A primary in Vitro antibody assay for antigen-specific T-suppressor factor: Cross-suppression of TNP-specific antibody responses by TMA-specific TsF 1

Abstract

We have previously shown that phenyltrimethylammonium (TMA)-specific, first-order suppressor T cells (Ts 1) and soluble factors extracted from these cells (TsF 1) can suppress delayedtype hypersensitivity (DTH) responses. The TsF 1, as monitored in the DTH system, was characterized and found to be a single-chain, antigen-binding, I-J +, and Id + molecule. To monitor TsF 1 in an efficient manner, an in vitro antibody system was developed. The studies show that in vitro stimulation of naive A/J spleen cells with the thymic-independent antigen, Brucella abortus, to which TMA and trinitrophenol (TNP) or fluorescein (FL) are coupled (TMA-BA-TNP or TMA-BA-FL), induces significant numbers of anti-TNP or anti-FL plaque-forming cell (PFC) responses. The addition of TMA-specific TsF 1 results in the cross-suppression of 30–50% of the total anti-TNP and FL PFC responses. This activity is antigen (TMA) dependent since suppression occurs only when the TMA ligand is present in the culture media. Analysis of the TNP-specific PFC responses in nonsuppressed cultures revealed that 20–35% of the PFC bear the cross-reactive idiotype(s) (CRI) normally associated with anti-TMA antibodies. In cultures containing TMA-TsF 1, CRI +PFC are suppressed by 90–100% while the CRI −PFC are suppressed only by 10–30%. Our studies further show that an induction-phase, antigen-binding, CRI +, and I-J + single-chain factor is responsible for the observed in vitro suppression. The possibility of utilizing this assay to monitor a variety of antigen-specific suppressor factors is discussed.