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

The role of BCR isotype in B-cell development and activation

The development and function of B lymphocytes critically depend on the non-germline B-cell antigen receptor (BCR). In addition to the diverse antigen-recognition regions, whose coding sequences are generated by the somatic DNA rearrangement, the variety of the constant domains of the Heavy Chain (HC) portion contributes to the multiplicity of the BCR types. The functions of particular classes of the HC, particularly in the context of the membrane BCR, are not completely understood. The expression of the various classes of the HC correlates with the distinct stages of B-cell development, types of B-cell subsets, and their effector functions. In this chapter, we summarize and discuss the accumulated knowledge on the role of the μ, δ, and γ HC isotypes of the conventional and precursor BCR in B-cell differentiation, selection, and engagement with (auto)antigens.

Central B-cell tolerance: where selection begins

The development of an adaptive immune system based on the random generation of antigen receptors requires a stringent selection process that sifts through receptor specificities to remove those reacting with self-antigens. In the B-cell lineage, this selection process is first applied to IgM(+) immature B cells. By using increasingly sophisticated mouse models, investigators have identified the central tolerance mechanisms that negatively select autoreactive immature B cells and prevent inclusion of their antigen receptors into the peripheral B-cell pool. Additional studies have uncovered mechanisms that promote the differentiation of nonautoreactive immature B cells and their positive selection into the peripheral B-cell population. These mechanisms of central selection are fundamental to the generation of a naïve B-cell repertoire that is largely devoid of self-reactivity while capable of reacting with any foreign insult.

Regulatory B cells: evidence, developmental origin and population diversity

The adaptive immune system has developed several highly effective mechanisms in order to avoid excessive or unwanted reactions and promote resolution of immune activation. An emerging, significant body of evidence indicates that B cells can actively modulate immune responses by mechanisms that do not directly involve the production of antibodies. B cells appear to have the capacity to both induce and suppress immune effector mechanisms and they exert these functions both by contact-dependent interactions and through the secretion of cytokines. In this review we will focus on the regulatory suppressive function of several recently described B cell populations, functionally defined "regulatory B cells" or Breg cells. We will first outline the evidence that has led to their identification and then we will summarize current hypotheses on their ontogeny and possible lineage relationship.

Role of Maternal Ig in the Induction of Cκ-Specific CD8+ T Cell Tolerance

Although the influence of maternal Ig on the B cell repertoire and subsequent Ab response has been extensively studied, much less attention has been devoted to their effects on T cell responses of the offspring. To address this question, we have studied the influence of maternal κ-positive Ig (Igκ) on the Cκ-specific CD8+ T cell response of κ knock-out (κ−/−) pups resulting from various crosses and foster nursings. These systems allowed control of physiologic transmission of Igκ at defined periods of ontogeny. Our data show that conventional transfer of maternal Ig via the placenta plus colostrum/milk or adoptive transfer via only the colostrum/milk were the most efficient at tolerizing Cκ-specific CD8+ responses. Surprisingly, tolerance was not detected in κ−/− pups born to κ+/− females obtained by cesarean delivery and suckled by κ−/− mothers (transplacental supply only). Tolerance, which was strong until 5 wk of age, was reversible and waned with the decrease of Igκ serum concentration. Depletion of CD4+ T cells at the time of Cκ peptide immunization abolished the tolerance of Cκ-specific CD8+ T cells. These data suggest that an oral supply of Ig is very efficient at inducing and maintaining tolerance of Cκ-specific CD8+ T cells, at least for several weeks after birth, and that suppression rather than deletion is responsible for this tolerance. In addition, they strengthen the view that tolerance of CD8+ T cells to a soluble Ag is never permanently acquired even if it is present in large quantities during ontogeny.

The repertoire of serum IgM in normal mice is largely independent of external antigenic contact

Antigen-free (AGF) and germ-free (GF) mice, although essentially free of serum IgG, maintain normal levels of circulating IgM. Using a quantitative immunoblot assay, we have now analyzed the repertoire of serum IgM from AGF, GF, and specific pathogen-free (SPF) BALB/c mice, on large panels of natural antigens from homologous tissues and bacteria. The reactivity profiles were very similar in the three groups of mice. Multiparametric statistic evaluation of the data showed that BALB/c animals, SPF, GF, and AGF mice constitute an homogeneous group with similar immunoreactivity profiles when compared to C57BL/6. Differences between immunoreactivity profiles of GF and AGF mice were observed, but were not statistically significant. These results suggest that the serum IgM repertoire of normal mice is strictly regulated and selected by endogenous ligands.

On the maternal transmission of immunity: a 'molecular attention' hypothesis

Maternally-derived antibodies can provide passive protection to their offspring. More subtle phenomena associated with maternal antibodies concern their influence in shaping the immune repertoire and priming the neonatal immune response. These phenomena suggest that maternal antibodies play a role in the education of the neonatal immune system. The educational effects are thought to be mediated by idiotypic interactions among antibodies and B cells in the context of an idiotypic network. This paper proposes that maternal antibodies trigger localized idiotypic network activity that serves to amplify and translate information concerning the molecular shapes of potential antigens. The triggering molecular signals are contained in the binding regions of the antibody molecules. These antibodies form complexes and are taken up by antigen presenting cells or retained by follicular dendritic cells and thereby incorporated into more traditional cellular immune memory mechanisms. This mechanism for maternal transmission of immunity is termed the molecular attention hypothesis and is contrasted to the dynamic memory hypothesis. Experiments are proposed that may help indicate which models are more appropriate and will further our understanding of these intriguing natural phenomena. Finally, analogies are drawn to attention in neural systems.

Modulation of immune response to Lol p I by pretreatment with anti-idiotypic antibody is not restricted to the idiotypic expression

To study the role of anti-idiotypic antibodies in the regulation of the immune response to Lol p I (the major allergenic component of rye grass pollen), we have recently generated a panel of three MoAbs directed against distinct epitopes of Lolp I and an anti-idiotypic MoAb directed against the idiotype borne by one of the anti-Lol p I MoAbs (290A-167). The effects of pretreatment with this anti-idiotypic MoAb in BALB/c mice before immunization with the antigen have been examined. The anti-idiotypic MoAb or unrelated MoAb were given weekly for 8 weeks intraperitoneally. Mice then received the antigen (2 micrograms) adsorbed with alum (2 mg) at weeks 9, 11 and 13. Serum anti-Lol p I antibodies (IgG or IgE) and specific idiotypic responses were measured. Anti-Lol p I IgG antibodies could be detected before immunization with Lol p I only in mice pretreated with anti-idiotypic MoAb. Immunization with Lol p I induced an anti-Lol p I IgG response in both groups, but this response was higher in mice that received anti-idiotypic MoAb. Similar profiles were seen for specific IgE antibodies and idiotypic responses. Surprisingly, idiotypes borne by other anti-Lol p I MoAbs (539A-6 and 348A-6) had also been enhanced after pretreatment with the anti-290A-167 MoAb. These observations suggested that the pretreatment with this anti-idiotypic MoAb modulates not only the expression of the respective idiotype, but also affects other idiotype responses.

Characterization of idiotype-specific I-Ed-restricted T suppressor lymphocytes which confine immunoglobulin class expression to IgM in the anti-alpha (1- > 3) Dextran B 1355 S response of BALB/c mice

The humoral immune response of conventionally raised BALB/c mice to the so-called "thymus independent" antigen alpha (1- > 3) Dextran B 1355 S (Dex) is predominantly of the IgM class. The response is further characterized by Igha allotype linkage and the dominance of the public idiotypes (Id) J558 and MOPC 104. In germfree raised BALB/c and in BALB/c nu/nu mice immunized with the same antigen an additional IgG response of the public Id is observed. Analysis of the regulation of the class expression reveals existence of specific Ts cells in euthymic mice which must have been activated pre- or perinatally by exposure to environmental bacterial antigens. They permit or enforce differentiation of Dex-specific B cells into B gamma memory cells without allowing further development into IgG producing plasma cells. An analogue of these splenic Ts cells has now been cloned and identified as an I-Ed restricted Id-specific T cell with exactly the properties ascribed above to the splenic Ts cells. This paper describes phenotypical and functional properties of the Ts cell clone 178-4. It evaluates this clone's role in controlling efficient anti-bacterial IgM-mediated immunity under conditions where a class switch to IgG antibody production is actively suppressed; possibly as a measure to avoid hazardous autoimmune reactions on the basis of crossreaction and antigenic mimicry between polysaccharide antigens.

In vivo effects of neonatal administration of antiidiotype antibodies on experimental autoimmune myasthenia gravis

The in vivo effects of neonatal administration of varying doses of anti-idiotype antibodies on serum anti-acetylcholine receptor (AChR) antibody titers, idiotype expression, and disease severity was studied in experimental autoimmune myasthenia gravis. Polyclonal affinity purified anti-idiotype antibodies and monoclonal anti-idiotype antibodies directed at anti-AChR monoclonal antibody 65 were administered in dosages varying from the nanogram to the microgram range. Mab 65 is directed against the main immunogenic region of mammalian AChR. In 1 out of 4 experiments administration of a nanogram dosage of anti-idiotype antibodies led to an enhanced anti-AChR antibody response after immunization with AChR. But no enhancing effect on idiotype expression could be demonstrated during this experiment. Adoptive transfer of spleen cells from rats pretreated with a nanogram dosage of anti-idiotype antibodies resulted in an significantly increased antibody response against rat AChR after immunization. From these experiments we conclude that in vivo administration of polyclonal or monoclonal anti-idiotypes does not reproduceably modify the serum antibody level against the acetylcholine receptor, nor influences the idiotype profile of the immune response. Secondly, the idiotype mediated manipulation of the immune response against large antigens, like the acetylcholine receptor, is clearly more complicated than that against small haptens. Adoptive transfer models, might be helpful in analysing the possibilities of anti-idiotype treatment in myasthenia gravis in more detail.

Inhibition of offspring response to HEL-CFA by administration of anti-HEL MAB to the mother is not related to the predominant idiotype, IdXE, or specificity of the MAB

In the neonatal suckling mouse, the antibody response to HEL-CFA can be inhibited by administration of certain anti-HEL monoclonal antibodies to the mother. The murine primary response to hen egg-white lysozyme (HEL), which can be elicited in A/J mice as early as 7 days of age, is characterized by a predominant specificity that includes the 3 N-terminal amino acids of HEL (TIP-dependence) and by a predominant idiotype, IdXE. A panel of murine IgG1 anti-HEL mAbs was administered to the suckling offspring via the mother. These mAbs were not equivalent in their effects on the offspring. Only two of six IgG1 mAbs, 2F4/2E5 (IdXE-positive, TIP-dependent) and 2D1 (IdXE-negative, TIP-independent), consistently induced suppression of the response of A/J offspring when immunized at 16-20 days of age with HEL-CFA. Suppression averaged 71% for 2F4/2E5 and 74% for 2D1 and was always statistically significant (P less than .05) when 275 micrograms mAb was administered IP to the mother within 24 hr postpartum. Since 2D1 is IdXE-negative and TIP-independent, neither of these properties appears to be crucial for suppression. Differences in transfer of the mAbs from the mother to the offspring or differences in catabolism of the mAbs in the offspring were not detected. When various characteristics of the mAbs such as affinity, idiotypy, and fine specificity were considered, there was no single factor which determined suppression. One of the two mAbs that suppressed the offspring response, 2D1, is idiotypically highly connected in the anti-HEL mAb panel. This observation suggests that idiotypic interactions in the developing neonatal repertoire with subsequent perturbation of T and B cell repertoire development may be an area for future investigation.

Therapeutic treatment of New Zealand mouse disease by a limited number of anti-idiotypic antibodies conjugated with neocarzinostatin

-81 and NE-1 idiotypes (Id) of human nephritogenic anti-DNA antibodies are interspecies Id expressed also in NZB/W F1 mice. We tried to manipulate the synthesis of spontaneously occurring anti-DNA antibody using monoclonal anti-Id antibodies (D1E2 and 1F5) conjugated with a cytotoxic agent, neocarzinostatin (NCS). In vivo administration of anti-Id antibodies conjugated with NCS brought about an improvement in the survival rate of female NZB/W F1 mice. It also caused a retardation of development of lupus nephritis and decreased the numbers of anti-DNA-producing cells. The suppression of anti-DNA antibody synthesis was specific and Id-mediated. The results indicate that the use of a limited number of anti-Id antibodies in combination with a cytotoxic agent may be applicable therapeutically to autoimmune diseases.

Two types of mu chain complexes are expressed during differentiation from pre-B to mature B cells

Immunoglobulin mu chains synthesized in murine pre-B cells are known to be associated with surrogate light chains designated as omega (omega), iota (iota) and B34. In addition to these molecules, we identified the complexes of polypeptides (50, 40, 27 and 15.5 kd) associated with surface or intracellular mu chains of pre-B cell lines. Most of these polypeptides were continuously synthesized and associated with mu chains in virgin B cells lines, although some of them scarcely bound to the mu kappa dimer or mu 2 kappa 2 tetramer concomitantly present in the same clone or population. However, in mature B cells they were no longer detectable except B34. Cross-linking of micron chains on the surface of pre-B cells resulted in an increase in intracellular free Ca2+, indicating that the micron chain complex on the surface of pre-B cell lines acted as a signal transduction molecule. However, the receptor cross-linkage of pre-B cell lines did not induce the increased inositol phospholipid metabolism usually observed in virgin and mature B cell lines. These results suggest that, during the differentiation from pre-B to mature B cells, the cells express two types of mu chain complexes which exhibit different structures as a whole and possess different signal transducing capacities.

Comparison between thymus- and spleen-derived B-cell hybridomas

When fusing thymocytes and spleen cells (SC) of 7- and 28-day-old BALB/c mice with Sp2/0, comparable numbers of clones were obtained. Immunoglobulin secretion was observed in 53-79% of splenic, but only 10-18% of thymic hybridomas. This was irrespective of tolerization through prenatal treatment with trinitrobenzenesulphonic acid (TNBS). Differences between control and tolerant mice were observed with respect to the frequency of anti-trinitrophenol (TNP)-producing hybridomas: in 7-day-old tolerant litters their frequency was increased in thymus and spleen as compared with controls, but it was decreased in 28-day-old tolerant mice. It is concluded that the majority of thymic B cells are in an activated, but non-producing state and that the repertoire of thymic B cells is influenced by prenatal contact with nominal antigen.

Donor Igh-linked genetic control of allotype-specific antibody response

Immunogenicity of allogeneic immunoglobulins in mice were studied, measuring the allotype-specific antibody activity by agglutination of allogeneic antibody-coated red blood cells. It was found that the serum from C.B-20 mice (Ighb, BALB/c-congenic) was uniquely immunogenic in BALB/c mice for allotype antibody response. Whereas the C57BL/6 (Ighb) serum was immunogenic only when heat aggregated and/or combined with adjuvant, the ultracentrifugation-deaggregated C.B-20 serum was definitely immunogenic when administered in a moderate dose (100 microliters/mouse). Even more surprising was the fast that very low doses (0.01-0.1 microliter) of soluble C.B-20 serum, but not C57BL/6 serum, down regulated the allotype-specific response effectively. Genetic analysis on congenic mice suggested that the immunogenicity is controlled by donor Igh or Igh-V (Id-C.B) inasmuch as the serum from BALB/c-congenic C.B-20 (Igh-VbCb), but not BALB/c-congenic BAB/14 (Igh-VaCb), mice was active in BALB/c mice in soluble form. Further studies showed that the Id-C.B was dominantly expressed on the immunoglobulins of (BALB/c x C.B-20)F1 and (C56BL/6 X C.B-20)F1 strains, and was originally derived from the C57BL/Ka strain. The major determinant for the antibody production was encoded in Igh-C, but not in Igh-V. It is suggested that Id-C.B controls the allotype-specific antibody response in an unusual manner, possibly acting as a unique determinant activating helper T cells.

The analysis of immature lymphoid precursors stored in longterm bone marrow culture

The long-term bone marrow culture system developed by Dexter (MBMC) is known to store immature lymphoid precursors capable of differentiating into mature B cells in irradiated or immunodeficient mice. It has been suggested that pre-B cells are not generated under such culture conditions, but that opinion was not based on any systematic analyses. In the present study under carefully controlled conditions, we observed that pre-B and pro-B cells were eliminated from the late stage of primary MBMC, and the former were not generated in recharged MBMC. Under appropriate conditions, these immature precursors in recharged MBMC generated in vitro immunoglobulin-positive (Ig+) cells to differentiate into antibody-forming cells upon stimulation with lipopolysaccharide (LPS). LPS-reactive B cells were observed in every 10th of the Ig+ cells, the frequency being essentially the same as that observed in normal B cells in different tissues. The immature B cell precursors generating LPS reactive cells were expressed in recharged MBMC at the frequency of 4.2 x 10(-6). A staining experiment showed that cells bearing AA4.1 were stored at the frequency of 10(-4)-10(-5). This frequency is thought to be similar to that of lymphoid precursors in recharged MBMC committed to differentiate along B lineage cells. Based on these results, we discussed the stage, nature, and mode of differentiation of immature lymphoid precursors stored in MBMC.

Effect of neonatal injection with antibodies to Leishmania mexicana on its growth in adult infected mice

Mice inoculated with monoclonal antibodies (MAb) directed to Leishmania mexicana antigens were not protected from growth of a subsequent challenge infection; this was the case even when those antibodies were capable of inhibiting parasite growth in vitro. However F(ab')2 fragments of one antibody (1E1) were protective in vivo. When neonatal mice were injected with MAb and subsequently infected as adults, the animals were more susceptible to parasite growth than uninjected controls. This increased susceptibility could be adoptively transferred with Lyt-1+ cells. Separate groups of animals were immunized with different MAb to L. mexicana, and parasite growth in these animals was studied. In no case was parasite growth altered, though these mice did produce specific antibodies directed against the immunizing MAb (anti-idiotypic antibodies). When neonatal mice were injected with these latter reagents, they were found to be more resistant to challenge infection than control animals. This resistance was associated with an enhanced ability of spleen cells from these mice to produce, on stimulation with parasite antigens in vitro, a factor rendering normal macrophages cytocidal for L. mexicana.

Maternal autoimmune disease influences self-tolerance in offspring: the role of suppressor cells and materno-foetal cell traffic

Autoimmune haemolytic anaemia (AIHA) was induced in normal strain (CBA/Ca/T6) mice by repeated intraperitoneal injection of rat red blood cells (RRBC). Antibody production to cross-reactive antigens on mouse red blood cells (MRBC) and foreign antigens on RRBC was measured by the direct antiglobulin test (DGAT) and serum haemagglutination, respectively. RRBC primed female or male mice and sheep red blood cell (SRBC) primed controls were mated with naive partners and their progeny immunized with RRBC in adult life. The offspring of mothers but not fathers with active autoimmune disease showed a significant reduction in antibody response to self (MRBC) antigens, whereas the response to non-self (RRBC) was unaffected. Transfer of 30 X 10(6) spleen cells from the progeny of RRBC primed mothers into non-irradiated normal recipients resulted in selective suppression of the anti-self response following challenge with RRBC, provided that the cell donors had been boosted with RRBC 7-10 days before the transfer was performed. Thus the progeny of mothers with AIHA possessed self-reactive memory suppressor cells (Ts) shown previously to belong to the Thy-1+ I-J+ Ly-2+ T cell subset in this model. To test whether the Ts were of maternal or foetal origin the suppressor assay was repeated with spleen cells from the F1 offspring of RRBC primed B10.A(3R) (I-Jb) mothers and normal CBA(I-Jk) fathers. Pretreatment with anti-I-Jb serum plus complement completely abrogated suppression on adoptive transfer but anti-I-Jk serum failed to do so, indicating that the Ts were derived from the mothers. These findings emphasize the potential importance of Ts in induction of self tolerance during early ontogeny.

Hyperreactivity of adult BALB/c mice tolerized at birth with TNP-ovalbumin

BALB/c mice injected with 0.2 mg TNP-ovalbumin (OA) within 24 hours after birth showed reduced levels of functionally active TNP-specific B cells and, accordingly, of plaque-forming cells (PFC) after challenge with carrier-bound TNP until the age of 8 weeks. Yet, when B cells of tolerized mice were cultured in the absence of antigen, a significant number of anti-TNP PFC were detected. Challenge of neonatally tolerized mice at older age with T-dependent or T-independent antigens led to a continuously increasing response towards TNP, which was dominated by IgG-producing B cells. At the age of 8 months, a five-fold augmentation of TNP-specific B cells and of anti-TNP antibodies (AB), as compared to animals treated accordingly as adults, was observed. Clonal analysis of regulatory cells revealed 2 populations of helper (Th1 and Th2) and suppressor (Ts1 and Ts2) T cells in spleen cells (SC) of tolerized mice. In SC of mice immunized as adults, Th1 and Th2, but only one Ts populations were observed. The frequencies of Th1 and Ts1 were in the same range in animals immunized neonatally or as adults. After challenge, frequencies of regulatory cells remained constant in animals immunized as adults. But, in neonatally tolerized mice, challenge resulted in increased frequencies of Th1 and Th2; Ts1 remained constant, and concomitantly the frequency of Ts2 declined significantly. The data are interpreted as newborn tolerance being due to transient B cell anergy via receptor blockade as well as inactivation of AB-producing cells. Neither deficiency in TNP-specific help nor dominance of TNP-specific suppression is involved in maintainance of tolerance, but tolerance appears to be sustained by interference of TNP-specific regulatory cells with anti-idiotypic regulatory cells (Th2, Ts2). Supposing a system of circular network interactions, activation of anti-idiotypic clones will be counterregulated/balanced by activation of antigen-specific clones. Thus, decreasing idiotypic connectivity during life may result in overshooting reactivity of neonatally tolerized mice at older age.

In vivo generation and function of B cells in the presence of a monoclonal anti-IgM antibody: implications for B cell tolerance

C57BL/6 mice were chronically treated with milligram doses of the noncytotoxic monoclonal anti-mu b antibody MB86 (IgG1, kappa) from birth or from fetal life. The spleens of the manipulated animals contained large numbers (25% as compared to control mice) of B lineage cells which expressed IgMb on the surface after overnight incubation in vitro. The spleens also contained B cells whose surface IgM was unreactive with antibody MB86. A few such cells were immortalized by cell fusion. They included cells secreting mu together with lambda 2 chains which apparently prevent recognition by antibody MB86, and a point mutant in the first constant domain of the mu chain, changing the b to the a allotype. Cells expressing MB86- surface IgM did not selectively expand under MB86 treatment over the first few months of life. Serum Ig levels in the manipulated mice were normal except for IgM which was undetectable in most instances. In some animals low levels of MB86- IgM molecules were produced. At 7 weeks of age, mice treated with MB86 from birth produced normal-size IgG anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) responses with the usual predominance of lambda 1 chain-bearing IgG1 antibodies. At the age of 5-6 months, and also in young mice treated with MB86 from fetal life, the responses were variable and presumably oligoclonal, with a tendency towards the production of antibodies with gamma 3 heavy and lambda 2 or lambda 3 light chains. We interpret these results to mean that B cells hit by antibody MB86 from the time of their generation become unresponsive to T cell-dependent stimulation, but are still able to expand. Occasionally, they escape functional suppression through class switching (to IgG3) upon mitogenic stimulation. At birth, C57BL/6 mice contain a mature B cell population which mediates normal immune responses under MB86 treatment and eventually dies out. Taken as a model of tolerance induction in B cells, the data provide evidence for "tolerant" cells and support the concept of an early phase of sensitivity to tolerance induction in B cell differentiation. The anti-NP response under MB86 treatment differed profoundly from control responses in idiotypic terms, but became normal as the animals recovered from suppression. This may reflect blockade by MB86 of idiotypic selection within the B cell population.

Analysis of somatic mutation and class switching in naive and memory B cells generating adoptive primary and secondary responses

Clonal progeny of naive B cells (producing a primary antibody response) and of memory B cells (producing a secondary response) were identified in a cell transfer system. Primary response clones are typically derived from IgM precursors and express unmutated V regions. Multiple isotype switches occur in these clones. Secondary response clones derive from IgG1 precursors and express highly mutated V regions. Additional switches do not occur. With one exception, there was no evidence for somatic mutation during clonal expansion. The generation of mutated memory cells may thus represent a distinct differentiation pathway. Evidence is presented that, in this pathway, mutants that have lost antigen binding specificity but that remain available for stimulation by a different antigen arise upon antigenic stimulation.

T-independent form of azophenylarsonate fails to reveal "silent" idiotype-positive B cells in idiotype-suppressed mice

In three distinct chronic Ig-specific suppression systems in which suppression was initiated by injection of mice with anti-idiotype (Id) or anti-allotype sera, evidence has been presented by others that the differentiation of B cells bearing surface Ig with a target marker (Id or allotype) need not be totally disrupted. Normally "silent" Id+ B cells from Id-suppressed mice could be revealed by certain procedures, one of these being to make use of the powerful stimulatory properties of bacterial lipopolysaccharide. We have employed a similar strategy to determine whether cryptic CRIA+ B cells exist in significant numbers in hyperimmune, CRI-suppressed (HIS) A/J mice. Thus, following T cell removal, the Ar-specific B cell repertoire from HIS mice was probed using Ar- Brucella abortus as a T-independent Ag. No evidence for "silent" CRIA+ B cells was found. The results, taken in conjunction with those of others, suggests that there may exist multiple forms of long-term Ig-specific suppression.

Isogeneic monoclonal antibodies against anti-alpha(1----3)dextran idiotypes. II. Neonatally induced idiotope-specific suppression: a comparative analysis

From a panel of isogeneic monoclonal anti-idiotope antibodies several were used as agents in neonatal idiotope suppression. They differed from one another in isotype, and in idiotope specificity, as described in the preceding report (Eur. J. Immunol. 1987. 17: 255). In their effects they were compared with respect to the following variables: minimum dose required for suppression; duration of suppression, and its relationship to the dose applied neonatally; half-life of anti-idiotope in the immune system of the young mice; specificity of suppression as achieved by a given anti-idiotope: in how far does it affect idiotopes defined by alternate anti-idiotopes? The following results were obtained: the minimum effective dose varied widely between anti-idiotopes. One, belonging to the IgM class, was completely ineffective; others varied from approximately 10 micrograms/mouse, required for complete suppression, to approximately 100 micrograms/mouse. The dose-response characteristic was independent of whether the state of suppression was tested (by immunization against alpha(1----3)dextran) 26 days or 70 days after neonatal anti-idiotope treatment. We take this as an indication that the anti-idiotope effect occurs during an early postnatal period. There appeared to be a relationship between the rate of decay of anti-idiotope in the system and the dose required for complete suppression: the faster the decay, the more is needed initially. The persistence of effective molecules in the animals appears to depend on their isotype (as has been noted by others before): IgM decays fastest, and was ineffective in our experiments; IgG1 stays longest, and the smallest dose was required for suppression. IgG2b was intermediate. The specificity of neonatal suppression was clearly correlated with the serological specificity of the anti-idiotope monoclonal antibodies, as well as with the representation of the corresponding idiotopes in physiological anti-dextran sera, as described in the preceding report: private anti-idiotopes suppressed their counterpart idiotopes only, while the public anti-idiotope suppressed all other idiotopes in concert.

Induction of chronic idiotype suppression by ligands binding to the variable (not the constant) region of the idiotypic target

It was previously shown that in C57BL/6 mice chronic suppression of an idiotypically defined subset of lambda 1 chain-bearing anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibodies is achieved by neonatal administration of allogeneic monoclonal anti-idiotope antibodies reactive with this subset, or by NP coupled to mouse immunoglobulin. The present data show that isologous monoclonal anti-idiotope antibodies have the same effect. In contrast, antibodies against constant region determinants of lambda 1, mu or delta immunoglobulin chains failed to induce chronic suppression of the same antibody subset. Furthermore, the effect of the anti-idiotope antibodies was neutralized by idiotypic antibodies of the IgG1 class, injected before or together with the anti-idiotype. These results suggest that the mere complexing of idiotypic molecules on the B cell surface or in the circulation is insufficient for the induction of chronic idiotype suppression. In the present system, induction appears to require the binding of a ligand to idiotype-bearing receptor V regions, expressed on the surface of B (or T?) cells.

The molecular evolution of the immune response: idiotope-specific suppression indicates that B cells express germ-line-encoded V genes prior to antigenic stimulation

Antibodies expressed by the immune B cell population are characterized by variable region amino acid substitutions resulting from somatic nucleotide replacement (somatic mutation). This is not true of antibodies expressed by the "naive" B cell population. It is at present unclear whether this discrepancy is due to the preferential clonal selection of a pre-existing subpopulation of naive B cells that express variable regions altered via nucleotide replacement, or whether the process of nucleotide replacement occurs only during the antigen-dependent stages of B cell differentiation. To address this question we have used anti-idiotypic suppression to functionally delete B cells that express particular variable-region structures from the antigen-responsive repertoire. Suppression of the major cross-reactive idiotype (IdCR) expressed in strain A mice in response to p-azophenylarsonate (Ars) was induced using the monoclonal anti-IdCR antibody AD8. The idiotope recognized by AD8 is easily destroyed by alteration of IdCR variable-region structure via nucleotide replacement. The IdCR anti-Ars immune repertoire is characterized by antibodies that lack the AD8-cognate idiotope due to nucleotide replacement. However, complete suppression of the IdCR could reproducibly be achieved by administration of AD8 prior to Ars immunization. This result indicates that all IdCR-expressing B cells also express the AD8-cognate idiotope prior to immunization. Thus, somatic nucleotide replacement must occur exclusively during the antigen-dependent stages of B cell differentiation in this system.

Clonal recruitment and somatic mutation in the generation of immunological memory to the hapten NP

The nucleotide sequences of the variable regions of lambda 1 chain bearing anti-NP antibodies from the secondary response of C57BL/6 mice were determined. The data indicate that the V186.2 VH gene which dominates the primary anti-NP response is expressed in nine out of 10 secondary response antibodies and is extensively mutated. In the V lambda 1 regions somatic mutations are less frequent. While point mutations predominate, there is suggestive evidence for two conversion events, one involving a one-codon deletion. Most, but not all, secondary response antibodies have a higher affinity (up to 10-fold) for the hapten than is seen in the primary response. The increase in affinity correlates with 'parallel' mutations in CDRs of H and L chains, likely to play a role in hapten binding. The analysis of VDJH rearrangements demonstrates that the secondary response lambda 1 chain-bearing antibodies are produced by a diverse set of B cell clones, which are only rarely expressed in primary responses. These clones are characterized by N-sequence-mediated heterogeneity in the 3' half of CDR3, where the germ line sequence of the D element DFl16.1 predominates in primary response antibodies. The antibodies analyzed in this and in previous work were isolated from idiotypically suppressed mice in order to evaluate whether, intraclonally, idiotype suppression selects antibody mutants into the memory pool, through suppression of the wild-type. A selection of this type was not detectable. However, idiotype suppression may control the pattern of clonotypes expressed in the primary versus the secondary response.

The T lymphocyte response to syngeneic lambda 2 light chain idiotopes. Significance of individual amino acids revealed by variant lambda 2 chains and idiotope-mimicking chemically synthesized peptides

In the present study we have investigated the structure of the helper T cell (Th)-defined idiotope (Id) of myeloma protein 315 lambda 2 light chain (lambda 2(315] in BALB/c (H-2d) mice which carry a high-responder immune response gene for this Id. Three peptides were synthesized which spanned the third hypervariable region (HV3) of lambda 2(315): peptides 88-99, 94-108 and 91-108. Only peptide 91-108 was capable of eliciting carrier-specific Th that recognized M315 or free lambda 2(315). These Th did not recognize lambda 2(5-7) chain which differs from lambda 2(315) at 4 positions in this region; these are Tyr94, Ser95, Thr96, Tyr98 for lambda 2(5-7) and Phe94, Arg95, Asn96, Phe98 for lambda 2(315). Immunization with peptide analogues revealed that substitution of Tyr for Phe94 was compatible with Id-lambda 2(315) mimicry, but substitution of Ser for Arg95 or Thr for Asn96 destroyed the Th-recognized Id. Furthermore, Th primed with lambda 2(5-7) chain did not cross-react with lambda 2T952; these lambda 2 chains only differ from each other at positions 98 and 99 at the V lambda 2-J lambda 2 junction. The data indicate that individual amino acids of short peptide segments are critical for Th-recognized Id of the lambda 2 HV3 loop and V lambda 2-J lambda 2 junction. Furthermore, the immunogenicity of a small peptide suggests that the carrier (lambda 2)-specific Th recognize Id that have been processed by antigen-presenting cells (APC). This implies the existence of two categories of "internal images" of foreign or of self antigens: (a) serologically defined and (b) T lymphocyte defined. We propose that as a rule, Id processing by APC, including B cells, destroys the first and reveals the second category. The possible physiological function of these Id-specific T cells in network interactions with B cells is discussed.

Helper T cells reacting to idiotype on IgG but not IgM

Immunization with an IgG1 but not an IgM monoclonal anti-NP (4-hydroxy-3-nitrophenyl acetyl) antibody induced idiotype-recognizing T helper cells, although these two antibodies carry the same variable regions. The T cells appear to react to an idiotype on the IgG1 but not the IgM antibody. They selectively enhance the expression of that idiotype in the IgG1 fraction of an in vitro anti-NP response.

Thymus-independent induction of idiotype suppression in newborn mice by syngeneic anti-idiotype antisera

BALB/c and BALB/c nu/nu mice were shown to express to a variable extent in their response against dextran B1355S (Dex), an idiotype which is present on the Dex-reactive BALB/c myeloma protein MOPC 104E. Injection of minute amounts of syngeneic anti-MOPC 104E idiotype antisera into neonatal euthymic or athymic BALB/c mice suppressed this idiotype in the Dex-specific response of the adult animals. When spleen cells from suppressed BALB/c mice were transferred into irradiated BALB Ighb mice the state of suppression persisted. Data are discussed with respect to possible mechanisms regulating expression of this idiotype.

Antigen induces chronic idiotype suppression

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

Structure of primary anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibodies in normal and idiotypically suppressed C57BL/6 mice

Eight monoclonal antibodies from the primary response of C57BL/6 mice against the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) were isolated. The antibodies carry lambda 1 light chains and have similar affinities for the immunizing hapten. Sequence analysis at the level of mRNA reveals that all antibodies express the VH gene 186.2 and all but one the DFl 16.1 gene segment. The J segment of the heavy chain is JH2 in six cases and JH4 in two. Somatic point mutations are scarcely detectable in the antibodies, but there is extensive sequence variability at the boundaries of the D gene segment, mainly at its 5' end. However, seven of eight antibodies express tyrosine in position 99 of the heavy chain, encoded either by the 5' codon of DFl 16.1 or by presumed N sequences. In the former case, the tyrosine is the first of a stretch of three (positions 99-101). In the latter, a similar stretch (positions 99, 101, 102) is interrupted by aspartic acid, asparagine or cysteine in position 100. These variations profoundly affect idiotypic specificity. Six of the eight monoclonal antibodies came from mice neonatally suppressed by an anti-idiotope antibody whose target idiotope is regularly expressed in primary anti-NP responses and depends upon a non-germ-line-encoded aspartic acid in position 100 of the heavy chain. The sequence data show that the mice circumvent suppression by expressing antibodies which lack this aspartic acid but are otherwise structurally very similar to anti-NP antibodies from normal animals. Since suppression in the animals is partly controlled by regulatory T cells, we conclude that these T cells are highly restricted in their specificity in that they preferentially see a determinant which also depends upon the aspartic acid in position 100. The data suggest that the VH to D boundary serves as a target of idiotypic selection.