Oral tolerance to nickel requires CD4+ invariant NKT cells for the infectious spread of tolerance and the induction of specific regulatory T cells

Previously, oral administration of nickel to C57BL/6 wild-type (WT) mice was shown to render both their splenic T cells and APCs (i.e., T cell-depleted spleen cells) capable of transferring nickel tolerance to naive syngeneic recipients. Moreover, sequential adoptive transfer experiments revealed that on transfer of tolerogenic APCs and immunization, the naive T cells of the recipients differentiated into regulatory T (Treg) cells. Here, we demonstrate that after oral nickel treatment Jalpha18(-/-) mice, which lack invariant NKT (iNKT) cells, were not tolerized and failed to generate Treg cells. However, transfer of APCs from those Jalpha18(-/-) mice did tolerize WT recipients. Hence, during oral nickel administration, tolerogenic APCs are generated that require iNKT cell help for the induction of Treg cells. To obtain this help, the tolerogenic APCs must address the iNKT cells in a CD1-restricted manner. When Jalpha18(-/-) mice were used as recipients of cells from orally tolerized WT donors, the WT Treg cells transferred the tolerance, whereas WT APCs failed to do so, although they proved tolerogenic on transfer to WT recipients. However, Jalpha18(-/-) recipients did become susceptible to the tolerogenicity of transferred WT APCs when they were reconstituted with IL-4- and IL-10-producing CD4(+) iNKT cells. We conclude that CD4(+) iNKT cells are required for the induction of oral nickel tolerance and, in particular, for the infectious spread of tolerance from APCs to T cells. Once induced, these Treg cells, however, can act independently of iNKT cells.     

Tolerance to nickel: oral nickel administration induces a high frequency of anergic T cells with persistent suppressor activity.

We adapted our mouse model of allergic contact hypersensitivity to nickel for the study of tolerance. Sensitization in this model is achieved by the administration of nickel ions with H(2)O(2); nickel ions alone are unable to prime naive T cells, but can restimulate primed ones. A 4-wk course of oral or i.p. administration of 10 mM NiCl(2) to naive mice induced tolerance, preventing the induction of hypersensitivity for at least 20 wk; long term desensitization of nickel-sensitized mice, however, required continuous NiCl(2) administration. When splenic T cells of orally tolerized donors, even after a treatment-free interval of 20 wk, were transferred to naive recipients, as with lymph node cells (LNC), they specifically prevented sensitization of the recipients. The LNC of such donors were anergic, because upon in vivo sensitization with NiCl(2) in H(2)O(2) and in vitro restimulation with NiCl(2), they failed to show the enhanced proliferation and IL-2 production as seen with LNC of mice not tolerized before sensitization. As few as 10(2) bulk T cells, consisting of both CD4(+) and CD8(+) cells, were able to specifically transfer tolerance to nickel. A hypothesis is provided to account for this extraordinarily high frequency of nickel-reactive, suppressive T cells; it takes into account that nickel ions fail to act as classical haptens, but form versatile, unstable metal-protein and metal-peptide complexes. Furthermore, a powerful amplification mechanism, such as infectious tolerance, must operate which allows but a few donor T cells to tolerize the recipient.     

Effector CD4 cells are tolerized upon exposure to parenchymal self-antigen

It has long been established that exposure of naive T cells to specific Ag in the absence of adjuvant leads to tolerization. Nonetheless, the potential of effector CD4 cells to be tolerized has been less well characterized. To address this issue, we have used an adoptive transfer system in which naive TCR transgenic hemagglutinin (HA)-specific CD4(+) T cells are initially primed to express effector function upon exposure to an immunogenic recombinant vaccinia virus expressing HA, and then exposed to forms of HA that are tolerogenic for naive CD4 cells. HA-specific effector CD4 cells residing in both the spleen as well as in two separate nonlymphoid tissues were tolerized upon exposure to high doses of exogenous soluble HA peptide. Additionally, tolerance could also be induced by bone marrow-derived APCs that cross-present parenchymally derived self-HA. Thus, effector CD4 cells are susceptible to similar tolerogenic stimuli as are naive CD4 cells.     

Orally tolerized T cells can form conjugates with APCs but are defective in immunological synapse formation

Oral tolerance is systemic immune hyporesponsiveness induced by the oral administration of soluble Ags. Hyporesponsiveness of Ag-specific CD4 T cells is responsible for this phenomenon. However, the molecular mechanisms underlying the hyporesponsive state of these T cells are not fully understood. In the present study, we investigated the ability of orally tolerized T cells to form conjugates with Ag-bearing APCs and to translocate TCR, protein kinase C-theta (PKC-theta), and lipid rafts into the interface between T cells and APCs. Orally tolerized T cells were prepared from the spleens of OVA-fed DO11.10 mice. Interestingly, the orally tolerized T cells did not show any impairment in the formation of conjugates with APCs. The conjugates were formed in a LFA-1-dependent manner. Upon antigenic stimulation, the tolerized T cells could indeed activate Rap1, which is critical for LFA-1 activation and thus cell adhesion. However, orally tolerized T cells showed defects in the translocation of TCR, PKC-theta, and lipid rafts into the interface between T cells and APCs. Translocation of TCR and PKC-theta to lipid raft fractions upon antigenic stimulation was also impaired in the tolerized T cells. Ag-induced activation of Vav, Rac1, and cdc42, which are essential for immunological synapse and raft aggregation, were down-regulated in orally tolerized T cells. These results demonstrate that orally tolerized T cells can respond to specific Ags in terms of conjugate formation but not with appropriate immunological synapse formation. This may account for the hyporesponsive state of orally tolerized T cells.     

Regulatory T cells maintain long-term tolerance to myelin basic protein by inducing a novel, dynamic state of T cell tolerance

The pathogenesis of multiple sclerosis involves a breakdown in T cell tolerance to myelin proteins like myelin basic protein (MBP). Most MBP-specific T cells are eliminated by central tolerance in adult mice, however, the developmentally regulated expression of MBP allows MBP-specific thymocytes in young mice to escape negative selection. It is not known how these T cells that encounter MBP for the first time in the periphery are regulated. We show that naive MBP-specific T cells transferred into T cell-deficient mice induce severe autoimmunity. Regulatory T cells prevent disease, however, suppression of the newly transferred MBP-specific T cells is abrogated by activating APCs in vivo. Without APC activation, MBP-specific T cells persist in the periphery of protected mice but do not become anergic, raising the question of how long-term tolerance can be maintained if APCs presenting endogenous MBP become activated. Our results demonstrate that regulatory T cells induce naive MBP-specific T cells responding to nonactivated APCs to differentiate into a unique, tolerized state with the ability to produce IL-10 and TGF-beta1 in response to activated, but not nonactivated, APCs presenting MBP. This tolerant response depends on continuous activity of regulatory T cells because, in their absence, these uniquely tolerized MBP-specific T cells can again induce autoimmunity.     

Immune suppression in vivo with antigen-modified syngeneic cells. II. T cell-mediated nonresponsiveness to fowl gamma-globulin.

Intravenous administration of syngeneic spleen cells coupled with the palmitoyl derivative of fowl gammma-globulin (p-F gamma G) results in a profound state of F gamma G-specific tolerance in C57BL/6 mice. Administration of p-F gamma G coupled syngeneic cells specifically reduces both the primary and secondary hapten and carrier-specific PFC responses to TNP-F gamma G. Since the haptenic response is affected, the tolerance functions at the level of the F gamma G-specific helper T cell. As few as 10(3) p-F gamma G spleen cells carrying only 1 ng of p-F gamma G can induce tolerance. At least a 2-day-induction period is required. This nonresponsiveness is long lived, lasting over 120 days. Spleen cells from tolerized mice can transfer suppression to normal syngeneic recipients. Treatment of tolerant spleens with anti-Thy 1.2 antiserum + C eliminates the suppressor cell activity. In addition, thymocytes and purified splenic T cells from tolerized mice can transfer suppression to normal recipients. Thus, at least a component of this nonresponsiveness is mediated by suppressor T cells. The requirement of antigen association with cell membrane components and the general applicability of this method of inducing T cell nonresponsiveness are discussed.     

Involvement of dectin-2 in ultraviolet radiation-induced tolerance

Hapten sensitization through UV-exposed skin induces hapten-specific tolerance which can be adoptively transferred by injecting T cells into naive recipients. The exact phenotype of the regulatory T cells responsible for inhibiting the immune response and their mode of action remain largely unclear. Dectin-2 is a C-type lectin receptor expressed on APCs. It was postulated that dectin-2 interacts with its putative ligands on T cells and that the interaction may deliver costimulatory signals in naive T cells. Using a soluble fusion protein of dectin-2 (sDec2) which should inhibit this interaction, we studied the effect on contact hypersensitivity (CHS) and its modulation by UV radiation. Injection of sDec2 affected neither the induction nor the elicitation phase of CHS. In contrast, UV-induced inhibition of the CHS induction was prevented upon injection of sDec2. In addition, hapten-specific tolerance did not develop. Even more importantly, injection of sDec2 into tolerized mice rendered the recipients susceptible to the specific hapten, indicating that sDec2 can break established tolerance. FACS analysis of spleen and lymph node cells revealed a significantly increased portion of sDec2-binding T cells in UV-tolerized mice. Furthermore, transfer of UV-mediated suppression was lost upon depletion of the sDec2-positive T cells. Taken together, these data indicate that dectin-2 and its yet unidentified ligand may play a crucial role in the mediation of UV-induced immunosuppression. Moreover, sDec2-reactive T cells appear to represent the regulatory T cells responsible for mediating UV-induced tolerance.     

CD4 cell priming and tolerization are differentially programmed by APCs upon initial engagement

Bone marrow-derived APCs present both parenchymal-self and pathogen-derived Ags in a manner that elicits either T cell tolerization or immunity, respectively. To study the parameters that confer tolerogenic vs immunogenic APC function we used an adoptive transfer system in which naive TCR transgenic hemagglutinin (HA)-specific CD4(+) T cells are either tolerized upon encountering HA expressed constitutively as a parenchymal self-Ag (self-HA) or primed to express effector function upon encountering transiently expressed vaccinia-derived HA (viral-HA). When the duration of viral-HA presentation was extended for the period required to elicit tolerization toward self-HA, CD4 cell tolerization to viral-HA did not occur. Furthermore, CD4 cells exhibited both phenotypic as well as functional differences during early stages of tolerization and priming, suggesting that these divergent differentiation processes are programmed soon after the initial APC-CD4 cell interaction. When mice expressing self-HA were infected with an irrelevant vaccinia, CD4 cell tolerization still occurred, indicating that priming vs tolerization cannot be explained by pathogen-induced third parties (i.e., non-APCs) that act directly on CD4 cells. Taken together, these results suggest that CD4 cell tolerization to parenchymal self-Ags and priming to pathogen-derived Ags are initiated by functionally distinct APCs.     

Inhibition of T suppressor cell expression by histamine type 2 (H2) receptor antagonists

The effect of histamine type 2 (H2) receptor antagonists, cimetidine and ranitidine, on the induction and expression of hapten-specific suppressor T cells was studied. The activity of DNBSO3 -induced suppressor cells was evaluated after adoptive transfer to naive syngeneic recipients. Treatment with cimetidine or ranitidine markedly inhibited suppressor T cell activity in a dose-related manner and enhanced the contact sensitivity response to DNFB. Both H2 antagonists were effective in inhibiting the expression and, to a lesser extent, the induction of suppressor T cells. In contrast, norburimamide , a non-H2 antagonist structurally related to cimetidine, was inactive. The relevance of these findings to the clinical observation of cimetidine-induced reversal of acquired tolerance to dinitrochlorobenzene in anergic patients is discussed.     

Deletion of naive CD8 T cells requires persistent antigen and is not programmed by an initial signal from the tolerogenic APC

Activation of naive CD8 T cells in vivo requires the recognition of cognate peptide-MHC complexes on APCs. Depending upon the activation status of the APC, such recognition will promote either a vigorous immune response or T cell tolerance and deletion. Recent studies suggest that the initial signals provided by APCs are sufficient to program the proliferation of naive CD8 T cells and their differentiation into effector cells. In this study, we sought to determine whether an initial encounter with tolerogenic APCs was sufficient to program deletion of naive CD8 T cells. Surprisingly, we find that regardless of whether naive CD8 T cells were stimulated by activated or quiescent APCs, transfer of the activated T cells into an Ag-free host was sufficient to ensure survival. Thus, although the extent of clonal expansion and development of effector function is determined by the activation status of the stimulatory APC, peripheral clonal deletion requires persistent Ag and is not determined by the initial stimulatory event.     

Steady state dendritic cells present parenchymal self-antigen and contribute to, but are not essential for, tolerization of naive and Th1 effector CD4 cells

Bone marrow-derived APC are critical for both priming effector/memory T cell responses to pathogens and inducing peripheral tolerance in self-reactive T cells. In particular, dendritic cells (DC) can acquire peripheral self-Ags under steady state conditions and are thought to present them to cognate T cells in a default tolerogenic manner, whereas exposure to pathogen-associated inflammatory mediators during the acquisition of pathogen-derived Ags appears to reprogram DCs to prime effector and memory T cell function. Recent studies have confirmed the critical role of DCs in priming CD8 cell effector responses to certain pathogens, although the necessity of steady state DCs in programming T cell tolerance to peripheral self-Ags has not been directly tested. In the current study, the role of steady state DCs in programming self-reactive CD4 cell peripheral tolerance was assessed by combining the CD11c-diphtheria toxin receptor transgenic system, in which DC can be depleted via treatment with diphtheria toxin, with a TCR-transgenic adoptive transfer system in which either naive or Th1 effector CD4 cells are induced to undergo tolerization after exposure to cognate parenchymally derived self-Ag. Although steady state DCs present parenchymal self-Ag and contribute to the tolerization of cognate naive and Th1 effector CD4 cells, they are not essential, indicating the involvement of a non-DC tolerogenic APC population(s). Tolerogenic APCs, however, do not require the cooperation of CD4(+)CD25(+) regulatory T cells. Similarly, DC were required for maximal priming of naive CD4 cells to vaccinia viral-Ag, but priming could still occur in the absence of DC.     

Oral tolerance in experimental autoimmune encephalomyelitis. III. Evidence for clonal anergy.

We have recently reported that experimental autoimmune encephalomyelitis (EAE) can be suppressed by the oral administration of myelin basic protein (MBP). The oral introduction of 20 mg MBP together with a trypsin inhibitor results in inhibition of EAE clinical signs, decreased CNS histopathologic changes and dramatically reduced MBP-specific proliferative responses in fed and challenged Lewis rats. In the present study, we have investigated the mechanism underlying MBP-induced oral tolerance in EAE. Neither lymphoid cells (lymph node cells, spleen cells, Peyer's patch lymphocytes, thymocytes) nor humoral elements derived from tolerant donors were capable of transferring the tolerance to naive recipients. Moreover, lymphoid cells obtained from orally tolerant donors exhibited a marked decrease in their capacity to transfer EAE to naive recipient rats, even after in vitro activation with MBP or Con A. We observed that EAE could be readily transferred into orally tolerant rats using MBP-specific encephalitogenic T cell lines. In vitro cell mixing studies showed that the proliferation of lymphocytes from MBP-sensitized donors was not inhibited by the addition of lymphoid cells from tolerant donors, arguing against the role of a suppressor cell. Investigation of MBP-stimulated lymphokine production showed that both IL-2 and IFN-gamma levels were substantially decreased in spleen and lymph node cell cultures from MBP-fed rats compared to vehicle-fed control animals. Furthermore, limiting dilution analyses revealed that MBP-fed rats exhibited a profound decrease in MBP-reactive, IL-2-secreting lymphocytes relative to control animals. Thus, because lymphocytes from MBP-fed rats neither proliferate nor secrete IL-2 or IFN-gamma in response to MBP and we can find no compelling evidence for the role of suppressor cells, we propose that the oral administration of MBP results in a state of clonal anergy.     

Oral nickel tolerance: Fas ligand-expressing invariant NK T cells promote tolerance induction by eliciting apoptotic death of antigen-carrying, effete B cells

Whereas oral nickel administration to C57BL/6 mice (Ni(high) mice) renders the animals tolerant to immunization with NiCl2 combined with H2O2 as adjuvant, as determined by ear-swelling assay, it fails to tolerize Jalpha18-/- mice, which lack invariant NKT (iNKT) cells. Our previous work also showed that Ni(high) splenic B cells can adoptively transfer the nickel tolerance to untreated (Ni(low)) recipients, but not to Jalpha18-/- recipients. In this study, we report that oral nickel administration increased the nickel content of splenic Ni(high) B cells and up-regulated their Fas expression while down-regulating expression of bcl-2 and Bcl-xL, thus giving rise to an Ag-carrying, apoptosis-prone B cell phenotype. Although oral nickel up-regulated Fas expression on B cells of both wild-type Ni(high) and Jalpha18-/- Ni(high) mice, only the former showed a reduced number of total B cells in spleen when compared with untreated, syngeneic mice, indicating that iNKT cells are involved in B cell homeostasis by eliciting apoptosis of effete B cells. Upon transfer of Ni(high) B cells, an infectious spread of nickel tolerance ensues, provided the recipients are immunized with NiCl2/H2O2. As a consequence of immunization, Fas ligand-positive (FasL+) iNKT cells appeared in the spleen and apparently elicited apoptosis of Ni(high) B cells. The apoptotic Ni(high) B cells were taken up by splenic dendritic cells, which thereby became tolerogenic for nickel-reactive Ni(low) T cells. In conclusion, FasL+ iNKT cells may act as ready-to-kill sentinels of innate immunity, but at the same time assist in tolerance induction by eliciting Fas/FasL-mediated apoptosis of effete, Ag-containing B cells.     

A splenic requirement for the generation of suppressor T cells.

Tolerance to contact sensitization with DNFB may be induced by DNBSO3. This specific unresponsiveness may occur via one or both of two mechanisms--production of suppressor T cells or clone inhibition. We investigated the role of the spleen in this unresponsiveness. Splenectomized mice may be tolerized by i.v. injection of DNBSO3, but they are incapable of serving as donors of lymph node cells for transfer of tolerance to normal recipients. Kinetic studies indicated that the spleen must be present at least three days after tolerization in order to permit development of a significant number of suppressor cells in the peripheral lymph nodes. We interpret these results to indicate that 1) clone inhibition does not require the spleen, 2) the generation of suppressor T cells is dependent on the presence of the spleen, and 3) it is likely that tolerogens in this system induce suppressor cells in the spleen and some of these cells or their products leave the spleen to reach the peripheral lymph nodes.     

Autoreactive T cells revealed in the normal repertoire: escape from negative selection and peripheral tolerance

Self-reactive T cells are known to be eliminated by negative selection in the thymus or by the induction of tolerance in the periphery. However, developmental pathways that allow self-reactive T cells to inhabit the normal repertoire are not well-characterized. In this investigation, we made use of anti-small nuclear ribonucleoprotein particle (snRNP) Ig transgenic (Tg) mice (2-12 Tg) to demonstrate that autoreactive T cells can be detected and activated in both normal naive mice and autoimmune-prone MRL lpr/lpr mice. In contrast, autoreactive T cells of nonautoimmune Tg mice are tolerized by Tg B cells in the periphery. In adoptive transfer studies, autoreactive T cells from MRL lpr/lpr mice can stimulate autoantibody synthesis in nonautoimmune anti-snRNP Tg mice. Transferred CD4 T cells migrate to regions of the spleen proximal to the B cell follicles, suggesting that cognate B cell-T cell interactions are critical to the autoimmune response. Taken together, our studies suggest that anti-snRNP B cells are important APCs for T cell activation in autoimmune-prone mice. Additionally, we have demonstrated that anti-snRNP B cell anergy in nonautoimmune mice may be reversed by appropriate T cell help.     

Contrasuppressor cells that break oral tolerance are antigen-specific T cells distinct from T helper (L3T4+), T suppressor (Lyt-2+), and B cells

Continuous gastric intubation of mice with the T cell-dependent antigen sheep erythrocytes (SRBC) leads to a state of systemic unresponsiveness to parenteral SRBC challenge, a state termed oral tolerance. The systemic unresponsiveness of mice rendered orally tolerant to SRBC, however, is converted to humoral immune responsiveness by adoptive transfer of effector T contrasuppressor (Tcs) cells. In this study, the authors have isolated and characterized the Tcs cell subset, from the spleens of orally immunized mice, which abrogates oral tolerance. This Tcs cell is a novel cell type, which can be separated from functional T suppressor (Lyt-2+) and T helper (L3T4+) cells, and the effector Tcs cell exhibits a Lyt-1+, 2-, L3T4- phenotype. Furthermore, contrasuppression is not mediated by B cells, including those of the Lyt-1+ phenotype. Adoptive transfer of splenic Lyt-1+, 2-, L3T4- T cells from C3H/HeJ mice given oral SRBC for 21 to 28 days and splenic Lyt-1+, 2-, L3T4- T cells of C3H/HeN mice orally immunized for a shorter interval abrogated oral tolerance. Furthermore, separation of Lyt-1+ T cells into L3T4+ and L3T4- subsets by flow cytometry resulted in Lyt-1+, L3T4+ T cells with helper but not contrasuppressor function, whereas the Lyt-1+, L3T4- T cell fraction abrogated oral tolerance even though it was without helper activity. This Tcs cell subset was also effective when added to cultures of tolerized spleen cells derived from SRBC-fed mice. The effector Tcs cells are antigen-specific, because Tcs cells from SRBC-immunized mice reverse tolerance to SRBC but not to horse erythrocytes (HRBC), and Tcs cells from HRBC-immunized mice reverse tolerance to HRBC but not to SRBC. When splenic T3 (CD3)-positive T cells (Lyt-1+, 2-, and L3T4-) were separated into Vicia villosa-adherent and nonadherent subpopulations, active contrasuppression was associated with the T3-positive and Vicia villosa-adherent T cell fraction. Thus, a distinct Lyt-1+, 2-, L3T4- T cell subset that contains a T3-T cell receptor complex, which can regulate oral tolerance, is present in spleens of orally immunized mice.     

Dendritic cells genetically engineered to express IL-10 induce long-lasting antigen-specific tolerance in experimental asthma

Dendritic cells (DCs) are professional APCs that have a unique capacity to initiate primary immune responses, including tolerogenic responses. We have genetically engineered bone marrow-derived DCs to express the immunosuppressive cytokine IL-10 and tested the ability of these cells to control experimental asthma. A single intratracheal injection of OVA-pulsed IL-10-transduced DCs (OVA-IL-10-DCs) to naive mice before OVA sensitization and challenge prevented all of the cardinal features of airway allergy, namely, eosinophilic airway inflammation, airway hyperreactivity, and production of mucus, Ag-specific Igs, and IL-4. OVA-IL-10-DCs also reversed established experimental asthma and had long-lasting and Ag-specific effects. We furthermore showed, by using IL-10-deficient mice, that host IL-10 is required for mediating the immunomodulatory effects of OVA-IL-10-DCs and demonstrated a significant increase in the percentage of OVA-specific CD4(+)CD25(+)Foxp3(+)IL-10(+) regulatory T cells in the mediastinal lymph nodes of OVA-IL-10-DC-injected mice. Finally, adoptive transfer of CD4(+) mediastinal lymph node T cells from mice injected with OVA-IL-10-DCs protected OVA-sensitized recipients from airway eosinophilia upon OVA provocation. Our study describes a promising strategy to induce long-lasting Ag-specific tolerance in airway allergy.     

Transfer of regulatory properties from tolerogenic to proinflammatory dendritic cells via induced autoreactive regulatory T cells

Infectious tolerance is a term generally assigned to the process through which regulatory T cells (Tregs) transfer immunoregulatory properties to other T cells. In this study, we demonstrated that a similar process applies to human dendritic cells (DCs), albeit through a different mechanism. We induced and cloned proinsulin-specific Tregs using tolerogenic DCs and investigated mechanisms by which induced Ag-specific regulatory T cells (iaTregs) endorse the suppressive effects. iaTregs expressed FOXP3, programmed death-1, and membrane-bound TGF-β and upregulated IL-10 and CTLA-4 after stimulation with the cognate Ag. The iaTregs suppressed effector T cells only when both encountered the cognate Ags on the same APCs (linked suppression). This occurred independently of IL-10, TGF-β, programmed death-1, or CTLA-4. Instead, iaTregs used a granzyme B-mediated mechanism to kill B cells and monocytes, whereas proinflammatory DCs that resisted being killed were induced to upregulate the inhibitory receptors B7 (family) homolog 3 and ICOS ligand. These re-educated mature monocyte-derived dendritic cells (mDCs) suppressed effector T cells and induced IL-10-producing cells from the naive T cell pool. Our data indicated that human tolerogenic DCs confer infectious tolerance by inducing Ag-specific Tregs, which, in turn, re-educate proinflammatory mature DCs into DCs with regulatory properties.     

Peptic fragments of bovine serum albumin bind antigen-specific T suppressor cells from orally tolerized mice

The antigenic structures capable of binding immunoregulatory T cells have been investigated. The functional properties (suppression or help) of BSA-specific T cells from primed or orally tolerized mice with capacity to adhere to bovine serum albumin or its peptic fragments were examined in reconstitution experiments in which splenic T-cell populations together with naive B cells were transferred into irradiated syngeneic recipients. Antigen-specific T suppressor cells isolated from mice tolerized to BSA adhered to peptic fragments of BSA as well as to the intact antigen. BSA-specific T helper cells adhered only to the intact antigen. Our data suggest that the preferential activation of T suppressor cells following administration of peptic fragments may be due to their ability to adhere to such fragments. These findings offer a novel approach of separation and identification of T suppressor cells and may be useful in further studies of immunosuppression.     

Antigen-specific T contrasuppressor factor in cell-mediated immunity: interactions leading to eradication of the tolerant state

Interactions between a T cell-derived, antigen-specific, contrasuppressor factor (TcsF) and immune T cells that block the action of T suppressor factors and allow the transfer of cellular immunity into tolerant recipients are described. Immune T cells from contact-sensitized donors are capable of transferring specific immunity into normal recipients but not into animals rendered tolerant to the specific antigen. Brief exposure of the immune cells to the TcsF enables the effective transfer of immunity into such tolerant recipients. In addition, treated immune cells become resistant to subsequent exposure to T suppressor factor (capable of inhibiting transfer of immunity to normal recipients). A cyclophosphamide-sensitive, I-J+, Ly-2 T transducer cell is required in the immune donor cell population for contrasuppression to be induced by the TcsF plus specific antigen. These cells release an antigen-non-specific contrasuppressive factor capable of rendering immune targets, depleted of transducer cells, resistant to suppression (either by suppressor factor or in the tolerant recipient). The results indicate that contrasuppression in contact sensitivity is antigen specific and that the balance of suppression and contrasuppression determines tolerance vs responsiveness in this system. The symmetrical resemblance of the contrasuppressive interactions to those of suppression in contact sensitivity are discussed.