No abstract

Among the many complex lymphocyte interactions, the mechanisms of immune suppression are among the most intensively investigated. Several laboratories have shown that T cell-mediated suppression involves the interaction of at least two distinct subsets of T lymphocytes (1-5). We recently described the characteristics of two T cell subpopulations mediating suppression of delayed-type hypersensitivity (DTH)1 to the haptenic determinant 4-hydroxy-3-nitrophenyl (NP) (6, 7). When mice were injected with NP-derivatized syngeneic spleen cells, suppressive activity could be transferred to syngeneic recipients either before immunization with the NP compound, termed induction-phase suppression, or immediately before challenge for a DTH response, termed effector-phase suppression. Whereas the fine specificity of the induction-phase suppressor of Igh-lb-bearing mice was heteroclitic (cross-reactive with 4-hydroxy,5-iodo-3-nitrophenyl acetyl hapten [NIP]),just as the serum antibody, the fine specificity of the effector suppressors was not heteroclitic. Treatment of suppressor cell populations with anti-idiotype plus complement could abrogate induction-phase suppressor transfer without interfering with effector-phase suppressor transfer. Thus, it was concluded that these two modes of suppression were essentially assays of distinct suppressor T cell subsets. It was also shown that effector-suppressor transfer is restricted by Igh-V and -I region genes (7). To provide a more complete understanding of the mechanisms of immune suppression and to determine the significance of these genetic restrictions on the immune suppression pathway, the specificity of these two cell populations was investigated using direct antigen-binding methods. We have established that the NP idiotype-positive induction-phase suppressor T cells (Ts i) are in fact antigen binding, whereas the Npb-negative effector-phase suppressor T cell population (Ts ~) is anti-idiotypic. Furthermore, we provide evidence that the Ts i cell population induces the Ts" population.

Regulation of the immune response to antigen involves the interactions of many cell types. There is substantial evidence attesting to the decisive role of suppressor T cells in the inhibition of both humoral (1) and cell-mediated (2) immune reactivity to a variety of antigens. In addition, regulatory molecules derived from such suppressor T cells have been identified in a number of experimental systems (reviewed in 3, 4).Suppressor T cells (Ts) 1 operative in regulating responses to many antigens have been shown to express certain Lyt differentiation markers, as well as structures encoded by the I subregion of the H-2 major histocompatibility complex (MHC) (5). Furthermore, antigen-specific Ts-derived suppressor factors (TsF) have been found in many different systems to bear determinants encoded by the I-J subregions of the H-2 MHC (3, 4). Despite the above mentioned information, the mechanisms by which Ts and TsF exert their inhibitory effect is complex and not completely understood. Moreover, the precise number of phenotypically distinct Ts and TsF has not been determined. As a result, it has not been possible to formulate a single, all encompassing scheme which can explain related data from many different laboratories, each employing distinct experimental systems.In an attempt to elucidate the role of antigen-specific Ts and their factor(s) in the regulation of cell-mediated immune response, over the past 3 y, our laboratory has been studying delayed-type hypersensitivity (DTH) to the p-azobenzenearsonate (ABA) hapten (6-8). Conjugates of this hapten evoke an anti-ABA antibody response in certain strains of mice, in which the antibody molecules bear cross-reactive idiotypic (CRI) structures and can be detected by anti-idiotypic antiserum.* Supported by National Institutes of Health grants AI-16396-01 and AI-14732, and by the Cancer Research Institute, Inc., New York.l Abbreviations used in this paper: ABA, p-azobenzenearsonate; ABA-BSA, p-azobenzenearsonate-conjugated bovine serum albumin; ABA-SC, p-azobenzenearsonate-coupled syngeneic spleen cells; anti-CRI, anticross-reactive idiotypic antibodies; CRI, cross-reactive idiotype common to anti-ABA antibodies of A/J mice; DTH, delayed-type hypersensitivity; GAT, L-glutamic acidn°-L-alaninea°-t.-tyrosinel°; GT, L-glutamic acid~°-L-tyrosineS°; HBSS, Hanks' balanced salt solution; IBC, idiotype-binding capacity; MHC, major histocompatibility complex; NMS, normal mouse serum; NRS, normal rabbit serum; PBS, phosphatebuffered saline; PBS-5, phosphate-buffered saline containing 5% fetal calf serum; RAMIg, rabbit antimouse immunoglobulin; TNP, trinitrophenol; TS, suppressor T cells; Ts~, suppressor T cells induced by antigen; TsF, suppressor T cell factors derived from Tsl; Ts2, suppressor T cells induced by TsF; Vn, variable portion of the Ig heavy chain. J. Exp. M Et~.

A combination of in vitro and in vivo techniques were used to explore the mode of action of both crude and purified suppressive extracts specific for the random copolymer L-giutamic acid(60)-L-alanine(30)-L-tyrosine(10) (GAT- T(s)F) obtained from nonresponder DBA/1 (H-2(q)) mice. Normal DBA/1 spleen cells were incubated under modified Mishell-Dutton culture conditions for 2 days together with crude or purified GAT-T(s)F, and in the presence or absence of free GAT. These cells were then washed extensively and 3 × 10(6) viable cells transferred to syngeneic recipients, which were challenged at the same time with the immunogenic form of GAT complexed to methylated bovine serum albumin (GAT-MBSA). GAT-specific IgG plaque-forming cells (PFC) in the spleen were assayed 7 days later. In agreement with earlier in vitro studies on the action of GAT-T(s)F, it was demonstrated that under these conditions, low concentrations of GAT-T(s)F stimulated the development of cells which, aider transfer, are able to suppress the GAT PFC response to GAT-MBSA. The cells responsible for this suppression were shown to be T lymphocytes by using nylon wool-purified T cells for suppressor cell induction and by eliminating suppressive activity in cells cultured with crude GAT-T(s)F by treatment with anti-Thy 1.2 plus C before transfer. The suppressor T cells act in a specific manner failing to suppress significantly either anti-sheep erythrocyte or trinitrophenyl-ovalbumin primary PFC responses. For the induction of GAT-specific suppressor T cells in culture, a moiety bearing H- 2(K(q) or I(q)) determinants and also GAT, either bound to the crude GAT- T(s)F or added in nanogram amounts to antigen (GAT)-free purified GAT-T(s)F, were both required.

After appropriate in vivo or in vitro immunization, cytotoxic T lymphocytes (CTL) are generated which efficiently kill cells bearing particular membrane antigens in common with the immunizing cell (reviewed in reference 1). Such CTL have been most thoroughly studied in mice, employing alloimmunization with cells differing at the major histocompatibility locus, H-2. in such cases, the predominant cell surface antigens recognized by the CTL appear to be the molecules carrying the serologically defined H-2 specificities, coded for by the K and D regions of the H-2 complex (2). In other syngeneic models of cell-mediated specific cytolysis, involving lymphocyte chariomeningitis (LCM) virus- or ectromelia virus-infected cells or TNP-modified lymphoid cells, thymus-derived cells also constitute the main effector cell type. The CTL generated in these latter systems function most efficiently when virus-infected or TNP-modified target cells share identitites at the H-2K or H-2D loci with the effector CTL and stimulator cells (3-5). Another set of experimental systems in which CTL are generated and play a significant biological role is that of immunity to tumor-associated antigens (TAA) (6). The nature of the TAA which the CTL recognize is only beginning to be understood. Several recent reports indicated the existence of physiochemical and/or antigenic relationships between TAA and H-2 antigens (7,8). These relationships, together with the genetic restrictions cited above in the generation of CTL involving products of the H-2K or H-2D loci suggested the possibility that in certain tumor systems, the TAA which are able to most effectively stimulate CTL responses might be structurally similar to, or linked with, the H-2K or H- 2D molecules on the tumor surface. It has been previously demonstrated in allogenic models that antisera specific for the appropriate H-2K or H-2D products present on a target cell could specifically block CTL-mediated lysis (1,9). This report demonstrates that certain anti-H-2 alloantisera specific for the target tumor cells can block lysis of those target cells mediated by syngeneic tumor-specific CTL effector cells.