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.     

Dextran augments delayed-type hypersensitivity by interrupting one limb of the suppressor cascade

We have studied the immunomodulatory effect of dextran on the development of delayed-type contact hypersensitivity to a hapten in mice. Administration of an optimal dose of dextran 2 hours before applying picryl chloride to abdominal skin caused a twofold rise in the level of hapten-specific DTH. A study of the kinetics of development of DTH under the influence of dextran showed that comparable levels of response could be seen 2 days earlier in treated than in untreated mice, i.e., on the third day in contrast to the fifth day after sensitization. The peak of the responses, while greater in dextran-treated mice than in normal controls, remained the same at 5 days. Adoptive transfer studies revealed that comparable levels of DTH were conferred upon recipient mice by half the number of splenic cells from dextran-treated mice than that required from normal sensitized mice. Because several suppressor mechanisms are known to down-regulate DTH, we have studied dextran's effect on the neutralization of these systems as a possible explanation for its enhancing capabilities. Detailed examination was made of dextran's effect on the two suppressor T cells, Ts1 and Ts3, that act in tandem as well as its effect on the Ts1 and macrophage that work in combination. Both systems depress the efferent limb of DTH. We have found that dextran blocks the Ts1-macrophage pathway that controls DTH. Ts1 was found to arise normally in mice pretreated with dextran. Furthermore, Ts1 from dextran-treated mice produced TsF1 normally. However, we have found that dextran interferes with the production of macrophage suppressor factor (M phi-SF). Interference was partial when dextran was introduced during the interval in which macrophages were being armed with TsF1, and it was complete when dextran was put with pre-armed macrophages before they were triggered with antigen for production of M phi-SF. On the other hand, the Ts1-Ts3 limb of suppression remained unaffected by exposure to the immunomodulator. We found Ts3 arose normally in hapten-sensitized mice that had been pretreated with dextran. In addition, Ts3 became armed with TsF1 in vitro in the presence of dextran since the cells functioned properly to suppress mature DTH effector cells. Finally, TsF3 was able to act in vitro upon DTH effector cells despite the presence of dextran.(ABSTRACT TRUNCATED AT 400 WORDS)     

The role of macrophages in B cell tolerance. I. Antigen-specific failure of Thy-1, Ly-2 negative adherent cells from tolerant mice to reconstitute immunocompetence in adherent cell deficient spleen cells

T-Cell-independent B-cell tolerance to the hapten derivatives of carboxymethyl cellulose (CMC) or methyl cellulose (MC) appears to be controlled by Thy-1-, Ly-2- adherent (A) cells contained in the spleen or peritoneal fluid. Immunocompetence in nonadherent (NA) normal spleen cells could be restored in vitro by irradiated A cells from normal mice. However, NA cells reconstituted with irradiated A cells derived from hapten specifically tolerant mice failed to respond to the same hapten, but responded normally to an immunogenic challenge with another unrelated antigen. A cells that had been preincubated at 4 degrees C with hapten derivatized MC also failed to restore immunocompetence. While preincubation of unfractionated spleen cells with the tolerogen under the same conditions resulted in B-cell unresponsiveness, such treatment of NA cells failed to render B cells tolerant. Treatment of A cells from tolerant mice with the reducing agent potassium iodide (KI) in vitro restored their capacity to render cultures of NA cells immunocompetent to the relevant hapten. Moreover, treatment with KI of spleen cells from mice injected with the tolerogen was shown to render them responsive. We suggest that B-cell tolerance induced by hapten derivatives of CMC and MC is mediated by suppressive macrophages contained among A cells. Certain subpopulations of macrophages are known to exert cytotoxic effects upon target cells by the release at close range of oxidating agents. We postulate that hapten derivatized CMC and MC, through unique properties of the carrier, bind to and possibly activate macrophages rendering them specifically suppressive for hapten binding B cells.     

The induction of hapten-specific immunological tolerance and immunity in B lymphocytes. V. Evidence for b-cell deletion in vitro with serum from tolerant mice.

The serum from mice that had been rendered specifically tolerant (TolS) to the trinitrophenyl (TNP) hapten by the injection of trinitrobenzenesulfonic acid (TNBS) is effective in the in vitro induction of immunological unresponsiveness in murine spleen cells. This tolerance system was investigated with particular emphasis upon the mode of induction. The observed inhibition by TolS of responses to the thymic-independent (TI) antigen TNP-lipopolysaccharide (TNP-LPS) was stable following adoptive transfer to lethally irradiated recipients and was due neither to the delay of in vitro responsiveness nor to effector cell blockade at the level of the antibody-forming cell. Neither suppressor cells nor cell-bound tolerogen carry-over were responsible for the tolerance induced by TolS. TNP-LPS doses, including a wide range of polyclonal activating concentrations, were ineffective in reversing the unresponsive state induced by cocultivation with TolS. Additionally, unconjugated LPS in either fetal calf serum (FCS)-containing or FCS-free cultures did not break tolerance. This failure of polyclonal activating substances to reverse the unresponsive state suggests that blockade of TNP-specific receptors is not the mechanism of tolerogenesis, since such compounds trigger cells polyclonally through nonimmunoglobulin receptors. Tolerance induced by incubation of spleen cells with TolS for 24 hr followed by extensive washing was stable whether the immunogenic stimulus was the TI antigen TNP-LPS or the thymic-dependent (TD) form of the hapten, TNP-sheep erythrocytes (TNP-SRC). Washing spleen cells at elevated temperatures after preculturing with TolS to avoid possible reassociation of surface Ig (sIg)-bound TNP conjugates did not lead to escape from tolerance. Antigen-free incubation for 24 hr following cultivation with TolS was equally unsuccessful in reversing the unresponsive state. Thus, extensive washing following tolerance induction and antigen-free cultivation where unblocking or turnover and resynthesis of sIg receptors should have taken place provided no support for receptor blockade as the mode of in vitro induction and maintenance of tolerance by TolS. Treatment with the proteolytic enzyme pronase with the intention of removing potential tolerogen from the cell surface revealed a stable tolerant state. Incubation with anti-Ig or anti-TNP antisera under conditions designed to allow capping and removal of sIg-bound tolerogen or surface-bound TNP conjugates also failed to reverse the tolerance induced by incubation with TolS. The results presented here and previously lend no support to active or passive suppression or blockade of reactive cells as the mechanism of tolerance induction in vitro by TolS. The data are consistent with the hypothesis that TolS-induced unresponsiveness is due to a functional deletion of TNP-specific B lymphocytes. Furthermore, the similarities observed between the induction of tolerance by TNBS injection and TolS-induced unresponsiveness are consistent with the suggestion that TNBS-induced tolerance in vivo is mediated by a component of TolS which is active as a tolerogen in vitro.     

The induction of tolerance to DNFB contact sensitivity by using hapten-modified lymphoid cells. III. Effects of hapten concentration on the ability of MLS-disparate cells to induce rapid unresponsiveness

We investigated genetic restrictions in the induction of immediate tolerance to DNFB contact sensitivity in mice. Using spleen cells from various donor strains haptenated at 500 micro M DNFB, we were unable to detect any restrictions in tolerance induction in recipients that were either syngeneic or allogeneic to the donor strain. However, if the concentration of hapten used in the in vitro labeling was decreased (from 500 micro M to 2.5 to 5 micro M DNFB), differences in tolerogenesis between the various donor strain haplotypes were found. Haptenated spleen cells labeled with 5 micro M DNFB produced a profound level of unresponsiveness in allogeneic recipients but produced minimal tolerance in syngeneic animals. This tolerant state was shown to be antigen-specific and was not produced by unmodified allogeneic cells alone. Further genetic analysis demonstrated that an efficient tolerant state was produced when the donor of the tolerogen and recipient differed at the MLS locus rather than at either the MHC or minor regions. This phenomenon required viable, Thy 1-bearing cells in the haptenated donor population for efficient tolerogenesis to DNFB contact sensitivity.     

Immunologic tolerance to dinitrophenylated human gamma globulin induced via colostrum

Immunologic unresponsiveness or tolerance was induced in neonatal mice via colostrum by injection of dinitrophenylated human gamma globulin (DNP-HGG) into the mother on the day of birth. Unresponsiveness persisted in the neonates for at least 21 weeks. This longlasting tolerance appeared to be the result of an unresponsiveness to the carrier determinants. Hapten-specific B-cell tolerance was assessed in mice receiving high- or low-epitope-density tolerogen and it was observed that the low-epitope-density tolerogen (DNP₁HGG) resulted in carrier-specific tolerance only. Although mice tolerized with the high-epitope-density conjugates were found to be slightly hyporesponsive in their in vivo B-cell responses, their in vitro hapten-specific responses were normal. This tolerant state induced via colostrum was compared to tolerance induced in utero. This earlier contact with tolerogen resulted in more profound alterations in hapten-specific B-cell responses. An additional interesting finding was that the colostrally induced tolerant state was transmitted to the next generation.     

Membrane defects of the tolerant B cell. I. Failure of antigen-induced capping.

In order to study the membrane function of tolerant B antigen-binding cells, tolerance to the trinitrophenyl (TNP) determinant was induced in mice by injecting the reactive form of the hapten, trinitrobenzene sulfonic acid (TNBS). By appropriate transfer experiments, Fidler and Golub (J. Immunol.112, 1891, 1974) had previously shown that this form of tolerance is a B-cell property, induced and expressed in the absence of T cells. Hapten inhibition demonstrated the TNP-specificity of receptors on TNP-donkey erythrocyte(TNP-D)-binding cells in tolerant and nontolerant mice. About 88% of these cells were B cells by immunofluorescence, and the remainder were T cells. In the tolerant mice, challenge with TNP-sheep erythrocytes failed to expand the TNP-binding population, but sheep erythrocyte binders and anti-sheep plaque-forming cells expanded normally. Despite little or no change in TNP-binding cell numbers after tolerance induction, the TNP-binding cells of tolerant animals could not cap their receptors, in contrast to the sheep erythrocyte-binding cells from the same animals which capped normally. Although there is no anti-TNP plaque-forming cell response when tolerogen and immunogen are given simultaneously, capping failure is not evident until 2–4 days after tolerogen exposure. By Day 7, substantial recovery of immune responsiveness had occurred, yet even 12 months after a single dose of tolerogen there was no restoration of capping. Thus despite the association of both capping failure and unresponsiveness with tolerogen exposure, these lymphocyte functional defects appeared not to be causally related.     

Interference with tolerance induction in vivo by inhibitors of prostaglandin synthesis

Prostaglandins (PG) have been implicated as modulators of both humoral and cellular immune responses. In order to evaluate a possible role for PG in tolerance, the effect of inhibitors of prostaglandin synthesis on tolerance induction and circumvention has been investigated. Injection of deaggregated human gamma-globulin (DHGG) into A/J mice leads to unresponsiveness to a subsequent challenge with immunogenic aggregated human gamma-globulin (AHGG). Administration of indomethacin (IM) or acetylsalicylic acid (ASA) shortly before and after DHGG injection prevents tolerance induction. PGE2 reverses the tolerance overriding effect provided by IM. IM is not able to overcome unresponsiveness when given 10 and 20 days after tolerance induction, at a time point when both T and B lymphocytes are tolerant. As previously shown, lipopolysaccharide (LPS) both inhibits the induction of tolerance to HGG and circumvents tolerant T helper cells late in tolerance when competent B cells are present. In contrast, IM is unable to circumvent T-helper cell tolerance when given at Day 60 after tolerogen, when B cells (but not T cells) are responsive. Furthermore, LPS acts as an adjuvant, B-cell mitogens, inducer of polyclonal Ig secretion, and primes mice when given with tolerogen, while IM has none of these properties. These results indicate a difference between the effects of IM and LPS on tolerance and a possible role of PG in DHGG-mediated tolerance induction.     

Interaction of gangliosides with B cells in splenic fragment cultures

The effect of gangliosides upon murine adult B cells at the single precursor cell level was examined using the splenic focus assay. Adult B cells were stimulated in in vitro organ fragment culture by a hapten-modified carrier protein in the presence of an excess of carrier-primed T cells. The addition of a potential tolerogen in the form of antigen coupled to a carrier not previously presented to the T cells resulted in a temporary unresponsiveness of the onset of antibody production in adult B cells, but not a permanent state of tolerance. This delay could be eliminated by the addition of purified murine gangliosides during the presentation of the hapten coupled to the unrecognized carrier. The ganglioside preparation was fractionated by ion-exchange chromatography and the active fraction was found to be a disialoganglioside. These results suggest that the ganglioside may interfere with membrane receptor-related events occurring during or after antigen binding or cross-linking to responding B cells.     

Tolerance susceptibility of newly generating memory B cells

Newly generating memory B cells rapidly accumulate somatic mutations that can alter their Ag-combining sites and potentially engender recognition of self determinants. To investigate the possibility that, during their emergence secondary B cells pass through a window of tolerance susceptibility, we have examined the in vitro generation of memory B cells in the presence or absence of tolerogen. The findings indicate that, before antigenic stimulation, precursors to memory B cells are resistant to tolerance induction. However, 2 to 7 days after T cell-dependent antigenic stimulation, newly emerging hapten-specific secondary B cells can be inactivated by the presence of hapten on a carrier not recognized by available Th cells. This inactivation can be blocked by the presence of free hapten and can be competed by the presence of immunogen. Inactivation of newly generating secondary B cells appears less specific than the tolerance induction of immature neonatal or bone marrow B cells because inactivation can be accomplished by cross-reactive determinants. Interestingly, the presence of tolerogen after primary stimulation did not preclude the generation of cells responsive to a third in vitro stimulation. Therefore, whereas newly emerging memory B cells are highly susceptible to inactivation, the progression of the clones of progenitors to memory B cells appears resistant to tolerance induction.     

Comparison of the ease of tolerance induction in thymus and bone marrow of three strains of mice

Three strains of mice which vary in their susceptibility to induction of immune tolerance with human gamma-globulin were studied to evaluate the cellular basis for their sensitivity to induction of the unresponsive state. Tolerance induction in BALB/c mice was difficult to establish, while tolerance induction was easily achieved in C57BL/6 and CBF₁ (BALB/c × C57BL/6) mice. The degree of unresponsiveness obtained with various tolerogen doses in intact C57BL/6 and CBF₁ mice was reflected in the sensitivity of their thymocytes to the production of the unresponsive state. In the BALB/c mouse strain slight immune suppression observed at low tolerogen doses was correlated with bone marrow cell unresponsiveness while significant levels of tolerance observed at a high tolerogen dose was due to suppression of thymus cells. It was apparent that CBF₁ mice had inherited both thymus cells and bone marrow cells which exhibited the sensitivity to induction of immune tolerance characteristic of those same cells of their C57BL/6 parent.     

Uptake of apoptotic antigen-coupled cells by lymphoid dendritic cells and cross-priming of CD8(+) T cells produce active immune unresponsiveness

The induction of immunologic unresponsiveness by i.v. administration of Ag-coupled lymphoid cells has been studied extensively, but the mechanisms remain unclear. We have further explored this model by examining the role of Fas/Fas ligand (FasL)-mediated apoptosis. Using i.v. injection of trinitrophenyl-coupled splenocytes (TNP-spl) as tolerogen, we found that Fas signaling for apoptosis in the spleen cells delivered by FasL in the recipient is the critical event. The requirement for Fas and FasL was overcome by prior induction of apoptosis in TNP-spl, making the tolerogen 100 times more potent. Prevention of apoptosis by a caspase inhibitor blocks tolerance. Interestingly, while blocking CD40/CD40 ligand interaction does not prevent tolerance induction, an agonist anti-CD40 Ab turns tolerogenic TNP-spl into an immunizing Ag. Studies further showed that tolerance is induced through cross-presentation of Ag in a class I MHC-dependent manner by CD8(+)CD11c(+) lymphoid-derived dendritic cells to regulatory T cells. The results provide a mechanism for a well-established method of inducing immunologic unresponsiveness.     

Mechanisms of B cell tolerance. I. Tolerance to dextran B1355 induced with the oxidized dextran.

The bacterial dextran B1355, which is normally a potent thymus-independent immunogen, was made tolerogenic by oxidation. The injection of the oxidized dextran into BALB/c mice before, at the same time, or up to 4 days after the injection of the immunogenic form of the dextran resulted in a marked immunologically specific suppression of the number of anti-dextran antibody-forming cells found in the spleen. This suppression resulted from a direct inactivation of antibody-forming cell precursors rather than from either inhibition of antibody secretion or the exhaustive utilization of precursor B cells that have been observed in other tolerance systems. A substantial degree of tolerance was achieved after only a 1-hr in vivo exposure of the spleen cells to the tolerogen. At a dose of 1 mg of oxidized dextran per mouse, tolerance persised for at least 3 weeks. A complete recovery was apparent by 10 weeks. The stability of the tolerance was demonstrated by transferring tolerant spleen cells to irradiated recipients. The response in the recipient animals to an immunogenic dextran challenge remained suppressed. It appears that the tolerogenicity of the oxidized dextran is due to its ability to couple covalently with free amino groups in or near the receptor site of the cell membrane via the reactive dialdehyde groups of the dextran.     

Antigen-induced in vitro inhibition of immune responsiveness

Addition of the dinitrophenyl derivative of the copolymer of d-glutamic acid and d-lysine (DNP-d-GL) or dinitrophenyl bovine γ-globulin (DNP-BGG) to spleen cell cultures specifically inhibited their capacity to produce an anti-DNP plaque-forming cell (PFC) response to the T-independent antigen dinitrophenylated polyacrylamide beads (DNP-PAA) or to the T-dependent antigen TNP-burro erythrocytes. The degree of unresponsiveness was dependent upon the tolerogen concentration and the duration over which the tolerogen was present in the culture. Treatment with rabbit anti-mouse brain antiserum and complement did not alter the induction of unresponsiveness suggesting a state of B-cell tolerance. Culture of spleen cells for 4 days in the absence of antigen led to the appearance of nonspecific suppressor activity which was demonstrable by its effect on the response of fresh spleen cells to antigen. Preculture in the presence of the immunogen DNP-PAA induced both nonspecific and specific suppressor activities. Induction of specific suppressor activity was not prevented by the presence of the tolerogen DNP-D-GL in the culture. The suppressor activity resided in an adherent T-cell population and did not appear to require macrophages for its induction.     

Cellular events in tolerance. V. Detection, isolation and fate of lymphoid cells which bind fluoresccinated antigen in vivo.

The binding of tolerogen to specific receptors of lymphocytes and the subsequent fate of such cells was directly studied in Lewis rats injected with fluorescein-labeled sheep gamma globulin (F-SGG). This tolerogen produced unresponsiveness both in SGG-specific T cells (carrier tolerance) and F-specific antibody-forming cell precursors. The former (T-cell tolerance) was still significant more than 60 days after tolerogen whereas tolerance in the latter (B-cell tolerance) had waned by that time.Cells which have bound the tolerogen (antigen-binding cells, ABC) in vivo were detectable by direct immunofluorescence of washed spleen cell suspensions from rats injected with F-SGG up to 7 days previously. These cells were isolated using antifluorescein affinity columns, and shown to contain immunocompetent precursors for F- and SGG specific responses.The frequency of such ABC was between 30 and 80 per 10⁵ spleen, lymph node or bone marrow cells; no ABC were detected in the thymus. Both Ig positive and Ig negative cells were found to be ABC; Ig negative ABC usually showed a “capped” fluorescent pattern whereas Ig positive ABC generally were “spotted.”By 10 days after injection, ABC were not detectable in the spleen, lymph nodes, thymus or bone marrow of tolerant rats. Furthermore, reinjection of F-SGG after this time did not label any cells. This suggests that antigen-binding cells are not present at this time or that such cells, if available, lack receptors. In contrast, rats previously injected with a lower non-tolerogenic dose of F-SGG or an immunogenic form (F-SGG on bentonite) possessed cells at these later times which could be labeled with F-SGG. Thus, ABC remain detectable following immunogen or a subtolerogeic dose of F-SGG, but disappear in tolerant rats.By approximately 40 days after initial high dose tolerogen injection (when B cell tolerance has started to wane), cells capable of binding a second dose of F-SGG again became detectable. It is suggested that high doses of F-SGG are bound by specific lymphocytes (identifiable as ABC) and that these cells either fail to regenerate new receptors or die. As tolerance begins to wane, either new receptors or new cells are generated.     

Cellular events in tolerance IX: Maintenance of immunological tolerance in the presence of normal B-cell precursors and in the absence of demonstrable suppression

The cellular events involved in immunological tolerance to fluoresceinated sheep gammaglobulin (FL-SGG) were analyzed at the level of hapten-specific B cells. One single iv injection of FL-SGG induced tolerance as measured by challenge with thymus-dependent (FL-KLH) or thymus-independent (FL-Ficoll) antigens in vivo or thymus-independent (FL-LPS) antigen in vitro. As noted earlier, unresponsiveness was maintained until 6–8 weeks after tolerance induction. Limiting-dilution precursor analysis demonstrated a reduction in B-cell precursors on Day 7 after tolerogen treatment; precursor frequencies returned to control levels by 3–4 weeks. This recovery of precursors in the presence of stable tolerance was not due to suppressor activity. Rather, results show that tolerant hapten-specific B cells are clonally anergic and display a reduced burst size in response to antigen. Hence, unresponsiveness is maintained in the presence of apparently normal precursor levels by an intrinsic defect in antigen-specific B cells.     

IL-12 breaks dinitrothiocyanobenzene (DNTB)-mediated tolerance and converts the tolerogen DNTB into an immunogen

Epicutaneous application of dinitrothiocyanobenzene (DNTB) induces tolerance against its related compound dinitrofluorobenzene (DNFB), because DNTB-pretreated mice cannot be sensitized against the potent hapten DNFB. This tolerance is hapten-specific and transferable. In this study, we demonstrate that IL-12 can break DNTB-mediated tolerance. Furthermore, naive mice treated with IL-12 before DNTB application responded to DNFB challenge with a pronounced ear swelling response without previous sensitization to DNFB, showing that IL-12 can convert the tolerogen DNTB into an immunogen. No differences in numbers or regulatory activity were observed between CD4+CD25+ regulatory T cells isolated from mice treated with DNFB, DNTB, or IL-12 followed by DNTB. However, the number of CD207+ Langerhans cells in regional lymph nodes of DNTB-treated mice was significantly lower than in animals treated with DNFB or IL-12 plus DNTB. Additionally, CD11c+ dendritic cells (DC) isolated from regional lymph nodes of DNTB-treated mice had a significantly lower ability to stimulate T cell proliferation and produced reduced amounts of inflammatory cytokines. Application of both DNFB and DNTB induced apoptotic cell death of DC in the epidermis and the regional lymph nodes. However, the number of apoptotic DC in regional lymph nodes was significantly higher in DNTB-treated animals compared with mice treated with DNFB or IL-12 plus DNTB. Therefore, we conclude that DNTB-mediated tolerance is secondary to inefficient Ag presentation as a result of apoptotic cell death of DC and that IL-12 converts the tolerogen DNTB into an immunogen by preventing DNTB-induced apoptosis of DC.     

Concomitant administration of hapten and IL-2-toxin (DAB486-IL-2) results in specific deletion of antigen-activated T cell clones

During the proliferative burst after Ag recognition, T cells express cell-surface, high-affinity IL-2R. The importance of IL-2R+ T cells in supporting/mediating tissue injury has been documented by the ability of mAb anti-IL2R therapies to prevent allograft rejection and autoimmunity. The delayed-type hypersensitivity (DTH) response, an experimental model of T-dependent immunity, offers the possibility of studying responses mounted against defined Ag. We previously reported that the chimeric IL-2 toxin (DAB486-IL-2) prevents DTH responses and selectively eliminates activated IL-2R bearing CD4 and CD8 T cells from lymph nodes draining the site of inflammation. We have examined the duration of immunosuppression and relative specificity of action of DAB486-IL-2 and anti-CD3 mAb for Ag-activated clones in a murine model of DTH using two different noncross-reacting haptens. Treatment with DAB486-IL-2 generates a state of selective unresponsiveness to subsequent challenge with the hapten introduced during the therapeutic period. Immediately after cessation of DAB486-IL-2 therapy, immunization with an unrelated hapten induces a normal vigorous immune response. By comparison, anti-CD3 mAb treatment causes a broad immunosuppression because unrelated haptens introduced after anti-CD3 therapy do not evoke a vigorous immune response. After cessation of DAB486-IL-2 toxin treatment response to the hapten is eventually restored probably by cells trafficking from the thymus, because thymectomized hosts remain unresponsive to the hapten. Taken together these data reinforce the role of the IL-2R as an important target for immunosuppression in T cell-mediated immune reactions. DAB-486-IL-2 treatment confers highly selective immunosuppression.     

Effect of priming with a thymus-independent antigen on susceptibility to B-cell tolerance.

The effects of priming on the susceptibility of B-cell subsets to tolerance induction have been tested in a model system in which anti-immunoglobulin (anti-Ig) has been employed as a surrogate for tolerogen. T-cell-depleted B cells were primed in vitro with fluorescein or trinitrophenylated Ficoll (a thymus-independent (TI) antigen) and then exposed overnight to anti-Ig to attempt to induce B-cell anergy. Primed cells were relatively resistant to this tolerance protocol and resistance was hapten specific. The dose response and kinetics suggested that this process was not due to receptor blockade or modulation, but was an active process. Moreover, this priming for resistance to tolerance was reproduced in vivo upon intraperitoneal treatment with haptenated Ficoll. Such in vivo priming for tolerance resistance was long-lasting and did not occur with a thymus-dependent priming protocol with fluoresceinated hemocyanin. These results are discussed in terms of TI priming to drive B cells into cycle and express novel functional and phenotypic properties.     

The induction of cell-mediated immunity and tolerance to insulin with insulin coupled to syngeneic lymphoid cells

The induction of delayed type hypersensitivity (DTH) and tolerance to DTH against bovine insulin in mice were explored. DTH was induced with insulin in complete Freund's adjuvant (CFA) and was assessed by ear swelling in vivo and by antigen-driven cell proliferation in vitro. Using the concept that thymus cell unresponsiveness is most easily accomplished via antigen on syngeneic membranes, tolerance was induced by iv injection of syngeneic lymphoid cells which had been coupled to insulin with carbodiimide. Mice tolerized with insulin-coupled cells and then sensitized with insulin-CFA had diminished ear swelling in vivo and decreased insulin-driven cell proliferation in vitro. This unresponsiveness was antigen specific but was also inconstant in degree with regard to suppression of ear swelling, most likely because of variability in coupling of insulin to cells. Proliferative responses were more uniformly suppressed, suggesting the possibility that two target cells were being tolerized. Thus, as with other proteins, the biologically active insulin can be used to induce tolerance.