Monoclonal suppressor factor specific for lactate dehydrogenase B. I. Mechanism of interaction between the factor and its target cells

The in vivo antibody response to hen egg white lysozyme in H-2b-compatible responder and non-responder mice: is it regulated by its N-terminal peptide at the level of antigen-presenting cells?

We studied the in vivo antibody responses of three H-2b strains, BALB/b, C57BL/6 and BALB/B x C57BL/6 F1 to various lysozymes, REL and HEL, after priming with HEL, REL or the HEL N-terminal peptide. It was confirmed that C57BL/6 is a non-responder strain to HEL and that BALB/b is responder strain. The C57BL/6 non-responder trait was associated with HEL or peptide induction of suppressor cells, as shown by adoptive transfer experiments. We further demonstrated that the suppressor/non-responder trait is dominant in BALB/b x C57BL/6 F1 hybrids and that appropriately pulsed macrophages of BALB/b mice can bypass such suppression in these F1 mice. Possible mechanisms are discussed.

Downregulation of helper T cells by an antigen-specific monoclonal Ts factor

The findings of previous studies in this laboratory demonstrating that conjugates of human monoclonal (myeloma) IgG (HIgG) and monomethoxypolyethylene glycol (mPEG) were able to induce in mice antigen-specific tolerance and CD8+ suppressor T (Ts) cells were confirmed in the present study. An extract (TsF) of a nonhybridized clone of Ts cells (viz., clone 23.32), which had been derived from spleen cells of mice tolerized with HIgG(mPEG)26, was shown to possess antigen-specific suppressive activity. This monoclonal TsF was able to specifically suppress in vitro antibody formation only if it was present from the beginning of the culture. From the results of the cellular dissection of the system used it was concluded that (i) the TsF had no effect on fully differentiated primed B cells or plasma cells, and (ii) the TsF inactivated carrier-primed Th cells when the culture contained concomitantly naive CD8+ T cells, accessory cells, and antigen. These data support the view that the monoclonal TsF exerted its downregulating effect on Th cells only if it could first interact with a CD8+ T cell, in the presence of accessory cells and antigen.

Mechanism of MHC class II restriction in the interaction between specific suppressor and responder T cells in a proliferative response: Ia interaction with a putative anti-self receptor, expressed on pre-activated responder cells

For the inhibition of T-lymphocyte proliferation in mixed lymphocyte culture (MLC) by in vivo alloantigen-induced specific T-suppressor cells (Ts), the Ts and responder cells must have major histocompatibility complex (MHC) class II identity, either in I-C or in I-A + I-E. In the case of I-C, the molecule is on the surface of the Ts and not on the surface of the stimulator or responder cells. This lack of I-C on the responder cells occurs even after pre-activation by antigen. I-J on the Ts is unimportant in the present system. By blocking the Ts surface molecules with antibody, it was shown that the two Ts genetic restrictions were due to distinct Ts subsets, bearing I-C in one case and I-A + I-E in the other. Pretreatment of the Ts with anti-I-C antibodies (without complement) did not prevent specific Ts binding to the alloantigen, as shown by absorption on monolayers. However, it blocked the ability of the Ts to cause suppression and this could be reversed by removal of the antibody with pronase. The responder population, when pre-activated, could be fractionated by absorbing on monolayers of syngeneic Ts. Under these conditions, the cells sensitive to suppression adhered to the monolayer, while the non-adherent cell could not be suppressed. It is proposed that a receptor, to an Ia molecule (I-C or I-A + I-E) of the Ts, appears on the surface of the pre-activated responder T cell and that this is required for the genetically restricted interaction between the responder cell and the Ts.

Suppressor T-cell abnormality in NOD mice before onset of diabetes

To investigate the pathological role of suppressor T-cells in non-obese diabetic (NOD) mice, we stimulated splenic T-lymphocytes from diabetes-prone NOD mice with concanavalin A (ConA) and then evaluated their ability to suppress the lymphocyte-proliferative responses to mitogen and allogenic cells. Lymphocytes from NOD mice showed significantly less suppressor ability than did those from BALB/c mice and non-obese non-diabetic (NON) mice, the corresponding non-diabetic sister strain of the NOD mouse, both in the mitogen response and in the mixed lymphocyte reaction (MLR). We used monoclonal antibodies and flow cytometry to analyze the lymphocytic surface phenotypes, and found markedly fewer Lyt2+ T-lymphocytes (suppressor/cytotoxic T-lymphocyte) in the NOD mice than in both controls after exposure to ConA. These results suggest that suppressor T-cell activity is already depressed in NOD mice before diabetes begins and that a substantial decrease in the number of suppressor T-cells induced by ConA may explain this depressed suppressor activity. This impairment may contribute to the pathogenesis of type 1 diabetes in NOD mice.

An adjunct trait of HEL/I-Ab-specific T helper cell is sensitivity to antigen-specific immunosuppression

The present study tests whether the specific inhibition of helper T (Th) cell (and T hybridomas) by suppressor T (Ts) cells is a phenotypic trait of Th cells correlating with their acquired specificity for antigen/major histocompatibility complex or a genotypic trait not related to selection of the T cell repertoire for antigen. To do this we took advantage of the fact that H-2d parental strains of mice commonly restrict recognition of chicken egg-white lysozyme to the L3 peptide (a.a. 105-129) and H-2b parental mice to the L2 peptide (a.a. 13-105). F1 hybrids of these strains display two subsets of lysozyme-reactive T cells, one for each parental phenotype. Using (B10 X B10.D2)F1 mice reconstituted with B10.D2 bone marrow, we were able to develop genetic H-2d T cell clones that could express an atypical specificity, that is L2/I-Ab. Clones of this type, like genetic H-2b, are also sensitive to the inhibiting effects of HEL-activated Ts cells. To overcome some of the drawbacks of using heterogeneous populations of T, B and accessory cells in our assays, we constructed T hybridomas from HEL-immune, chimeric lymph node T cell blasts which respond to a unique antigen/major histocompatibility complex with production of the lymphokine interleukin 2. Our results indicate that all HEL/I-Ab-specific T cells (helper and hybridomas) are inhibited by suppression regardless of the T cell's haplotype at the H-2 locus: H-2b (B10), H-2d (D2) or H-2b,d (BDF1). Furthermore, there is a strict correlation between the antigen and I-A specificity: I-Ab-restricted T cells recognize non-L3 determinants even though some are derived from H-2d mice.

Immunoregulation of lysozyme-specific suppression. III. Epitope-specific amplification of immunosuppression induced by monoclonal suppressor-T-cell products

The hen egg-white lysozyme (HEL)-specific suppression induced by soluble molecules produced by a monoclonal T-cell lymphoma line (LH8-105) obtained from HEL-specific suppressor T lymphocytes has been examined. Injection of I-J+ molecules from LH8-105 cell culture supernatant (TsFa) in HEL-primed mice during the afferent phase of the response induced Lyt-2+ second order suppressor T (Ts) cells which, upon transfer into HEL-CFA-primed syngeneic recipients, inhibit the delayed-type hypersensitivity (DTH) response to HEL. Transfer of spleen cells from TsFa-injected mice primed with HEL or human lysozyme suppresses the DTH response to HEL in recipient mice whereas this response is not affected by cell transfer from ring-necked pheasant egg-white lysozyme (REL)-primed and TsFa-injected mice, indicating that induction of second order Ts by TsFa is specific for a lysozyme epitope including phenylalanine at position 3. Fine antigenic specificity of second order Ts-cell induction is confirmed by similar results obtained upon injection of TsFa in mice primed with HEL N-terminal synthetic peptide or with an analog in which, as in REL, phenylalanine has been substituted by tyrosine at position 3. The same fine antigenic specificity observed in the induction of second order Ts cells is also present in the expression of TsFe suppressive activity. The similar antigenic specificity of Tsa and Tse suggests that Tse cells could result from amplification of the Tsa cell population or these two cell subsets could reflect different maturation stages of the same cell type rather than distinct T-cell populations activated in cascade.

Antigen-specific, I-A-restricted suppressor hybridomas with spontaneous cytolytic activity. Functional properties and lack of rearrangement of the T cell receptor beta chain genes

T suppressor (Ts) hybridomas were produced by fusion of the III/4 T cell hybridoma with splenic T cells from CBA mice tolerized with subimmunogenic doses of bovine serum albumin (BSA). Both the Ts hybridoma cells and a suppressor factor (TsF) inhibited in an antigen-specific and I-Ak-restricted fashion the in vitro proliferative response of BSA-immunized lymph node cells. In addition to the suppressive activity, the hybridoma lines displayed spontaneous cytotoxicity against various tumor targets. The isolation of Ts subclones that are suppressive but not cytolytic, as well as the existence of the noncytolytic TsF, indicates that suppression of antigen-specific T cell proliferation is not dependent on cytolytic activity. The Ts hybridomas were I-A restricted, as are many T helper cells. Therefore, a potential similarity with respect to antigen receptor genes was expected. Southern blot analysis with a probe specific for genes encoding the beta chain of the T cell receptor on T helper and T killer cells revealed no rearrangement of the beta genes in the Ts cells. The data imply that neither the antigen receptor on the I-A-restricted Ts cells nor the receptor involved in the cytolytic interaction with tumor targets use the same beta chain constant region as T helper and T killer cells.

I-J as a restriction element in the suppressor T cell system

This review attempts to sort out the differences between macrophage and T cell I-J determinants. We propose that suppressor T cells have receptors for self-I-J determinants which are expressed on macrophage-like accessory cells. The I-J determinants associated with accessory cells are responsible for the selection of the Ts receptors. Although the major histocompatibility complex is involved in the selection of Ts receptors, the receptors themselves need not be encoded by genes which reside within the MHC. In fact, the molecular genetic evidence presently available has established that suppressor T cell factors do not express gene products associated with the postulated I-J region of the H-2 complex. In spite of the failures of biochemists and molecular geneticists to identify I-J genes and gene products, there is extensive biological data demonstrating the existence of I-J. The activity of anti-I-J reagents has been verified by numerous laboratories. Sera containing anti-I-J activity have been prepared in many strain combinations. Immunization between a variety of strains differing at the purported I-J region produce active anti-I-J antibodies (Murphy et al. 1976, Tada et al. 1976, Pierres et al. 1977, Tada et al. 1978). Furthermore, in many suppressor cell systems the interactions of Ts cells and factors are restricted by I-J (Tada & Okumara 1980, Sorensen & Pierce 1982, Green et al. 1983, Dorf & Benacerraf 1984). Most investigators who have attempted to detect I-J have analyzed T cells. Since we propose that T cells express a complementary anti-I-J receptor, subsequent efforts at identifying I-J should include analysis of macrophage I-J determinants. In spite of extensive biological data, we still do not know if I-J is a protein, carbohydrate or lipid. In addition, the role of H-2 in determining I-J structure is unknown. Nevertheless, the overwhelming biological data demonstrate that I-J is an important structure for suppressor T cell interactions. Much remains to be accomplished, including the characterization of I-J products and locating the I-J genes.

Composition of a suppressor factor that inhibits the immune response to lactate dehydrogenase B

Hybridomas obtained by fusion of lactate dehydrogenase B (LDHB)-activated suppressor T (Ts) cells with the BW5147 thymoma produce a suppressor factor (TsF) that inhibits the proliferation of LDHB-activated helper T (Th) cells. A similar factor (TsE) is contained in the extract of suppressor hybridomas. Both TsF and TsE are specifically retained by LDHB-immunoadsorbent columns. Both consist of two components, an antigen-binding component (ABC) and possibly a major histocompatibility complex (MHC) component. The latter reacts with certain monoclonal antibodies specific for MHC determinants. The two components are covalently associated in the TsF and noncovalently associated in TsE. Mixing of the two components reconstitutes the activity of the TsF or TsE. Disruption of the ABC's tertiary structure results in its inability to reconstitute suppressive activity on mixing with the MHC components. The ABC may contain an intrachain disulphide bond(s). Suppression is obtained when Th cells are incubated first with the ABC and then with the MHC component or vice versa, provided that the incubation period is at least 4 h. The MHC component is also produced by nonsuppressor hybridomas but not by mitogen-stimulated blasts or by the parental thymoma. The TsF is a glycoprotein with a molecular weight of about 120,000 to 160,000. The molecular weight of the ABC is about 76,000-86,000 and of the MHC component about 30,000-37,000.

Feedback regulation of immune suppression by a suppressor factor

Mouse hybridomas generated by fusion between a lactate dehydrogenase-B (LDH-B)-specific B10.A(2R) T suppressor (Ts) cell line and the BW5147 thymoma secrete two suppressor factors, TsF-A and TsF-E. The factors carry the same antigen-binding chains but different major histocompatibility complex (MHC) chains (A beta-like and E beta-like, respectively). The TsF-A suppresses the proliferation of A-restricted, LDH-B-specific T helper (Th) cells. In this report we demonstrate that the addition of the TsF-E (isolated on immunosorbent columns with Ek- or Jk-specific antibodies) to the culture of LDH-B-primed B10.A(2R) lymph node cells turns the nonresponder (suppressed) cultures into proliferating ones, and that this change is antigen specific. This enhancing effect occurs in the early phase of the cell culture; the factor has no effect when added 2 days after the initiation of the culture. Because pretreatment of the Ly-2+ but not of the Ly-1+2- cells with TsF-E induces responsiveness, it is very likely that the targets of the factor are the Ts cells or their precursors that belong to the Ly-2+ subset. An incubation period of about 4 h is necessary for the TsF-E to exert its action. The enhancing effect of the TsF-E is abrogated by monoclonal antibodies specific for Ek and Jk antigenic determinants. However, only some of the antibodies that retain the TsF-E on the immunosorbent column neutralize the factor in a functional test. Antibody blocking studies also indicate that the MHC determinants involved in the interaction between the antigen-presenting and the Ts cell during Ts cell activation, and in the TsF-E Ts cell interaction are either very similar or identical. We interpret the data as indicating that the Ts cells or their precursors recognize the TsF-E with the same receptors as they use for the recognition of LDH-B together with the Ek on the antigen-presenting cells. The recognition of the TsF-E inactivates the Ts cell so that proliferation of Th cells then occurs unhindered. Thus, the production of the TsF-E may provide a feedback mechanism that regulates the activation of the Ts cells and, consequently, the degree of suppression in the response to LDH-B.

Suppressor T cell growth and differentiation. Identification of a cofactor required for suppressor T cell function and distinct from interleukin 2

This report describes a Ts costimulator assay and its use to analyze cofactors required for the expression of suppressor T cell function. Activation of primed MLR-Ts (alloantigen-activated suppressor T cells suppressive of mixed leukocyte reaction) to suppressor T cell factor (TsF) production typically fails in the presence of glutaraldehyde-fixed rather than irradiated allogeneic stimulator cells. However, MLR-TsF production was restored by the addition of 48-h primary MLR supernates; MLR-derived Ts costimulator neither activated primed MLR-Ts in the absence of fixed allogeneic stimulators nor directly suppressed assay MLR. Lack of antigen specificity or genetic restriction and failure to activate unprimed MLR-Ts precursors suggested that Ts costimulator activity differed from previously described Ts inducer functions and was more closely aligned with the lymphocyte- or monocyte-derived interleukins (IL). Three findings distinguished Ts costimulator from IL-2. Depletion of IL-2 activity from MLR supernates by HT2 adsorption failed to affect Ts costimulator function. In addition, MLR supernates prepared in the presence of cyclosporin A contained no IL-2 but expressed Ts costimulator activity. Finally, gel chromatography demonstrated Ts costimulator in peaks of 21,000 and 43,000 mol wt that were largely distinct from the IL-2-containing fractions. Ts costimulator activity was also identified in phorbol myristate acetate (PMA)-induced EL4 supernates and was retained in those supernates after IL-2 depletion by HT2 adsorption. In preliminary functional characterization, MLR supernate-derived Ts costimulator triggered MLR-TsF production from irradiated MLR-Ts in the absence of proliferation. Thus a differentiative rather than proliferative stimulus required for primed MLR-Ts function appears to be provided by this Ts costimulator and has been provisionally termed Ts differentiative factor ( TsDF ). This initial characterization may thus identify one of a possibly distinctive family of interleukins required in the alloantigen-driven activation of suppressor T cells to effector function.

Evidence for two suppressor factors secreted by a single cell suggests a solution to the J-locus paradox

The hybridoma produced by the fusion of lactate dehydrogenase-B (LDH-B)-primed B10.A(2R) mouse suppressor T (Ts) cells with the BW5147 thymoma secretes two kinds of T suppressor factors (TsF), TsF-A and TsF-E. The TsF-A suppresses A beta-restricted and the TsF-E, E beta-restricted helper T (Th) cells. Each of the two factors consists of two polypeptide chains, an antigen-binding chain (ABC) and a major histocompatibility complex (MHC) chain. The ABC binds LDH-B, which is then recognized by one of the two receptors of the Th cell and an antigen bridge is formed between the factor and the Th cell. This chain is presumably identical in both factors. The MHC chain of the TsF-A carries antigenic determinants recognized by three sets of monoclonal antibodies: antibodies specific for the A beta chain, antibodies specific for class II determinants expressed in T cells and controlled by the A beta-E beta chromosomal segment, and antibodies crossreacting with J determinants. The MHC chain of the TsF-E carries determinants recognized by E beta-specific and by J-specific antibodies. Only some of these serologically detectable determinants reside in the region of the TsF molecule recognized by Th cells. These findings suggest that the J determinants are carried by the modified E beta and also by the modified A beta chains.