Suppressor T cell memory. II. The role of memory suppressor T cells in tolerance to human gamma globulin

Special regulatory T-cell review: T-cell dependent suppression revisited

The concept of T-cell dependent regulation of immune responses has been a central tenet of immunological thinking since the delineation of the two cell system in the 1960s. Indeed T-cell dependent suppression was discovered before MHC restriction. When reviewing the data from the original wave of suppression, it is intriguing to reflect not just on the decline and fall of suppressor T cells in the 1980s, but on their equally dramatic return to respectability over the past decade. Hopefully their resurgence will be supported by solid mechanistic data that will underpin their central place in our current and future understanding of the immune system. Cannon to right of them, Cannon to left of them, Cannon in front of them Volley'd and thunder'd Storm'd at with shot and shell, Boldly they rode and well, Into the jaws of Death, Into the mouth of Hell, Rode the six hundred (suppressionists). (Adapted from The Charge of the Light Brigade, Alfred, Lord Tennyson)

Induction of immune tolerance by neonatal intravenous injection of human factor VIII in murine hemophilia A

Inhibitory antibody formation is the most serious complication of factor (F)VIII replacement therapy in hemophilia A patients. FVIII-deficient mice were used to study new approaches for induction of immune tolerance. Neither antiFVIII inhibitory antibodies nor antiFVIII IgGs were observed in 13 of 14 adult mice that received 0.05 U g(-1) body weight of human FVIII intravenously within 24 h after birth and repeated injections as adults. In contrast, high FVIII antibody titers (>50 Bethesda Units mL(-1)) developed in seven of 13 mice injected on day 3 postpartum and in all adult mice not treated neonatally. One of nine mice and three of 17 mice developed high-titer antiFVIII inhibitory antibody when they were treated initially with 2-fold (0.1 U g(-1) body weight) and 10-fold higher doses (0.5 U g(-1) body weight) FVIII on day 0, respectively. A human FVIII-specific T-cell proliferative response was absent in splenocytes from neonatally treated mice. The tolerance was FVIII specific because antitoxoid antibodies developed after immunization with tetanus toxoid. Splenocytes failed to proliferate or produce interferon (IFN)-gamma in response to FVIII stimulation, yet still secreted interleukin-2. A proliferative response was restored with exogenous IFN-gamma or interleukin-12, suggesting that lack of inhibitor to FVIII was due to IFN-gamma-dependent anergy. Thus, exposure on day 0 to physiological levels of FVIII antigen might be important for induction of immune tolerance. This immune tolerance model may provide a basis for new approaches to prevention of FVIII inhibitors during replacement therapy.

Neonatal peptide exposure can prime T cells and, upon subsequent immunization, induce their immune deviation: implications for antibody vs. T cell-mediated autoimmunity

Neonatal exposure to antigen is believed to result in T cell clonal inactivation or deletion. Here we report that, contrary to this notion, neonatal injection of BALB/c mice with a hen egg lysozyme peptide 106-116 in putative "tolergenic" doses induced a T cell proliferative and an immunoglobulin G (IgG) antibody (Ab) response of both T helper cell 1 (Th1)- (IgG2a, IgG2b, and IgG 3) and Th2-dependent (IgG1) isotopes. Upon subsequent challenge with the peptide in complete Freund's adjuvant in adult life, although this neonatal regimen suppressed proliferation and the production of Th1 cytokines (interleukin[IL]-2 and interferon gamma), Th2 cytokine (IL-5, IL-4, and IL-10) secretion was increased, and the serum levels of Th1- and Th2-dependent isotypes of peptide-specific Ab remained elevated. The in vitro proliferative unresponsiveness in Th1 cells could be reversed by Abs to Th2 cytokines (IL-4 and IL-10). Thus, neonatal treatment with a peptide antigen induces T cell priming including production of IgG Abs of both Th1- and Th2-dependent isotypes. Upon subsequent peptide exposure, the peptide-specific T cell responses undergo an effective class switch in the direction of Th2, resulting in T cell proliferative unresponsiveness. Accordingly, this shift towards increased Ab production to autoantigen could be deleterious in individuals prone to antibody-mediated diseases. Indeed, neonatal treatment with a self-autoantigenic peptide from an anti-DNA monoclonal Ab (A6H 58-69) significantly increased the IgG anti-double-stranded DNA Ab levels in lupus-prone NZB/NZW F1 mice, despite suppressing peptide-specific T cell proliferation. This adverse clinical response is in sharp contrast to the beneficial outcome of neonatal treatment with autoantigens in Th1-mediated autoimmune diseases, such as autoimmune encephalomyelitis, as reported by others. A Th1 to Th2 immune deviation can explain the discordant biological responses after the presumed induction of neonatal tolerance in autoantibody- vs. Th-1 mediated autoimmune diseases.

Mechanisms in CD4 antibody-mediated transplantation tolerance: kinetics of induction, antigen dependency and role of regulatory T cells

CBA/Ca mice may be made tolerant to minor histoincompatible B10.BR skin grafts by treatment with a short course of non-depleting anti-mouse CD4 and CD8 monoclonal antibodies (mAb), during the transplantation period. We wished to determine when, in relation to antibody therapy, the T cells became tolerant. This was investigated by a series of adoptive transfer experiments in which mAb-treated cells were removed from therapeutic antibody at defined times after skin grafting, and exposed to fresh antigen in the absence of further mAb treatment. We show here that T cells do not become fully tolerant until 5 weeks after skin grafting. If antibody therapy is continued for the full 5 weeks, T cell tolerance can still be established, suggesting that antibody therapy does not prevent lymphocytes from registering the presence of antigen. Once the tolerant state is established, it is difficult to break that tolerance by lymphocyte infusions from normal donors. This "resistance" is mediated by T cells of the tolerant host. We show that the maintenance of both tolerance and "resistance" requires a continuous supply of antigen. When tolerant cells were "parked" in T cell-depleted mice, tolerance and "resistance" were eventually lost by 6 months. In contrast, "parked" cells exposed to fresh antigen at any time up to 4 months remained tolerant and "resistant" indefinitely. Finally, we wished to establish whether "resistance" was peculiar to this form of peripheral tolerance, or whether it might also be present in tolerance considered to be classically central. We observed resistance to be greater in the mAb-treated peripherally tolerant group, but noted that some of the centrally tolerant animals also exhibited a level of resistance above that of T cell-ablated controls. This suggests that a tolerance mechanism whose role is only minor in central tolerance may have a major role in antibody-mediated peripheral tolerance.

Immune deviation in the mouse: transfer of selective depression of the contact sensitivity and interleukin-2 response with retention of interferon-gamma production requires CD8+ T cells

Mice were injected intravenously (i.v.) with trinitrophenyl (TNP)-modified spleen cells. They were subsequently immunized by epicutaneous application of 2,4,6-trinitrochlorobenzene (TNCB, picryl chloride) or 'oxazolone'. The intravenous injection of antigen caused immune deviation (split tolerance) with selective loss of contact sensitivity (CS) and antigen-induced interleukin-2 (IL-2) production, and concomitant retention of antigen-induced interferon-gamma (IFN-gamma) production. This phenomenon was antigen specific as the response to oxazolone was unaffected. Moreover, lymph-node cells stimulated with antigen three times in vitro (from 'deviated' mice which had been injected with antigen i.v., and then sensitized with TNCB) showed limited proliferation. The per cent of IL-2R+ cells and the absolute number of V beta 8+ cells dropped. In contrast, lymph-node cells from 'undeviated' mice showed increased proliferation and IL-2 production on repeated stimulation with antigen in vitro and the per cent of IL-2R+ cells and the absolute number of V beta 8+ cells recovered increased. Spleen cells, taken from mice 3-7 days after the injection of antigen i.v., transferred immune deviation to normal recipients i.e. following epicutaneous immunization with TNCB, the recipients showed the same selective unresponsiveness as the donors. Thy-1+ CD4- CD8+ cells were required. These findings indicate that immune deviation can be demonstrated at the level of lymphokine production.

Bovine gamma globulin-specific CD4+ T cells are retained by bovine gamma-globulin-tolerant mice

Immunological tolerance is an acquired state of antigen-specific nonresponsiveness which is generally attributed to either the deletion or suppression of tolerogen-specific T helper cell clones. Unresponsiveness to xenogeneic immunoglobulins can be readily induced and has been extensively studied in order to ascertain the means by which tolerance is established and maintained. As an absence of reactivity to foreign immunoglobulin has been noted in situations where suppressor cell activity was minimized, this tolerant state has often been ascribed to clonal deletion. The present study demonstrates that bovine gamma-globulin (BGG)-tolerant mice are unable to generate humoral responses to BGG in vivo and yet harbor BGG-specific CD4+CD8- T cells which can divide and secrete interleukin 2 when stimulated in vitro. Indeed, the in vitro reactivity to BGG of these cells exceeded that of a similar population of non-immune cells. This is in direct opposition to the loss of response that would be expected if clonal deletion were operative. The presence of BGG-specific CD4+ T cells, which appear to be at least partly primed, in mice unresponsive to BGG, indicates that tolerance to BGG is likely to be dependent on unidentified immunoregulatory processes rather than clonal deletion.

Network regulation of autoimmunity: an automation model

Four classes of regulatory T lymphocytes have been implicated in the control of experimental autoimmune diseases: a pair of helper and suppressor T lymphocytes that recognize the self-antigen (antigen-specific); and a pair of helper and suppressor T lymphocytes that recognize the autoimmune effector lymphocytes (anti-idiotypic). The anti-idiotypic pair of regulators was detected following vaccination against autoimmune disease using autoimmune effector T clones as vaccines. To learn how the anti-idiotypic regulatory lymphocytes might function in concert with the antigen-specific regulatory lymphocytes, we devised a network in which the cell populations could be viewed as interconnected automata. Analysis of this novel network model suggests how self-tolerance may operate, how progressive autoimmune disease may develop, and how T-cell vaccination can control autoimmune disease.

Suppression of antigraft immunity by preimmunization. V. Characterization of suppressor T memory cells

We have previously shown that after intravenous (i.v.) immunization of mice with allogeneic spleen cells, two populations of suppressor T (Ts) cells may occur that can suppress delayed-type hypersensitivity (DTH) to alloantigens: Ts effector cells that transiently occur in the spleen, and long-lived, recirculating Ts cells that occur in thoracic duct lymph and can be transferred by parabiosis. In this study, we investigated whether the latter Ts cells fulfill the criteria for memory T lymphocytes, such as induction by doses of antigen lower than required for T effector cell induction, accelerated onset of activity after reactivation and an increased activity as compared with virgin T cells. The Ts cells accounting for the long-lasting state of suppression of DTH to alloantigens indeed fulfilled these criteria. These Ts memory cells displayed the Thy-1+, L3T4-, Lyt-1+2+ phenotype.

Effect of neonatal thymectomy on experimental autoimmune hepatitis in mice

Using an autoimmune hepatitis model of A/J mice which was prepared with immunization by syngeneic crude liver proteins, various influences of neonatal thymectomy were studied by observations of histological liver changes, autoantibody to liver-specific membrane lipoprotein (LSP), delayed-type hypersensitivity (DTH) to LSP, and purified protein derivative (PPD), and suppressor activity to LSP. The liver changes in the thymectomized mice were more intense than those in the non-thymectomized controls. Production of the anti-LSP autoantibodies and positive DTH to syngeneic LSP could be recognized in both groups of the thymectomized mice and the non-thymectomized controls, but the levels of those were higher in the former. In the level of DTH to PPD the thymectomized mice were lower than the non-thymectomized controls. Adoptive transfer experiments showed that suppressor activity to LSP was reduced in the spleen cells of neonatally thymectomized mice. This experiment suggests that neonatal thymectomy is apt to abolish tolerance to LSP on account of depressed suppressor activity to autoantigen, and accordingly liver damage is increased.

Mice naturally tolerant to C5 have T cells that suppress the response to this antigen

We examined whether C5-sufficient mice which are naturally tolerant to this antigen have suppressor T cells to C5 humoral immune response. Two congenic strains of mice B10.D2 (NSN) and B10.D2 (OSN) differing only in the presence or absence of C5 were used. Irradiated (760 rds) sufficient hosts were reconstituted with a nonadherent spleen cell suspension from either sufficient or deficient mice or a mixture of both. Hemolytic C5 levels were assayed. Sufficient spleen cells appeared to prevent the drop of C5 level caused by anti-C5 antibody made by deficient spleen cells. Spleen cell suspensions from sufficient mice primed with deficient spleen cells exhibited better anti-C5 activity than normal sufficient spleen cell suspensions. This anti-C5 activity is abrogated by treatment of the NSN spleen cell suspensions obtained from NSN primed with OSN spleen cells with anti-Thy-1.2 antiserum and complement. Suppression of the humoral response to C5 failed to affect the anti-sheep red blood cell immune response. Suppressor T cells are resistant to low-dose irradiation, cortisone treatment and adult thymectomy. In contrast, they are sensitive to high doses of irradiation and both high and low doses of cyclophosphamide treatment. Thus, C5-sufficient mice, in contrast to C5-deficient mice, appear to have antigen-specific suppressor T cells which downregulate the humoral immune response to C5. In addition, we examined the relationship of these suppressor T cells to the state of tolerance in helper T cells of C5-sufficient mice. This was done in irradiated deficient mice which were repopulated with spleen cell suspensions selectively depleted of either Lyt-1+ or Lyt-2+ T cell subsets. These chimeras were challenged with murine C5 and both the primary and secondary immune response was measured by inhibition of the C5 hemolytic activity. It was found that only spleen cell suspensions of the deficient mice selectively depleted from the Lyt-2+ subset of T cells responded to the antigen both in the primary and secondary response. In contrast, either subset of T cells from the sufficient mice failed to respond. Thus, it appears that in sufficient mice helper T cells to C5 are intrinsically tolerant or physically and/or functionally deleted. In conclusion, the data suggest that both T cell compartments are unresponsive and play a role in the mechanism of tolerance to a physiologic antigen.

Induction of tolerance to one determinant on a synthetic peptide does not affect the response to a second linked determinant. Implications for the mechanism of neonatal tolerance induction

To investigate the mechanism underlying neonatal T cell tolerance, we used synthetic peptides to induce tolerance. We found that induction of tolerance to one determinant on a 23-amino acid peptide did not affect the response to an adjacent determinant on the same peptide. There was no evidence of suppression of the response to the second determinant. Furthermore, even small peptides near the minimal size for a determinant, which would be very unlikely to possess a suppressor T cell-inducing determinant as well as a proliferative T cell-inducing determinant, could induce tolerance. These studies provide in vivo experiments supporting clonal inactivation as the mechanism of neonatal tolerance to immunogenic peptides.

The use of tolerization in the production of monoclonal antibodies against minor antigenic determinants

An initial attempt to prepare monoclonal antibodies specific for the Dictyostelium discoideum lysosomal enzyme beta-glucosidase was unsuccessful. All of the antibodies resulting from this fusion recognized an extremely immunogenic epitope that is present on all of the lysosomal enzymes of Dictyostelium. In two succeeding fusions, changes in the immunization schedule intended to increase the immune response to enzyme-specific epitopes were not entirely successful. Although nine hybridomas producing antibodies specific for beta-glucosidase resulted from these two fusions, most (70%) of the cell lines isolated secrete antibodies that recognize the shared, immunodominant epitope. Moreover, the nine beta-glucosidase-specific antibodies proved to be of limited utility since none recognize the native enzyme. Therefore, we attempted to tolerize a BALB/c mouse to the common epitope by injecting the lysosomal enzyme, N-acetylglucosaminidase, within 40 h after birth. As an adult, this animal was immunized with beta-glucosidase. Fusion of the spleen cells from this mouse with myeloma cells resulted in the isolation of nine hybridoma lines that produce antibodies specific for beta-glucosidase. No antibodies reactive with the common epitope were detected. These results suggest that tolerization may provide a means whereby an undesired class of antibody-producing cell lines can be selectively eliminated from the products of a fusion.

Isoelectric focusing spectra of anti-bacterial alpha-amylase antibody unique for antigen-induced suppression

The effect of intravenous (i.v.) administration of bacterial alpha-amylase (B alpha A) on the IgG antibody response to a subsequent challenge with B alpha A in incomplete Freund's adjuvant (IFA) varied with the difference in responsiveness of the parental strains. High-responder C3H/He (C3) mice given injections of either 200 or 4 micrograms of B alpha A, which alone were unable to trigger a detectable IgG antibody response, generated an enhanced response to an immunogenic challenge given 25 days after the last i.v. injection. The response of low-responder C57BL/6 (B6) mice previously exposed to B alpha A, following a different kinetic course depending on the exposing dose, reached a plateau lower than the levels of control responses (tentatively designated as high- and low-zone suppression). Prior exposure of (B6 X C3)F1 hybrids to 200 micrograms led to the enhanced response, whereas pretreatment with 4 micrograms rendered them partially tolerant to a subsequent challenge. These results suggest that the capacity to achieve low-zone suppression is inherited as a dominant trait. Isoelectric focusing (IEF) analysis revealed that these enhanced responses expanded antibody heterogeneity in a strictly restricted, strain-specific manner as observed during the normal antibody response, although the rate of expansion was accelerated. The specific antibodies produced by individual high-zone suppressed B6 mice were focused as a limited set of bands in a narrow pH range where the specific antibodies produced early in the normal response were focused. In contrast, the response of low-zone suppressed B6 and F1 hybrid mice was characterized by a unique process of heterogeneity expansion.

Neonatal T-cell tolerance to minimal immunogenic peptides is caused by clonal inactivation

The mechanisms underlying T-lymphocyte tolerance induced in neonatal mice are still unknown. It is unclear whether the tolerant state is the result of inactivation of T cells on exposure to antigen during development or of active suppression by other T cells specific for the same antigen. To distinguish between these two hypotheses, we have analysed the specificity of tolerance to three cytochrome peptides which differ by only a single amino-acid substitution in the epitope recognized by proliferative T cells. The peptides stimulate proliferative responses which are highly specific with minimal cross-reactivity. As antigen-induced clonal inactivation would address the same cells normally activated by that antigen, the specificity of tolerance should exactly match that of the proliferative response to the antigen, and each cytochrome peptide should induce tolerance to itself alone. Conversely, as T-suppressor (Ts) and T-proliferative (Tp) cells almost invariably seem to recognize distinct, non-overlapping determinants on protein antigens, suppressor-mediated tolerance should not be affected by substitutions in the proliferative T-cell epitope. Tolerance would depend solely on the existence of a shared suppressor determinant, so each cytochrome peptide should induce cross-tolerance to the others. We found that the specificity of tolerance matched that of the proliferative response: each peptide induced tolerance for itself but the response to the variants was unaltered. This result strongly supports the hypothesis of clonal inactivation as an important mechanism in induction of neonatal tolerance.

A tumor immunotherapy technique based on modulation of the idiotype anti-idiotype network

In this communication I propose a technique for manipulating the idiotype anti-idiotype network with the aim of enhancing the immune response to tumors. The theoretical basis for this technique follows from Jerne's network theory of the immune system. By tolerizing the host to immunoglobulin bearing idiotypes directed against tumor associated antigens it should be possible to dampen the expected anti-idiotype response to these idiotypes. A reduced anti-idiotype response should result in an increased idiotype response and thus a greater anti-tumor immune response.

A role for suppressor T cells in induction of self-tolerance

The potential role of suppressor T cells (Ts) in the induction of self-tolerance was investigated by eliminating I-J+ cells during ontogeny (I-J antigens are encoded by the I-J subregion of the murine major histocompatibility complex). To achieve this, F1 mice were exposed to anti-I-J antibodies via the transplacental route by mating B10.A(3R) females, preimmunized with B10.A(5R) cells, with CBA males. At 6 weeks of age, the offspring were injected with rat erythrocytes (RRBC) to induce erythrocyte autoantibodies. By comparison with age-matched controls, Ts-depleted mice produced significantly higher titers of autoantibody, whereas there was no difference in the antibody response of the two groups to the foreign determinants on the RRBC. The selective increase in autoantibody production was mirrored at the clonal level by the appearance of self-reactive B-cell hybridomas after fusion of RRBC-immune spleen cells with the NS-1 cell line. On the other hand, when helper cell function of RRBC-primed cells was measured in a T-cell proliferative assay, Ts depletion in utero resulted in enhanced T-cell activity to nonself (RRBC) but not to self (mouse erythrocyte) determinants. Thus, helper T cells recognizing nonself determinants on RRBC appeared to be responsible for activating self-specific B cells, presumably through linked recognition of different epitopes on mouse erythrocytes. Taken together, these findings indicate that elimination of I-J+ cells during ontogeny can lead to the appearance and activation of "forbidden" B-cell clones and points to a central role for Ts in induction as well as maintenance of self-tolerance.

Induction of suppressor cells by a tumor-derived suppressor factor

Murine fibrosarcomas produce a factor that activates suppressor cells to inhibit expression of delayed-type hypersensitivity (DTH) responses to dinitrochlorobenzene (DNCB). This tumor-derived suppressor factor (TDSF) was partially purified by preparative isoelectric focusing of spent medium and 3 M KCl extracts of cultured methylcholanthrene-induced and spontaneous fibrosarcomas of C3H/He mice. Incubation of 1 micrograms/ml of a fraction, isoelectric pH less than 2.9, with normal syngeneic spleen cells for 1-6 hr at 37 degrees C induced suppressor cells that inhibited the primary DTH response to DNCB upon intraperitoneal transfer to normal C3H/HeJ mice. TDSF was not present in extracts of either syngeneic embryonic fibroblasts or normal spleen cells or in medium conditioned by normal peritoneal exudate cells but was present in 3 M KCl extracts of and the spent medium from four different cultured murine fibrosarcomas. TDSF activity was not restricted at the major histocompatibility complex. The suppressor cells inhibited the efferent limb of the DTH response because (1) hyporesponsive recipients of TDSF-treated spleen cells had splenic effector T cells capable of transferring DTH to DNCB into naive secondary recipients and (2) the ability of Lyt 1+,2- effector Tdth cells to transfer a secondary DTH response to DNCB was inhibited by co-incubation with macrophages or Lyt 1-,2+ T cells treated with TDSF. Preliminary biochemical analysis suggested that TDSF was an RNA- protein complex. Thus, several murine fibrosarcomas produced a soluble factor that activated splenic suppressor cells to depress the immune response to nonneoplastic antigens. These suppressor factors represent a novel group of regulatory molecules which may be ribonucleoprotein complexes.

Antigen induces chronic idiotype suppression

Hapten coupled to isologous gamma globulin can substitute for anti-idiotypic antibody in the induction of neonatal chronic idiotype suppression. The immunologically suppressed animals fail to express an idiotypically defined subset of anti-hapten antibodies in later life and harbor regulatory T cells that prevent the expression of this same antibody subset by B cells. Suppression ceases after several months, but memory of suppression persists and can be recalled by small doses of hapten-carrier conjugate. These data show that an antigen present in a mouse at birth is able to generate a T-cell-dependent suppressive mechanism that controls expression of antigen-specific antibodies through the recognition of antibody idiotypes. The idiotypic network is thus involved in the control of tolerance and the available antibody repertoire.

Antigen-specific suppression of anti-influenza antibody production in man. Possible role of a membrane-antigen complex

E rosette-forming (E+) cells from human secondary lymphoid tissue were incubated with high dose influenza A virus (Mem-Bel) in an attempt to generate suppressor T cells. Suppression was assayed by transferring the antigen-pulsed E+ cells into effector cultures consisting of E+ and E- cells stimulated with immunogenic amounts of either the inducing virus Mem-Bel) or the non-cross-reacting influenza B virus (B/HK). The transfer resulted in marked inhibition of IgG, IgA and IgM antibody production to Mem-Bel but not to the control antigen, B/HK virus. The suppressive effect was specific at the level of induction as well as expression since E+ cells exposed to high dose Mem-Bel could provide help to an effector culture containing E- cells and optimal dose of B/HK virus. However, metabolically active cells did not appear to be required for suppression. Thus, it could be elicited (a) after only 15 min incubation of E+ cells with high-dose virus and (b) by E+ cells exposed to irradiation, incubated in the presence of metabolic inhibitors, or disrupted by repeated freeze thawing. In contrast, treatment of E+ cells with pronase reversed the suppressive effect. Interestingly, virus heated to 70 degree C failed to induced suppression, while retailing the ability to elicit a normal helper response. Suppression induced by exposure to standard amounts of high-dose antigen was mediated by T cells of both helper/inducer (Leu-3a+) and suppressor/cytotoxic subsets (Leu-2a+), but not by B cells. Two groups of observations pointed to the B cell as the target of suppression. First, suppression could still be transferred to effector cultures in which helper T cells had been replaced by T cell-replacing factor or suppressor T cells removed by irradiation. Second, significant inhibition of antibody production was obtained when the transfer of antigen-pulsed E+ cells was delayed for up to 120 h after initiation of the effector culture. Taken together the results suggest that suppression in this system is due to the formation of an antigen bridge between specific receptor sites on the T cell membrane and the target. Although not dependent on triggering of metabolically active suppressor T cells the phenomenon highlights the need for care in interpreting the mechanism of suppression by high-dose antigen and could, in addition, represent a biologically important control mechanism capable of rapid inhibition of effector T cells and B cells in sites of high antigen concentration.

The long-lasting state of specific nonresponsiveness induced by intravenous immunization with alloantigens is due to the generation of recirculating suppressor T cells

We investigated whether the long-lasting state of nonresponsiveness that is induced by intravenous immunization with alloantigens is mediated by suppressor T cells, or is caused by inactivation or deletion of the relevant alloreactive T cell clones. The data from parabiosis and thoracic duct drainage experiments suggest that the state of nonresponsiveness depends on recirculating non-proliferating Ts memory cells.

Autoantibody to liver-specific lipoprotein in the mouse: regulation by naturally occurring autoantigen specific suppressor cells

Indirect and direct evidence is presented that normal, non-immune mice have cells which suppress antibody production to murine liver specific lipoprotein (LSP) autoantigens with little or no effect on the response to a closely related foreign antigen complex, rabbit LSP. Suppressor control mechanisms were suggested in low responder BALB/c mice which produced LSP autoantibody only after exposure to low dose X-irradiation or treatment with cyclophosphamide. Adoptive transfer experiments in X-irradiated BALB/c mice and untreated C57BL/6 mice showed that cells from normal mouse spleen prevented LSP autoantibody production when put into the circulation of mice prior to immunization with foreign rabbit LSP. This suppressor activity was destroyed by treatment with antisera to T cells and by low dose X-irradiation. The normal spleen cells were ineffective as suppressors if given after primary immunization with rabbit LSP had commenced. It is suggested that the adoptive transfer of normal spleen cells prior to immunization with foreign LSP supplements homeostatic mechanisms in favour of tolerance to LSP autoantigen. It is argued that the LSP autoantibody response in the mouse is a unique model for the study of autoantigen specific naturally occurring suppression.

Specificity, duration and mechanism of idiotype suppression induced by neonatal injection of monoclonal anti-idiotope antibodies into mice

Monoclonal antibodies detecting idiotopes on the germ line-encoded anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibody B1-8 were injected at various doses into newborn mice and the expression of B1-8 idiotopes was measured in anti-NP responses in later life. Suppression was long lasting, and a 100-fold increase in the dose of anti-idiotope delayed recovery from suppression by 5-6 weeks. Upon injection of a single anti-idiotope, suppression was observed for all B1-8 idiotopes to various degrees. Certain idiotopically defined antibody phenotypes were much more efficiently suppressed, and later recovered from suppression, than others. This specificity pattern was observed at the level of both B and T cells from the manipulated animals, as demonstrated in cell transfer experiments in which such cells were mixed with normal T and B cells. In these experiments, there was evidence for suppression mediated by regulatory T (and possibly also B) cells. Whereas the B cells from the manipulated animals were idiotypically unresponsive in a T cell-dependent adoptive primary response, the frequency of lipopolysaccharide-reactive B cells expressing the target idiotype was only slightly reduced in these animals as compared to control mice. Together with data on the elimination of anti-idiotope antibody from the neonatally injected animals these results are interpreted in the following way: idiotype suppression is induced through the reaction of anti-idiotope with idiotopes expressed on the surface of newly generated B cells, at microgram concentrations of anti-idiotope. When the concentration of anti-idiotope fall below that level, recovery from suppression sets in. Two types of suppression are induced. The first, namely, direct blockade of B cell maturation, is short-lived. The second involves the induction of regulatory cells, perhaps through idiotope-bearing antibody V regions complexed by anti-idiotope. This type of suppression is long-lived and its specificity depends upon the distribution of the target idiotope in the antibody repertoire and/or peculiarities of the T cell receptor repertoire. It impinges on the selection of the B cell repertoire in the animal as expressed in T cell-dependent (and possibly other) responses and is thus hardly seen at the level of lipopolysaccharide-reactive (immature) cells. Idiotype suppression by regulatory cells may be perpetuated by antigen interacting with idiotypic antibodies on the B cell surface and may therefore play a role in establishing tolerance not only for the expressed antibody repertoire, but for self antigens in general.

Generation and decay of the immune response to a progressive fibrosarcoma. II. Failure to demonstrate postexcision immunity after the onset of T cell-mediated suppression of immunity

This study shows that surgical removal of the meth A fibrosarcoma from its semisyngeneic host fails to result in postexcision immunity to growth of a tumor implant unless the host already has acquired a mechanism of concomitant immunity to growth of an implant. Therefore, tumor excision does not cause immunity to be generated but preserves a mechanism of concomitant immunity that already exists and which otherwise would eventually undergo down-regulation under the influence of suppressor T cells. Removal of the tumor after it has grown large enough to cause the T cell-mediated suppression of concomitant immunity does not result in the reemergence of immunity. Instead, the host remains unable to generate concomitant immunity to a second tumor for a long period of time and retains, for at least 31 d, suppressor T cells able to passively transfer suppression to appropriate recipients. Like the suppressor T cells responsible for active suppression of concomitant immunity, the suppressor T cells responsible for "memory" suppression are of the Ly-1+2- phenotype. The results indicate that progressive tumor growth results in a state of immunological tolerance of tumor-specific, transplantation antigens that can persist in the apparent absence of tumor antigens.

Induction of memory and effector suppressor T cells by perinatal exposure to antigen

The development of tolerance and suppression after perinatal exposure to antigen was studied to clarify the role of suppressor cells in self tolerance. Deaggregated human gamma globulin (dHGG) was administered transplacentally to fetal mice by injecting their mothers at various stages of pregnancy. Other mice were exposed to dHGG present in the colostrum of foster mothers previously injected with dHGG. Nonspecific suppression was seen on adoptive transfer of spleen cells from all donors less than six weeks of age. After that time, HGG-specific primary suppression by Ly-1-2,3+Ia+ T cells was detected in all animals exposed to dHGG either pre- or postnatally and persisted for up to three months. In addition, recall of specific memory suppression by antigen challenge was demonstrable for up to six months. Tolerance, on the other hand, was generated only by higher doses of dHGG in utero and was relatively short-lived when compared to suppression. The short duration of tolerance could not be attributed to the generation of T helper cells, since no significant HGG-specific helper activity was detected after perinatal exposure to HGG; rather it was thought to be due to the failure of small doses of dHGG to generate sufficient effector T suppressor (Ts) cells to inactivate the continually increasing number of HGG-specific B cells being generated during ontogeny. Since perinatal tolerance to HGG is known to be prolonged by repeated exposure to antigen, this model implies that the maintenance of natural self tolerance is Ts cell dependent and requires the continued presence of antigen.

Absence of suppression in natural and induced tolerance to F antigen

The role of suppression in natural and induced tolerance to F antigen was investigated in two sets of experiments. In the first, CBA mice were submitted to pretreatments which decrease suppression and the antibody response to self- or allo-F type was investigated. The second set of experiments involved the transfer of spleen cells from tolerized or from naturally tolerant mice into normal mice which were then primed with allo-F, as well as the co-transfer of tolerant and primed lymphocytes into normal mice, to test whether tolerant lymphocytes present suppressor cells. The results indicate that the immune response against allo-F antigen is normally kept in a low level by a suppressive mechanism, and that F-specific suppressor T cells are absent from tolerant mice.