Soluble factors in tolerance and contact sensitivity to 2,4-dinitro-fluorobenzene in mice. IX. A monoclonal T cell suppressor molecule is structurally and serologically related to the alpha/beta T cell receptor

Ts cells from mice tolerized with dinitrobenzene sulfonate produce a DNP-specific, MHC-restricted soluble suppressor factor (SSF) which regulates contact sensitivity to 2,4-dinitro-fluorobenzene. Previous studies have shown that the SSF-producing T cells and the soluble factor have the same hapten/MHC specificity suggesting that SSF may represent a secreted form of the Ts membrane receptor. The relationship between TCR proteins and SSF was investigated by examining the structural and serologic properties of a monoclonal DNP/H-2Kd-specific suppressor molecule produced by a Ts hybridoma. Reduction followed by alkylation abrogated the ability of the 3-10 molecule to inhibit transfer of contact sensitivity to 2,4-dinitro-fluorobenzene, indicating that intact disulfide bonds were a required structural property for suppression. Reduction of the 3-10 molecule followed by affinity chromatography on DNP-coupled Sepharose beads indicated that the 3-10 suppressor molecule is a dimer and that one of its chains binds to cell-free DNP. Serologic properties of the 3-10 molecule were examined by determining the ability of pan-reactive rabbit anti-TCR antibodies and anti-V beta 8 mAb KJ16.133 and F23.1 to adsorb suppressor activity from 3-10 culture supernatant and affinity purified 3-10 ascites material. All three reagents adsorbed the suppressor activity whereas control antibodies had no effect. When 3-10 material was passed through a F23.1-conjugated Sepharose affinity column, suppressor activity was recovered in the column eluate but not in the effluent fraction. When the 3-10 molecule was reduced and separated into its two chains (i.e., DNP-binding and non-DNP-binding chains), it was found that the anti-V beta 8 antibody F23.1-bound to the non-DNP-binding chain of the suppressor molecule. Collectively, these results indicate that the monoclonal 3-10 suppressor molecule is structurally similar to the alpha/beta TCR and suggest that the 3-10 molecule expresses a determinant encoded by the V beta 8 family of TCR genes. These results are consistent with our hypothesis that these suppressor molecules represent a secreted form of the TCR expressed on the surface of the DNP-specific Ts.     

Selective induction of delayed hypersensitivity T-effector and T-suppressor lymphocytes in vitro by haptenized bone marrow-derived macrophages

The role of various subpopulations of antigen-presenting macrophages in the induction of T-lymphocyte subpopulations has been difficult to study in the past. We have used an in vitro system of bone marrow cell culture both to induce T-effector (TDH) and T-suppressor (Ts) cells active in delayed-type hypersensitivity. Bone marrow-derived macrophages (BM-MA) grown in Teflon bag cultures were allowed to attach to culture dishes and were pulse-labeled with 2,4-dinitrobenzene sulfonate (DNBSO3). Spleen cell lymphocytes from nonsensitized BALB/c mice were cocultured with antigen-pulsed or control BM-MA for 3 days. The lymphocytes were harvested, and injected iv into BALB/c mice which were challenged within 1 hr after injection by painting the right ear with 2,4-dinitrofluorobenzene (DNFB, effector test) or sensitized with DNFB on 2 days following iv injection of the cells and challenged 5 days later (suppressor test). Ear swelling was measured 24 hr later to assess the effector or suppressor function of the in vitro educated lymphocytes. BM-MA grown for 5 days (BM-MA 5) in L-cell conditioned medium induced only TDH cells (Thy 1+, Lyt 1+2-) whereas BM-MA grown for 10 days in conditioned medium induced only Ts cells (Thy 1+, Lyt 1-2+). In both cases, induced TDH and Ts cells were antigen specific. Functionally, induced Ts cells suppressed the afferent limb of the delayed response. When DNP-BM-MA 5 and DNP-BM-MA 10 were used to induce TDH or Ts cells in vivo by subcutaneous or intravenous injection respectively, only BM-MA 5 were able to sensitize recipient mice. Both 5- and 10-day macrophage populations induced Ts cells in vivo. Functionally, these Ts cells appeared to act on the efferent limb of the delayed reaction. We conclude that different populations of antigen-presenting macrophages can preferentially induce TDH or Ts cells, perhaps depending on antigen presentation in association with class II antigens or on the functional state of the antigen-presenting cell.     

Antibody-mediated regulation of T cell responses. I. Characterization of a monoclonal antibody which specifically regulates contact hypersensitivity to DNFB in BALB/c mice

Contact hypersensitivity (CS) to 2,4-dinitrofluorobenzene (DNFB) in BALB/c mice is regulated by autoanti-idiotypic antibody. This report describes the preparation and characterization of a monoclonal antibody, 2-16.1, which has characteristics previously described for the serum anti-idiotypic antibodies. Monoclonal 2-16.1 was prepared by fusing lymph node (LN) cells from optimally sensitized BALB/c mice to the P3X myeloma. The monoclonal product of the cloned hybridoma is an IgM (K) immunoglobulin which does not bind to DNP-protein but which does bind to other immunoglobulins with anti-DNP specificity, primarily of the IgM class. Functionally, 2-16.1 inhibits the efferent limb of the CS reaction as measured by passive transfer of immunity. This inhibition is antigen-specific and appears to require the presence of a subset of Ia+ T cells in the DNFB-immune LN cell population. Suppression of transfer of immunity is strain-specific. Finally, suppression occurs only in the absence of complement, indicating that a lytic mechanism is not involved and that 2-16.1 does not recognize determinants expressed on the effector T cells of the CS reaction. Collectively, these results indicate that 2-16.1 is a monoclonal anti-idiotypic antibody, and that the hybridoma CSDNP 2-16.1 represents a clone of B cells which is stimulated during the primary CS response to DNFB and whose antibody product is involved in the endogenous, active regulation of this T cell-mediated response.     

Suppressor T cell circuits in contact sensitivity. II. Induction and characterization of an efferent-acting, antigen-specific, H-2-restricted, monoclonal T cell hybrid-derived suppressor factor specific for DNFB contact hypersensitivity

This report defines a methodology for the production and characterization of an antigen-specific, monoclonal T cell hybrid-derived suppressor T cell factor (TsF) that suppresses the passive transfer of 2,4-dinitrofluorobenzene (DNFB) contact hypersensitivity. Fusion of T cells from BALB/c (H-2d) mice tolerized with syngeneic DNP-spleen cells to BW 5147 thymoma cells resulted in several hybrids that constitutively produce a soluble regulatory molecule. One of these hybrids, 26.10.2, was subsequently cloned, and its soluble factor was characterized with respect to its antigen specificity, biochemical nature, MHC restriction pattern, and identity of its target cell. 26.10.2 TsF suppresses the passive transfer of delayed-type hypersensitivity (DTH) mediated by DNP- but not trinitrochlorobenzene- or oxazalone-primed DTH T cells (TDH) after a 1 hr incubation at 37 degrees C. In contrast, 26.10.2 TsF had no suppressive effect on secondary in vitro DNP-specific T cell proliferative responses. 26.10.2 TsF therefore represents an antigen-specific factor with effector (efferent-acting) function. The monoclonal TsF was shown to consist of a two-chain, disulfide-bonded molecule, and to bear a receptor(s) specific for DNP and determinants encoded by the I region of the H-2 complex. Effector suppressive activity of 26.10.2 TsF was restricted by Class I H-2Dd determinants. One cellular target of this monoclonal factor was shown to be the DNP-specific TDH cell, because DNFB-primed lymph node cells from cyclophosphamide-pretreated donors (lacking Ts-auxiliary (Ts-aux) cells) were efficiently suppressed. The TsF appears to focus on passively bound, TDH receptor-associated, DNP-Class I determinants, as suggested by the observation that freshly prepared, but not overnight cultured, DNP-specific TDH cells were susceptible to suppression.     

Effect of methanol extraction residue tubercle bacillus fraction treatment in vivo and in vitro on the release and activity of suppressor factor inhibiting the efferent phase of contact sensitivity in mice

BALB/c mice subjected to injection of dinitrobenzenesulfonate (DNBSO3) and skin painting with dinitrofluorobenzene (DNFB) produce splenic T-suppressor (Ts) cells that, when transferred to DNFB-sensitized recipients, suppress the efferent (eff) phase of contact sensitivity (CS). Splenocyte populations containing such Ts-eff cells release a specific soluble suppressor factor (SSF) in vitro that similarly suppresses CS in sensitized recipient mice. Treatment with the methanol extraction residue (MER) tubercle bacillus fraction, a known immunomodulating agent, of animals exposed to DNBSO3 and DNFB ("DNBSO3-DNFB" donors) prevented release of SSF by their spleen cells at in vitro incubation. Incubation of DNBSO3-DNFB donor splenocytes with MER in vitro also abolished SSF release, and treatment with MER of test animals prior to DNFB sensitization prevented the suppressive action of subsequently administered SSF. The observations are discussed with regard to the potentiating capacities of MER on cellular immunity and states of resistance.     

Suppressor T cell mechanisms in contact sensitivity. II. Afferent blockade by alloinduced suppressor T cells.

We investigated the mechanism(s) by which MHC-restricted suppressor T cells (Ts) induced by i.v. injection of allogeneic DNP-modified lymphoid cells (alloinduced Ts) suppress the DNFB contact sensitivity response. It was shown that alloinduced Ts acted only during the early phases (afferent limb) of sensitization. They were incapable of suppressing previously sensitized recipients or of inhibiting the expression of DNFB-immune LN cells when co-transferred into normal recipients. The target of alloinduced Ts seems to be cell proliferation, i.e., inhibition of antigen-induced cell proliferation (DNA synthesis) in Ts recipient mice. The failure of recipients of alloinduced Ts to generate DNFB-immune LN cells capable of transferring contact sensitivity to normal recipients also suggests that these Ts act by preventing the development of an expanded clone of mature immune T cells. The suppressive effects of alloinduced Ts also were inhibited by prior in vitro treatment with anti-TNP serum. The data are discussed in terms of current models of suppression, and are compared to mechanisms of suppression in other contact sensitivity models.     

Tolerance and contact sensitivity to DNFB in mice. VII. Functional demonstration of cell-associated tolerogen in lymph node cell populations containing specific suppressor cells.

Adoptive tolerance to contact sensitivity to DNFB is mediated by suppressor T cells. These cells are induced by iv injection of the hapten DNB-SO₃. Experiments were carried out to investigate the question of simultaneous transfer of tolerogen (DNB-SO₃ or its conjugation product DNP) with the suppressor cells. The results showed that tolerant lymph node cells pretreated in vitro with anti-TNP serum before transfer were unable to induce unresponsiveness to DNFB. Tolerant cells treated with either anti-TNP serum which had been passed over a TNP-affinity column or with polyvalent anti-immunoglobul in serum were not inhibited. These results functionally demonstrate that LN cell populations containing DNFB suppressor cells have accessible hapten (e.g., DNP) associated with their membrane, which is necessary for induction of adoptive tolerance. The hapten (tolerogen) appears to be bound directly to the cell surface rather than as an immune complex.     

Suppressor T cell circuits in contact sensitivity. III. A monoclonal T cell hybrid-derived suppressor factor specifically suppresses local DTH transfer by a DNP-specific T cell clone

Herein we described the direct suppressive effects of a monoclonal T cell hybridoma-derived, DNP-specific suppressor T cell factor (26.10.2 TsF) on the local transfer of delayed-type hypersensitivity (DTH) by a DNP-specific BALB/c T cell clone (dD1.9). The L3T4+, Lyt-2- dD1.9 T cell clone proliferated in response to DNP-OVA and DNBS, but not TNP-OVA or TNBS, in association with I-Ed determinants present on antigen-presenting cells. Similarly, local injection of histopaque-purified dD1.9 cell blasts resulted in DNP-specific, radioresistant, I-Ed-restricted, mononuclear cell-rich ear swelling responses. Incubation in 26.10.2 TsF specifically suppressed local transfer of DNP-specific DTH by dD1.9, but not local DTH responses transferred by BALB/c T cell clones specific for TNP or GAT. The suppressive effect of 26.10.2 TsF correlated with targeting on DNP-major histocompatibility complex determinants associated with the DTH T cell (TDH) targets. 26.10.2 TsF-mediated suppression was most pronounced after exposure of dD1.9 target cells to antigen (after the stimulation phase of the T cell clone maintenance procedure), and greatly reduced when dD1.9 was cultured for long periods in the absence of DNP (after the rest phase of clone maintenance). In additional support of this hypothesis, GAT-specific TDH, normally resistant to 26.10.2 TsF-mediated suppression, were rendered susceptible to suppression after surface DNPylation. The results demonstrate a direct, antigen-specific, effector phase regulatory effect of a monoclonal TsF on a cloned, antigen-specific T cell target, and strongly suggest that suppression is mediated via targeting on DNP determinants associated with the TDH target. Simplification of complex Ts circuitry operating in suppression of the efferent limb of DTH by the use of monoclonal TsF and cloned T cell targets should provide a basis for the future study of the molecular mechanisms of immune suppression.     

Prethymic T cell precursors express receptors for antigen

An anti-idiotype serum raised in BALB/c mice against syngeneic lymph node T cells from 2,4-dinitrofluorobenzene (DNFB)-sensitized mice was used to study the early expression of antigen receptors on developing T cells. Normal BALB/c bone marrow cells were treated with either anti-Thy-1.2 plus complement or anti-Thy-1.2 and anti-idiotype plus complement before use in the reconstitution of lethally irradiated syngeneic mice. Five weeks after reconstitution, recipient mice were assayed for both contact sensitivity (CS) and in vitro proliferative responses to DNFB. Mice reconstituted with bone marrow cells treated with both anti-Thy and anti-idiotype sera showed a significant decrease in reactivity to DNFB in both assay systems when compared with mice reconstituted with marrow treated with anti-Thy only. CS response to the noncross-reacting hapten oxazolone was identical in both recipient groups. Bone marrow mixing experiments showed no evidence of anti-idiotype-induced suppressor cells in these experiments. These data provide strong evidence that at least some T cell precursors express receptors for antigen prethymically.     

Inhibition of the T suppressor circuit of delayed-type hypersensitivity by interferon

The effects of electrophoretically pure murine interferon (Mu-IFN-alpha beta) on the T suppressor pathway and on the T effector cell of delayed hypersensitivity (TDH) were investigated in BALB/c mice, in a 2,4-dinitrofluorobenzene (DNFB) contact-sensitivity model. Various T cell subpopulations, suppressor T cells of the afferent (Ts-aff) and efferent (Ts-eff) types, an auxiliary Ts (Ts-aux), as well as TDH were induced, and their function was assessed in transfer experiments. The results were as follows. At a dose of 5 X 10(3) U, IFN was shown to inhibit the Ts-aff response, when given to the donor animal shortly after induction of the Ts-aff subpopulation or when injected into the recipient 2 hr after spleen cell transfer. Pretreatment in vitro with IFN of the splenic cells to be transferred also abolished the Ts-aff response. Similar amounts of IFN were able to inhibit the generation of Ts-eff in the donor animals, whereas 10-fold-higher amounts were needed in vivo or in vitro to block the functional expression of Ts-eff in the recipient animal. Intravenous injection of IFN into recipients of Ts-eff on day 0 and 1 after sensitization inhibited the expression of the Ts-eff transferred 1 day before ear challenge. This suggests that the Ts-aux response required for the TDH suppression by Ts-eff is blocked by IFN. Secretion of a suppressor factor by Ts in vitro was not blocked by IFN. Treatment of the donor of suppressor factor-secreting Ts with IFN, however, blocked the induction of this Ts. The TDH were not sensitive to IFN even at amounts approximately 100 times higher than those used for the Ts inhibition in vivo as well as in vitro. These results demonstrate that low amounts of IFN may selectively block the suppressor pathway, because induction of these regulatory T cell subsets appears to be particularly sensitive to IFN. The exact mechanism of the IFN-mediated inhibition of Ts is not yet clear. The data suggest an important regulatory function of IFN in delayed-type hypersensitivity (DTH) reactions.     

Sensitization through carcinogen-induced Langerhans cell-deficient skin activates specific long-lived suppressor cells for both cellular and humoral immunity

Application of 2,4-dinitrofluorobenzene (DNFB) to BALB/c mouse skin depleted of epidermal Langerhans cells (LC) by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) activated cells which suppress both contact sensitivity and antibody production when transferred into naive host mice. Tolerance was induced by a concentration of DNFB optimal for inducing contact sensitivity in solvent-treated control mice. The cellular and humoral responses of hosts to a second antigen, 2,4,6-trinitrochlorobenzene (TNCB), were unaffected by these suppressor cells, demonstrating specificity for DNFB. Suppressor cells for cellular and humoral immunity could still be demonstrated 6 months following activation, by which time some mice had died, presumably of old age. The dose responses to sensitizer for generation of cells which suppressed contact sensitivity and antibody production differed, indicating that separate populations of suppressor cells probably inhibit these responses. Hence, during cutaneous chemical carcinogenesis, depletion of LC may allow activation of specific long-lived suppressor cells capable of inhibiting cellular or humoral antitumor immune responses.     

Induction of CD8+ suppressor T cells by treatment with DMBA and TPA in vitro.

Antigen-nonspecific CD8+ T suppressor cells, which suppressed delayed-type hypersensitivity (DTH) against sheep red blood cells in BALB/c mice, were induced by incubating spleen cells from mice treated with 7,12-dimethylbenz[a]anthracene (DMBA), a tumor initiator, with 12-O-tetradecanoylphorbol 13-acetate (TPA), a tumor promoter. The optimal condition was incubation in 3.2 x 10(-8) mol/5 ml of TPA for 4 days. It was shown that induction of the suppressor cells required macrophages from mice treated with DMBA. These data were consistent with the results of previous work, in which CD8+ suppressor cells were induced by painting BALB/c mice with TPA following DMBA treatment. DTH was suppressed in the culture supernatants of spleen cells from mice treated with DMBA and TPA; the suppression was genetically unrestricted. The suppressor factor was resistant to trypsin and sensitive to heating at 56 degrees C for 30 min and had affinity for the macrophages.     

Suppressor cells for the afferent phase of contact sensitivity to picryl chloride: inhibition of DNA synthesis induced by T cells from mice injected with picryl sulfonic acid.

Previous reports have shown that picryl sulfonic acid (PSA) induces suppressor T cells that inhibit the effector phase of contact sensitivity, whereeas its DNP counterpart, dinitrobenzenesulfonate (DNBS) induces cells that inhibit the afferent phase of sensitization. Accordingly, cells from mice injected with DNBS, but not PSA, could be shown to inhibit the DNA synthesis in the lymph nodes that occurs during sensitization. It is now shown that PSA does induce T cells that suppress DNA synthesis but this can only be detected with enriched T cells or by using a regimen of PSA injection different frm previously used to induce suppressor cells for the effector phase. The T cells did not affect responses to oxazolone or dinitrofluorobenzene (DNFB) and were distinguishable from suppressors of the efferent phase in that they could be produced in adult thymectomized but not cyclophosphamide-treated mice. T cells from mice injected with DNBS that inhibited DNA synthesis to DNFB had the same properties.     

Tolerance and contact sensitivity to DNFB in mice. VI. Inhibition of afferent sensitivity by suppressor T cells in adoptive tolerance.

Tolerance in contact sensitivity to DNFB can be adoptively transferred to normal mice with lymph node cells from tolerant donors. This tolerance is antigen specific and is mediated by T cells, i.e., "suppressor" T cells. Experiments were carried out to investigate the mechanism(s) by which the suppressor T cells induce tolerance to DNFB contact sensitivity. The suppressor cells were effective only if they were present during the early stages of the afferent limb of sensitization. As measured by DNA synthesis, cell proliferation in the draining lymph nodes of recipients of suppressor cells was found to be significantly less than in control animals indicating that the suppressor cells acted, at least in part, by limiting or inhibiting DNFB-induced cell proliferation. This inhibition was shown to be antigen specific since the DNFB suppressor cells did not inhibit cell proliferation induced by oxazolone, an unrelated contact sensitizer. The ability to DNFB tolerant cells to block afferent sensitization pathways differs from the mechanism of tolerance to picryl chloride, reported by others, where efferent pathways are blocked.     

Soluble factors in tolerance and contact sensitivity to DNFB in mice. VI. Cellular and lymphokine requirements for stimulating suppressor factor production in vitro

Coculture of spleen cells from mice tolerized with 2,4-dinitrobenzenesulfonate (DNBS) and DNP-labeled spleen cells (DNP-SC) activates Lyt-2+ T suppressor cells (Ts) to synthesize and release a suppressor factor (SSF) into the supernatant, which suppresses the transfer of contact sensitivity to DNFB. The purpose of the present study was to examine in greater detail the signals required to activate DNBS-primed Ts to produce SSF. The supernatant from cultures of tolerant cells and glutaraldehyde-fixed DNP-SC did not have SSF. In contrast, the soluble cell lysate from these cultures did contain the suppressive activity. Pretreatment of glutaraldehyde-fixed DNP-SC with either anti-DNP or anti-class I, but not anti-class II MHC, antibodies blocked SSF synthesis. The addition of IL 1 to cultures of DNBS-tolerant cells and glutaraldehyde fixed DNP-SC restored the ability of the Ts to release the synthesized factor. These results indicate that Ts recognition of the hapten/class I MHC determinant stimulates the synthesis of SSF, and a costimulator is required to induce the release of the factor. The supernatants from cultures of either L3T4-depleted tolerant cells and DNP-SC or tolerant cells and anti-I-A antibody-treated DNP-SC had no SSF activity. The addition of a costimulator (IL 1) also restored the ability of the Ts to release the synthesized factor in cultures of L3T4-depleted tolerant cells and DNP-SC. These results suggest that an L3T4 cell in the DNBS-primed cell population interacts with I-A determinants on a cell in the DNP-stimulator population to initiate the generation of the mediator required for SSF release. This further suggests that the Ts is unable to induce the costimulator from the hapten-presenting cell during interaction with the DNP/class I MHC ligand. Therefore, the production of SSF is regulated not only by the presentation of the appropriate hapten/MHC determinant but also by the interactions of cells that function in generating the costimulator needed to induce release of the suppressor factor.     

Genetic control of contract hypersensitivity. II. Suppressor cells induced by intravenous injection of DNP-coupled syngeneic spleen cells possessing thy-1 antigen, I-J determinant, Lyt-2+, 3+ antigen, FcR- and DNP-membrane binding receptor on their surfaces

The characteristics of suppressor cells induced by 2,4-dinitrophenyl (DNP)-coupled syngeneic lymphocytes (syninduced suppressor cells) were studied. 2,4-dinitro-1-fluorobenzene (DNFB) contact hypersensitivity was completely suppressed when the syninduced suppressor cells were transferred intravenously. These syninduced suppressor cells had surface markers of Thy-1, FcR^? and Lyt-2⁺, 3⁺ antigens, as well as I-J gene products on their cell surfaces. The suppression of DNFB contact hypersensitivity was abrogated when these suppressor T cells were incubated in Petri dishes coated with the DNP-syngeneic lymphoid cell membrane, which suggests that these suppressor T cells had the specific antigen-binding receptors on their cell surfaces.     

Desensitization of contact allergy to DNFB in mice. I. Description of a model system

We investigated the down-regulation of contact sensitivity (desensitization) in mice sensitized to DNFB. Mice were sensitized with DNFB, desensitized with antigen 2 wk later, and resensitized 2 wk after desensitization. Large doses of antigen (DNFB or DNBSO3) produced about 50% inhibition of the anamnestic response as measured by ear swelling after challenge with DNFB. Desensitization was antigen specific and long lasting. Lymph node cells from desensitized mice showed diminished antigen-induced proliferation in vitro. Although the anamnestic response can be inhibited by afferent- or efferent-acting suppressor cells, such suppressor cells were not demonstrated in desensitized animals. The most likely explanation is that antigen desensitizes by inactivating effector cells for contact sensitivity, although suppressor mechanisms have not been completely excluded.     

Immunopotentiating effects of amphotericin B. II. Enhanced in vitro proliferative responses of murine lymphocytes.

Enhanced in vitro proliferative responses to DNBSO3 were seen in lymph node cells and spleen cells after in vivo sensitization of mice with DNFB plus AmB compared with mice primed with DNFB alone. The T cell proliferation in the nylon column nonadherent fraction for both groups was highly similar, and the enhanced lymph node cell proliferation with AmB was demonstrated to be in the nylon adherent population consisting of both T and B cells. These and earlier studies of immunopotentiation by AmB are consistent with a mechanism that depends on selective interaction of the polyene with a subset of T cells and a resultant impairment of the normally induced suppressor regulation that limits the magnitude and duration of immune responses.     

Feedback suppression of the immune response in vivo. III. Lyt-1+ B cells are suppressor-inducer cells

We previously demonstrated that injection of a high dose (4 X 10(9] of sheep erythrocytes (SRBC) into C57BL/6 mice results in the generation of splenic B cells (plastic nonadherent, Thy-1- and Ig+) which, when transferred to normal syngeneic recipients, subsequently induce antigen-specific suppressor T cells to suppress the recipient's plaque-forming cell (PFC) responses to SRBC. In the present study we characterized the suppressor-inducer B cells phenotypically. Cytotoxic treatment of the donor's immune spleen cells with anti-Lyt-1 antibody plus complement (C'), but not with anti-Lyt-2 antibody plus C', relieved the suppression of PFC responses in recipients. The FcRr+ population separated by EA-rosette formation showed enriched suppressor-inducing activity, whereas the FcRr- population showed no activity. Our findings, taken together with the previous ones, suggest that suppressor-inducer cells are Thy-1-, Lyt-1+, Lyt-2-, FcRr+, and Ig+.     

Adsorption of a hydrophobic mutagen to five contrasting dietary fiber preparations.

The ability of five plant cell wall (dietary fiber) preparations with contrasting compositions to adsorb in vitro the hydrophobic, environmental mutagen, 1,8-dinitropyrene (DNP), was investigated. Many of the fruits and vegetables in Western diets are from dicotyledonous (broad leaved) plants and the dietary fiber from these consists mainly of unlignified cell walls. A representative of this wall type, prepared from immature cabbage leaves, showed little ability to adsorb DNP. Two other cell-wall preparations, representing lignified walls of dicotyledons and unlignified walls of vegetative parts of grasses and cereals (monocotyledons belonging to the family Poaceae), adsorbed DNP much more effectively. However, two further preparations, representing suberized walls of cork cells and lignified walls of vegetative parts of grasses and cereals, were the most effective in adsorbing DNP. Extrapolation of these data to the in vivo situation would indicate that increased consumption of the vegetative parts of grasses or cereals and plant material containing cork cells, for example potato skins, could be effective in removing hydrophobic mutagens from potential contact with colonic mucosal cells.