1392 CHARACTERIZATION OF TsF 2 SUPPRESSOR

The sequential interactions between T lymphocyte subsets have been well characterized in several systems of antigen-specific immune suppression (1-2). The immune response to the hapten 4-hydroxy-3-nitrophenyl acetyl (NP) a has become one of the most extensively characterized of these model systems (3-6). Previous studies from our laboratory have revealed that in this suppressor network system, at least three distinct sets of T cells are required for suppression. The first set of suppressor T cells, termed TSl, are induced by antigen, bear an idiotypic receptor, and function early in the immune response. These TSl induce a second set of suppressor T cells, termed Ts2 (3, 7). The Ts2 bear anti-idiotypic receptors and function late in the immune response (3-5). Furthermore, the Ts2 populat ion or a soluble factor derived from these cells activates an ant igen-primed Ts3 populat ion that is thought to mediate the additional suppressor signals (4). Most studies, including these in the NP system, appear to be f ragmentary in that the entire sequence of cell interactions has not been fully defined. A serious limitation of these studies has been the lack of suppressor cell clones or hybr idomas to further characterize the different suppressor cell populat ions and the molecules responsible for the communica t ion between these cells. For a better unders tanding of the precise nature and function of each part icipating suppressor T cell subset, we have recently prepared a series of monoclonal T cell hybr idomas that are specific for NP (7-8). We previously (7, 8) characterized these hybrids and demonstrated that they correspond to the Tsl population. We now characterize another group of T cell hybrids that corresponds to the Tsg population. Furthermore, we characterize the biologically active suppressor factor (TsF2) produced by these cells and compare it with the TsF1 factor obtained from the Tsl hybrids.