and TT/DT. Changes in footpad thickness were measured after 24 hours of injection to measure DTH reaction. (A) Examples of DTH bystander suppression assays. Spleen cells from 2 NIMA^d-exposed mice (nos. 7 and 8) and 1 NIPA^d control mouse (no. 1) that had been immunized with TT were coinjected into footpads with antigens shown on x-axis. Splenocytes from NIMA^d no. 7 had a strong DTH response to TT but not to BDF₁ antigen; the TT response was suppressed by 50% in the presence of BDF₁ (maternal) Ag, but not in presence of third-party (B6C3F₁) Ag. NIMA^d no. 8 and the NIPA^d control (no. 1) splenocytes did not suppress their strong anti-TT DTH responses in presence of the BDF₁ Ag. (B) Summary of bystander suppression values in n = 54 mice. The horizontal lines represent mean values.