Neonatal Tolerance Induction Research Articles

Neonatal tolerance induction by class II alloantigens activates IL-4-secreting, tolerogen-responsive T cells.

Neonatally induced tolerance of class II MHC alloantigens in mice of the A/J strain background is achieved without evident clonal deletion, because lymphoid cells from tolerant animals proliferate in mixed lymphocyte reactions against tolerogen-bearing stimulators. However, the pattern of lymphokines produced in bulk cultures by these tolerogen-reactive cells is unusual in that, unlike lymphocytes from nontolerant normal mice, lymphocytes from tolerant mice produce measurable amounts of IL-4 when stimulated with tolerogen. Using limit dilution analysis, we have determined that the ability to detect IL-4 in bulk cultures is caused by a high frequency of precursors of Ag-specific IL-4 secreting (pIL-4) cells among tolerant, but not normal, responder lymphocytes. Moreover, after repeated in vitro exposure to class II alloantigens, and after in vivo grafting with class II-disparate skin, the frequency of pIL-4 cells rises among lymphocytes from normal mice, eventually reaching levels similar to those found in class II tolerant mice. Because in normal mice a high frequency of class II-reactive pIL-4 cells reflects the "primed" state, we conclude that a subset of T cells that resemble Th2 cells is similarly primed in neonatally tolerized mice. We propose that this priming is achieved by the neonatal inoculation of semiallogeneic bone marrow cells. Because no expansion in the clone size of tolerogen-specific precursors of Ag-specific IL-2-secreting T cells (pIL-2) is observed among tolerant animals, and because the pIL-2 cells from tolerant mice are incapable of differentiating into cytotoxic and delayed hypersensitivity effector cells, we further propose that the precociously primed pIL-4 cells function as "suppressor" cells, helping to maintain the tolerant state.

Autoimmune syndrome after induction of neonatal tolerance to alloantigens. CD4+ T cells from the tolerant host activate autoreactive F1 B cells.

The induction of transplantation tolerance to H-2b alloantigens in BALB/c (H-2d) mice by neonatal injection of (C57BL/6 x BALB/c)F1 spleen cells, produces an autoimmune lupus-like syndrome due to an activation of persisting F1 donor B cells. This syndrome is characterized by hypergammaglobulinaemia, high levels of anti-DNA antibodies, as well as by circulating immune complexes and glomerular deposits of Ig. The role of host T cells in this model was investigated by using athymic BALB/c nu/nu mice as recipients of normal (C57BL/6 x BALB.Igb)F1 spleen cells. In these "tolerized" BALB/c nu/nu mice, there was a persistence of F1 donor B cells but none of the autoimmune features were expressed, conversely to tolerized BALB/c nu/+ littermates. The injection of CD4+CD8- T lymphocytes from adult normal BALB/c mice in 3-wk-old tolerized BALB/c nu/nu mice triggered the appearance of all the autoimmune findings observed in euthymic tolerant mice. The autoantibodies were produced by persisting F1 donor B cells as shown by allotype analysis. More strikingly, a similar triggering of the autoimmune syndrome, including high titers of anti-DNA IgG antibodies and circulating immune complexes, was observed after injection of CD4+CD8- T cells from 2-wk-old tolerant BALB/c mice into "tolerized" BALB/c nu/nu mice. The anti-ssDNA antibodies were shown to bear only the Ighb allotype, indicating their exclusive origin from F1 donor B cells. These results imply that CD4+ T cells from the tolerant mice are necessary for the activation of autoreactive F1 B cells and for the development of the autoimmune syndrome occurring in this model. They also suggest that, although there is a marked depletion of H-2b-specific alloreactive CTL precursors in those neonatally tolerized mice, this state of tolerance can be associated with the persistence of H-2b-specific alloreactive CD4+ cells.

Specific neonatal induction of functional tolerance to allogeneic Mls determinants occurs intrathymically and the tolerant state is Mls haplotype-specific.

The studies described show that functional Mls specific tolerance, which we previously reported in peripheral spleen cells of mice injected within 24 h of birth with Mls incompatible spleen cells, is observable in the thymus on day 6. At this time a significant positive response is not detectable in spleen cells of normal mice. In the limiting dilution assay, we are able to detect a more profound depletion than others have found with anti-TCR antibodies. The tolerance in the thymus is not due to active suppression or simple dilution of responders by nonresponsive cells of the neonatal inoculum. By tolerizing BALB/c (Mls(b,c] mice with spleen cells from Mls(a) congenic mice, we show that Mls(a) incompatibility alone is sufficient for tolerance induction. Data from these experiments also show that the T cells seen responding at high frequency to stimulators from mice expressing Mls(a) determinants, as well as many other non-H-2 encoded incompatibilities, are indeed responding to Mls(a) determinants. In addition, experiments involving neonatal injection of Mls(b) mice with Mls(a) and Mls(c) spleen cells show no cross-reactivity of tolerance between Mls(a) and Mls(c) haplotypes. Our findings also show coexpression of determinants common to both Mls(a) and Mls(c) haplotypes by the Mls(d) haplotype. In all, the described experiments elucidate a pattern of Mls determinant specific hyporesponsiveness, in mice neonatally injected with appropriate allogeneic spleen cells, which bears all the hallmarks of functional, alloantigen specific, clonal deletion type tolerance.

Thrombocytopenia associated with the induction of neonatal tolerance to alloantigens: immunopathogenic mechanisms.

BALB/c mice rendered tolerant to alloantigens by neonatal injection of semi-allogeneic (C57BL/6 x BALB/c)F1 spleen cells develop a thrombocytopenia in association with an autoimmune lupus-like syndrome. The possible mechanisms involved in the thrombocytopenia were investigated. The development of thrombocytopenia was first detected at 3 weeks of age coinciding with the start of the other autoimmune manifestations and was always related to a state of tolerance and B cell chimerism. There was a significant increase of megakaryocytes in bone marrow and spleens from thrombocytopenic tolerant mice and radiolabeled platelets from these mice were more rapidly eliminated from the bloodstream than normal platelets when injected into normal recipients. A significant correlation between the spleen weight and the decrease of the circulating platelets was observed, although some mice with severe thrombocytopenia had only a moderate spleen enlargement. Thrombocytopenia significantly correlates with the levels of platelet-associated IgG (PAIgG) but not with anti-single-stranded DNA antibodies or circulating immune complexes. Platelets from mice with high levels of PAIgG had a shorter life-span when injected into normal mice than those from mice with low or normal PAIgG. The possibility that PAIgG are partially due to antibodies reacting specifically with platelet membrane components was analyzed. First, F(ab')2 Ig fragments from tolerant mice were shown to bind to normal platelets, in contrast to F(ab')2 Ig fragments from normal mice. Second, some monoclonal antibodies produced by hybridomas derived from tolerant mice reacted in vitro with platelets and induced a transient thrombocytopenia after i.v. injection into normal mice. These data suggest that the thrombocytopenia observed in tolerant mice is the result of a peripheral hyperdestruction of platelets associated with (a) hypersplenism, (b) nonspecific fixation of immunoglobulins, probably as immune complexes and (c) with autoantibodies reacting specifically with platelets. It may represent an interesting model for human chronic idiopathic thrombocytopenia.

Neonatal induction of allogeneic tolerance prevents T cell‐mediated autoimmunity in NOD mice

Diabetes in the NOD mouse strain is a genetically programmed T cell-mediated autoimmune process that is directed against an as yet unknown antigen target(s) on pancreatic beta cells. To investigate whether the course of the autoimmune disease could be altered by immune manipulations of the T cell repertoire, we have induced allogeneic tolerance by injecting F1 semiallogeneic spleen cells into NOD neonates. This procedure resulted in a significant protection against both insulitis and diabetes. However, although it requires the induction of tolerance, as shown by the failure of non-tolerizing irradiated cells to prevent autoimmunity, protection appeared to be independent of the major histocompatibility complex haplotypes of the F1 spleen cells injected at birth, e.g. (C57BL/6 x NOD)F1, (CBA/Ca x NOD)F1 or (BALB/c x NOD)F1 cells. In addition, a similar degree of protection was induced, whether the tolerant state, as assessed by mixed lymphocyte reaction studies in vitro, was of short duration, approximately 6 weeks, or lasted for more than 12 weeks. Putative veto or suppressor functions of chimeric T cells were ruled out, since mice tolerized with T cell-depleted F1 spleen cells were equally protected. We conclude that the expression of spontaneous T cell-mediated autoimmunity can be modulated by immune manipulations at birth. Whether the protection observed in the present experiments resulted from the production of one or several specific holes in the autoimmune T cell repertoire, i.e. cross-tolerance, or whether it resulted from nonspecific disturbances of the emerging T cell repertoire remains to be elucidated.

Neonatal tolerance induction to Mls a: I. Tolerance to Mls a is restricted by shared MHC determinants

In this paper we have examined the influence of MHC (major histocompatibility complex) on neonatal tolerance to Mls a (minor lymphocyte stimulating). By employing a novel approach we have shown that tolerance to Mls a is restricted by shared MHC determinants. Thus, neonatal Mls b mice, injected at birth with spleen cells from Mls a mice, were tested as adults for Mls a specific responses by interleukin-2 limiting dilution analysis, a technique which allows us to discriminate between responses to MHC + Mls a and to MHC alone. Tolerance to Mls a was in the context of any MHC type examined—donor, host, and third-party MHC products. These results show that tolerance to Mls a is restricted by shared MHC determinants and extend previous studies indicating that activation of Mls a responses is similarly restricted.

Intrathymic elimination of Mlsa-reactive (V beta 6+) cells during neonatal tolerance induction to Mlsa-encoded antigens.

The cellular basis of neonatally induced T cell tolerance has been investigated in a model system in which usage of a particular TCR V beta segment (V beta 6) is strongly correlated with reactivity to antigens encoded by the Mlsa genetic locus. Expression of V beta 6 by peripheral T cells was virtually abolished in BALB/c (H-2d, Mlsb) mice rendered neonatally tolerant to DBA/2 (H-2d, Mlsa) lymphoid cells, whereas control V beta 8-bearing T cells remained at near normal levels. Further analysis revealed that elimination of V beta 6+ T cells occurred in the thymus of neonatally tolerant mice and could not be explained by receptor modulation or T cell chimerism. These data thus support the clonal deletion model of tolerance induction.

Prevention of recurrent autoimmune diabetes in BB rats by anti-asialo-GM1 antibody.

BB rats exhibit a syndrome of spontaneous diabetes that has clinical and pathological characteristics analogous to those found in human insulin-dependent diabetes mellitus (IDDM). Islet tissue transplanted into spontaneously diabetic BB rats is uniformly destroyed by a recurrence of the autoimmune response that destroyed the diabetic subject's native islets. To examine recurrent autoimmune destruction of transplanted islets, it is necessary to exclude islet damage that might result from allograft rejection. We utilized neonatal tolerance induction to prevent rejection of Wistar-Furth (WF) (RT1u) islet allografts by spontaneously diabetic BB recipients. We determined that islet-recipient treatment with anti-asialo-GM1 (anti-AGM1) antibody prevents recurrent autoimmune diabetes that would otherwise destroy transplanted WF islet grafts. Anti-AGM1 therapy significantly decreased peripheral blood natural killer (NK) cell activity. These data suggest a role for NK cells in the pathogenesis of recurrent diabetes in neonatally tolerant BB rats.

Characterization of two molecules at 30,33 kDa as major target antigens of natural thymocytotoxic autoantibodies

We have attempted to characterize, by immunoblotting, the cell surface determinants which are recognized by natural thymocytotoxic autoantibodies (NTA). NTA-positive sera from spontaneously autoimmune mice and from mice rendered autoreactive by neonatal induction of tolerance were used as probes on blots of thymocytes. Fifty percent of the sera screened under these conditions reacted with a doublet of 30,33 kDa molecular weight present on membranes, but not detectable on blots of total cell extracts. Additional bands of various molecular weights were detected by NTA-positive sera at a much lower frequency than the 30,33 kDa determinants. Direct evidence of identity between the antibodies inducing thymocytotoxicity and those detecting the doublet in immunoblotting was provided by immunoadsorption tests. Among a panel of immunoadsorbents prepared with thymocyte membrane proteins of various molecular weights, only the one containing the 30,33 kDa molecules efficiently adsorbed cytotoxic antibodies whereas the other preparations containing some of the bands occasionally detected in immunoblotting had practically no effect. In addition we showed that the 30,33 kDa doublet is also detected on membrane preparations of T and B lymphocytes but not on preparations of a non-lymphoid cell line, and is composed of two independent molecules not covalently linked, in their native configuration, by disulfide bonds. Altogether these results strongly suggest that the 30,33 kDa molecules represent major cell surface determinants for thymocytotoxic autoantibodies.

Induction of transplantation tolerance by intraportal injection of allogeneic bone marrow cells: Possible implications for intrauterine bone marrow transplantation across major histocompatibility barriers

Abstract. Intraportal inoculation of C57BL/6 marrow cells into sublethally (400 rad) irradiated BALB/c recipients resulted in durable chimerism and the permanent acceptance of C57BL/6 skin allografts. Sublethally irradiated recipients of a similar number of marrow cells inoculated systemically did not develop chimerism or any significant prolongation of the survival of C57BL/6 skin allografts. Consequently, lethal graft-versus-host disease developed only in recipients of intraportal marrow allografts (80%). The intraportal injection of allogeneic C57BL/6 marrow cells into nonirradiated recipients resulted in significant, although not permanent, prolongation of skin allograft survival without durable chimerism, suggesting that the introduction of alloantigens intraportally may favor the induction of nonresponsiveness to alloantigens even across strong major histocompatibility barriers. The relevance of these findings is discussed regarding the intraportal inoculation of allogeneic bone marrow cells for the treatment of genetic disorders in utero through the induction of neonatal tolerance.

SUCCESSFUL INDUCTION OF SPECIFIC HYPOREACTIVITY TO RAT SKIN XENOGRAFTS IN NEWBORN MICE EFFECT OF IMMUNOREGULATORY MOLECULES

Inoculation of newborn mice with spleen and bone marrow cells from newborn (less than 24-hr-old) rat donors, as compared with cells from adult donors, resulted in induction of profound hyporeactivity or even long-lasting tolerance of skin xenografts. This tolerance was specific since skin allografts transplanted to tolerized mice simultaneously with specific rat grafts were rejected in normal fashion. Analysis of the reactivity in vitro in mixed lymphocyte culture and cytotoxicity assays revealed that cells from tolerant animals were specifically nonreactive to the tolerated xenogeneic antigens. Administration of active supernatants from cultures of concanavalin A-stimulated spleen cells from adult rats to tolerized mice within the first 5 days after birth impaired tolerance. The results show that the approach used is the first successful model of neonatal induction of tolerance to skin xenografts in mammals and emphasize the role of immunoregulatory factors in this process.

Autoimmune syndrome after induction of neonatal tolerance to alloantigens: effects of in vivo treatment with anti-T cell subset monoclonal antibodies.

BALB/c (H-2d) mice rendered tolerant to h-2b alloantigens by neonatal injection of semiallogeneic (C57BL/6 X BALB/c)F1 spleen cells develop autoimmune features due to an abnormal activation of persisting F1 donor B cells. The role of T cells in this autoimmune syndrome was studied by in vivo treatment of tolerant mice with anti-L3T4(GK-1.5) or anti-Ly-2 (H-35-17.2) monoclonal antibodies. The treatment of tolerant mice from day 2 to day 21 of life with anti-L3T4 MAb completely prevented the occurrence of circulating immune complexes of anti-ssDNA anti-Sm and anti-hapten (FITC) IgG antibodies as well as the glomerular deposition of Ig that were usually seen in untreated tolerant mice. This effect persisted for at least 6 wk after stopping this treatment. When the injections of anti-L3T4 MAb were delayed until day 15 of life, a very significant decrease of the autoimmune manifestations was still observed. Treatment of tolerant mice with anti-Ly-2 MAb during the same period had no effects on the autoimmune disease as compared with untreated tolerant mice. No effects on the maintenance of tolerance vs H-2b alloantigens were observed after treatment with anti-L3T4 MAb, as followed by the decrease of CTL and CTL-p alloreactivity and by the persistence of F1 donor B cells, indicated by the presence of Ig bearing the Ighb donor allotype. These results suggest the existence of interactions between L3T4+ T cells and persisting autoreactive B cells from F1 donor origin in the development of the autoimmune syndrome after neonatal induction of transplantation tolerance.

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens: III. Significance of hemopoietic stem cells for induction and maintenance of Mls tolerance by continuous supply of tolerance-inducing nonlymphocytes

The role of hemopoietic stem cells and of other cell types in the induction and maintenance of immunologic tolerance in the thymus was investigated by intravenous injection of Mls-semiallogeneic cells into newborn mice less than 24 hr after birth. Mls-specific tolerance was induced by inoculation of peritoneal cells and thymus cells, and the tolerant state was compared with that induced by bone marrow cells which had hemopoietic stem cell activity and were able to create a stable chimera in both central and peripheral lymphoid organs. When peritoneal or thymus cells were injected, the level of tolerance attained was proportional to the number of cells injected, though peritoneal cells were 20 times as effective as thymus cells. In vivo functions of tolerance-inducing cells and their immediate precursors were radiosensitive and belonged to a Thy-1 −, nylon-wool-nonadherent (probably non-B), weakly Sephadex G-10-adherent cell population. Tolerance induced by peritoneal cell injections was transient, starting to terminate within the first 2 weeks of life, while tolerance caused by bone marrow cell injections persisted through more than 6 weeks. Such transient tolerance induced by the former became long-lasting when followed by an additional injection of bone marrow cells, which did not cause thymic lymphocyte chimerism. All data indicated that bone marrow stem cells were engaged in tolerance induction and maintenance by continuously supplying tolerance-inducing nonlymphocytes.

Characterization of cytotoxic cells in mice rendered neonatally tolerant of MHC alloantigens: evidence for repertoire modification.

A common prediction of clonal deletion/inactivation hypotheses is that cells with high avidity for tolerogen are preferentially eliminated, with low avidity cells being most likely to escape the tolerance induction mechanism. Thus it would be expected that the tolerogen-specific cells in tolerant mice would have a different repertoire than those in normal mice. To find evidence in favor of this prediction, neonatal B10.A mice were rendered tolerant to B10 by the injection of 15 X 10(6) (B10.A X B10)F1 spleen and bone marrow cells, and tolerance was assessed by the acceptance of B10 skin grafts for greater than 50 days. Mice rendered tolerant in this manner contain severely reduced (to less than 10% of normal) but detectable numbers of tolerogen-specific cytotoxic cell precursors that can be activated in the presence, but not absence, of exogenous interleukin 2. Spleen cells from the tolerant animals were compared with those of normal B10.A mice with respect to the expression of differentiation markers on the surface of B10-specific cytotoxic cells and their precursors, and the relative strength of the anti-B10 response toward Kb and Db as a measure of the repertoire of the cytotoxic cell populations. The T cell nature of the tolerogen-specific cytotoxic cells in both normal and tolerant mice was confirmed by their susceptibility to lysis by anti-Thy-1 or Lyt-2 antibody and complement. More importantly, cold target inhibition experiments showed that cytotoxic T cells from tolerant mice were inhibited to a greater degree by B10.A(2R) (KkDb) cold targets than B10.A(5R) (KbDd), suggesting that the response was preferentially directed at the D end of H-2, in direct contrast to normal B10.A spleen cells, which show a preferential response against Kb. Measurement of the frequency of anti-Kb and anti-Db cytotoxic T cell precursors in the spleens of normal and tolerant mice confirmed the differential specificities seen in the cold target experiments. The data suggest that neonatal tolerance induction results in repertoire modification of the anti-tolerogen response rather than a uniform decrease in anti-tolerogen reactivity. Possible mechanisms to explain the alteration in the repertoire of tolerant mice are discussed.

Test of prolongation of skin graft survival by blood injections provides evidence for presence of a new histocompatibility locus in the B-G region of chicken MHC.

When used for pretransplantation treatment, blood of congenic chicken lines CB and CB.R1, incompatible only in the B-G region of the major histocompatibility complex (MHC), differed in their ability to induce prolonged survival of skin grafts transferred from either of these lines onto recipients of a third congenic line, CC. Moreover, skin grafts from CB and CB.R1 donors displayed a difference in survival time, irrespective of blood pretreatment. Graft survival time after pretreatment of recipients with CB blood could be prolonged by prior induction of neonatal tolerance to the B-G product; this could be done with injections of whole blood or of separated erythrocytes or leucocytes of line CC.R1 chickens (incompatible with CC recipients in the B-G region). The results indicate that a new histocompatibility locus is present in the B-G region of the chicken MHC.

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens. II. Significance of MHC antigens in anti-Mls tolerance.

Specificity of anti-Mlsa tolerance induced in BALB/c (H-2d, Mlsb) neonates was investigated by a popliteal lymph node (PLN)-swelling assay for the local graft-versus-host (GVH) reaction by injecting tolerant thymus cells into the footpads of several types of F1 hybrid mice. When thymus cells were obtained from 1-week-old normal BALB/c, they evoked enlargement of PLNs of (BALB/c X DBA/2)F1 (H-2d, Mlsb/a) [CDF1] recipients and of other hybrid recipients, heterozygous in Mlsa,c,d alleles, irrespective of the major histocompatibility complex (MHC) haplotypes. The same thymus cells did not cause the response in MHC-heterozygous F1 hybrids when the hybrids were homozygous in Mlsb, identical with BALB/c mice. Therefore, the PLN response to Mls antigens, known to be closely associated with MHC-class II antigens, was not directed to the class II antigens themselves. This enabled us to examine the effects of MHC on tolerance induction to the Mls antigens. When BALB/c neonates were injected with CDF1 bone marrow cells, complete tolerance to Mlsa-H-2d antigens of CDF1 cells was induced in the thymus, while responsiveness to Mlsa antigens in the context of H-2k and H-2b antigens, was not affected. This indicates MHC-restriction of neonatal tolerance to Mls antigens. Furthermore, when Mls and H-2-heterozygous (BALB/c X AKR)F1 (H-2d/k, Mlsb/a) bone marrow cells served as the tolerogen, thymus cells of BALB/c neonates were also tolerized to Mlsa-H-2k antigens as well as to Mlsa-H-2d antigens, which suggests the involvement of MHC, probably class II antigens of tolerance-inducing cells.

Neonatal tolerance induction in the thymus to MHC-class II-associated antigens. I. Preferential induction of tolerance to Mls antigens and resistance to allo-MHC antigens.

Neonatal tolerance inducibility of self-major histocompatibility complex (MHC)-class II-associated antigens was compared with that of allo-class II antigens. BALB/c (H-2d, Mlsb) mice, less than 24 hr after birth, were intravenously injected with bone marrow cells of either (BALB/c X DBA/2)F1 (H-2d, Mlsb/a, semiallogeneic at the Mls locus) or (BALB/c X B10.BR)F1 (H-2d/k, Mlsb; semiallogeneic at the MHC), as antigens. The mice were tested for in vivo immune activity of class II-reactive T cells by means of the popliteal lymph node-swelling assay. They developed tolerance, irrespective of type of antigens, showing profoundly suppressed host-versus-graft reaction, and those tolerized to the allo-MHC antigens accepted skin grafts of the corresponding allogeneic mice. In the thymus and spleen of the Mls-tolerant mice, antigen-specific class II-reactive T-cell activity was completely abolished, without the apparent involvement of suppressor cells. In contrast, the activity in allo-MHC-tolerant mice was not reduced in either thymus or peripheral lymphoid organs, suggesting that systemic hyporesponsiveness is attributable to reversible suppression of immune competent cells. The resistance for cell-level tolerance induction to allo-class II antigens may not be ascribed to the active participation of allo-MHC antigens in prevention of or in escape from tolerance induction or both, since an injection of bone marrow cells of both Mls and H-2-semiallogeneic (DBA/2 X B10.BR)F1 (H-2d/k, Mlsa/b) mice could induce tolerance to Mlsa-H-2d antigens in newborn thymus cells.

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.

Autoimmunity after induction of neonatal tolerance to alloantigens: role of B cell chimerism and F1 donor B cell activation.

BALB/c mice rendered tolerant by the neonatal injection of semiallogeneic (C57BL/6 X BALB/c)F1 spleen cells develop features of autoimmune disease. The possible mechanisms involved in autoantibody production, particularly anti-DNA antibodies, were investigated. In the first 5 wk, there was polyclonal B cell activation, as indicated by marked hypergammaglobulinemia, with a predominance of IgG1 and an increased production of antihapten antibodies. IgG1 anti-SSDNA and anti-DSDNA antibodies were detected with similar kinetics, but at higher titers than the anti-hapten antibodies. Also, there was a correlation between the effective induction of tolerance, as evaluated by the measurement of alloantigen-specific cytolytic T lymphocyte precursors, the persistence of B cell chimerism, and the production of anti-DNA antibodies. Anti-DNA antibodies were observed only in mice exhibiting a persistence of immunoglobulins bearing the donor's allotype. To determine the origin of anti-DNA antibodies, experiments were conducted whereby newborn BALB/c (Igh-1a) mice were injected with F1 cells from mice resulting from a crossing between Igh congenic BALB/c mice bearing the IgCHb allotype and conventional C57BL/6 mice (Igh-1b). All anti-DNA and anti-hapten antibodies exhibited the Igb allotype and thus were produced by the F1 donor B cells. The initial phase of tolerance induction was apparently associated with an allogeneic helper effect, because DNP-KLH-primed F1 donor cells transferred to newborn BALB/c could be stimulated after challenge with DNP-BGG. The triggering of persisting auto-reactive F1 donor B cells may reflect an activation by "incompletely" tolerant semiallogeneic T cells.

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.