Requirements for prolonged suppression of an idiotypic specificity in adult mice

Fc-signalling in the modulation of immune responses by passive antibody

Passive antibody can both suppress and augment immune responses. Until recently, there was virtual unanimity on the importance of the interaction of the Fc portion of modulating antibody with Fc-receptors (Fc-signalling), especially in experiments involving the suppression by antibody. Experiments reported in the last few years, that do not demonstrate the range of Fc-portion/Fc-receptor influences on the suppression of immune responses by passive antibody, have introduced new uncertainty into this field. The purpose of this paper is to review how the initial controversy on the influence of Fc-signalling in inhibition by passive antibody was resolved. Old and new approaches are suggested that may help in resolving the current uncertainty engendered by recent experimental results that were interpreted to mean that passive suppressive antibody does not utilize the inhibitory FcgammaRIIB receptor. An understanding of the factors that influence negative Fc-signalling is needed in order to optimize clinical therapies whose action depends on the suppressive property of antibody.

Regulatory influences of neonatal multispecific antibodies on the developing B cell repertoire

In these studies we have emphasized the apparent developmental hierarchy of B cell development and assigned a role for the multispecific self idiotype reactive B cells which develop first, in promoting the development of later appearing clones of B cells. These early sets of interconnecting clones of B cells bridge between clones of cells involved in such disparate responses as anti-PC and anti-DEX. Interference with these idiotype directed interactions results in deficiencies in the adult B cell repertoire with respect to these responses. These idiotype directed interactions appear to be bidirectional in that interference with either antigen, Ab1, Ab2, Ab3, and Ab4 during neonatal life all produce striking effects on the adult responses to these antigens. These results strongly suggest that early idiotype directed interactions between B cells are essential for the establishment of the adult B cell repertoire.

Prevention of experimental autoimmune uveoretinitis by active immunization with autoantigen-specific monoclonal antibodies

Preimmunization of Lewis rats with anti-S antigen (S-Ag) monoclonal antibodies (mAb) led to protection against experimental autoimmune uveoretinitis (EAU) induced by this retinal autoantigen. High titers of anti-idiotypic (anti-Id) antibodies were raised against three mouse mAb, S2D2 (IgG2b), S6H8 (IgG2a) and S7D6 (IgG1), directed at S-Ag. An almost complete prevention was observed in S2D2 mAb-immunized animals while a partial protection was achieved with S6H8 and S7D6 mAb. No detectable anti-Id antibody nor disease prevention was observed in rats immunized with the mAb S9E2 (IgG2a) which only recognizes bovine and sheep S-Ag, or with control mAb of the same isotypes irrelevant to S-Ag. The mAb treatment did not modify the level of the whole polyclonal antibody response to S-Ag. These results suggest an important role in the pathogenesis of EAU for the epitopes recognized by S2D2-S6H8 and S7D6 in the S-Ag molecule. The success of anti-Id immunization for autoimmune disease suppression may depend on the identification of relevant epitopes.

Enhancement and suppression of an intrastrain cross-reactive idiotype

The effects of a copolymer of monoclonal anti-idiotype (7B7.10) with keyhole limpet haemocyanin (KLH), designated 7-K, on an ongoing immune response were investigated. It was found that the response could be diverted to the production of higher titres of anti-p-azobenzenearsonate (Ar) antibodies, of which nearly 100% carry an intrastrain cross-reactive idiotype (CRIA). The effect was observed only in mice that had received a pre-inoculation of KLH-Ar, or KLH plus bovine gamma globulin-Ar (BGG-Ar). The effect was also observed, however, when cross-linked 7B7.10 was mixed, rather than conjugated with KLH, suggesting that the role of KLH was to induce the production of a B-cell growth factor. Cross-linked 7B7.10 was not effective in the absence of KLH. A primary inoculation of 7-K together with KLH-Ar did not result in significant suppression or enhancement of CRIA. Also, pre-inoculation of 7-K alone did not suppress a subsequent idiotypic response to KLH-Ar, whereas monomeric anti-Id was suppressive. This supports a possible role for the unmodified Fc segment in the suppressive mechanism. In mice primed with KLH-Ar, before administration of 7-K, CRI+A molecules lacking anti-Ar activity were present in very low concentrations in the immune sera. Larger quantities of such molecules were present in the sera of mice that received 7-K alone. The methods described permit the reproducible production of large amounts of CRI+A anti-Ar antibodies.

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.

Effect of syngeneic anti-idiotypic antibody on influenza virus neuraminidase antibody response

Influenza viruses possess two major surface glycoproteins - hemagglutinin (HA) and neuraminidase (NA). Py203, a monoclonal antibody (Ab) specific for the neuraminidase of the PR8 (H1N1) influenza virus, was used to prepare syngeneic monoclonal anti-idiotypic (anti-Id) Abs. From a BALB/c mouse immunized with Py203 (anti-N1), we obtained RM1, a monoclonal anti-Id Ab. The Py203-Id was detected in a significant fraction of immunoglobulins (Igs) in the primary and secondary responses elicited by PR8 (H1N1) and X31 (H3N2) viruses. In animals injected with minute amounts of RM1 and subsequently boosted with an identical dose of RM1, no detectable anti-NA activity was noted, but a significant increase in Py203-Id-bearing Igs was observed. In the sera of animals injected with minute amounts of RM1 and subsequently boosted with PR8 (H1N1) or X31 (H3N2) viruses, an increase in anti-NA activity and in the level of Py203-Id was noted. Animals injected with large amounts of RM1 and boosted with PR8 and X31 showed a marked suppression of the Py203-Id but no alteration in the anti-NA response. The anti-Id recognizes an idiotope (the Py203 idiotope) shared by antibodies specific for the N1 and N2 neuraminidase variants.

Idiotype-directed interactions during ontogeny play a major role in the establishment of the adult B cell repertoire

IgM hybridomas derived from perinatal B cells show a high degree of auto-reactivity and many had demonstrable anti-idiotypic reactivities by binding studies. Selected multispecific antibodies were also shown to have potent idiotype-specific biological activities and if administered at appropriate stages of development could dramatically alter the responses of these mice when challenged with appropriate antigens in adult life. The results obtained suggest that idiotype-directed interactions between neonatal B cells play an important role in the early establishment of the B cell repertoire which is subsequently expressed in adult mice.

Lymphocyte activation by the Fc region of immunoglobulins

The Fc region of Ig is required for numerous biological effector functions which include: opsonization, anaphylaxis, C fixation, catabolism of the Ig molecule, FcR binding, and immune regulation. To this latter point, the cellular and subcellular events involved in immune regulation by IC and Fc fragments of Ig have been the focus of numerous investigations. Characterization of cyanogen bromide cleavage fragments from a human IgG1 myeloma protein indicates that one biologically-active site is found in residues 335-357 of the CH3 domain of the molecule. Synthesis of the biologically-active region resulted in a peptide, termed p23, which stimulates mouse and human B cells to secrete polyclonal Ig and activates AA metabolic pathways. In contrast to these findings, p23 is unable to induce B cell proliferation or IL-1 secretion from macrophages. Analysis of data obtained with overlapping peptides, based on p23, suggests that the minimal active sequence needed for B cell differentiation is leu-pro-pro-ser-arg (residues 351-355). In contrast, only p23 or p23 minus the carboxyterminal glu356 and glu357 were able to induce PGE release. Release of biologically-active peptides derived from the Fc region of Ig into the cellular microenvironment may form the nucleus of a nonspecific in vivo immunoregulatory network. The specificity of peptide regulatory activities could reside in their effectiveness at high concentrations in the cellular microenvironment. The interaction of Fc region peptides with receptors on B cells, T cells, and macrophages/monocytes could result in a dynamic control of immune reactivity.

Quantitative measurements of an intrastrain cross-reactive idiotype in IgE antibodies

This paper describes the development of methods for quantitation of an intrastrain cross-reactive idiotype (CRIA) in IgE antibodies directed to the p-azophenylarsonate (Ar) group and their application to normally immunized and idiotypically suppressed mice. The data were validated by the use of monoclonal and serum anti-Ar antibodies known to possess or lack CRIA. The idiotype was absent in the IgE as well as the total anti-Ar population of idiotypically suppressed mice. A good correlation was noted between the CRIA content of total and IgE anti-Ar with a trend toward a somewhat lower content in the IgE population. Irradiated mice that received immune cells prior to further immunization expressed relatively low concentrations of the idiotype (per weight unit of anti-Ar). The method will be useful in studies of the regulation of the switch to IgE synthesis.

Antiidiotype modulation of herpes simplex virus infection leading to increased pathogenicity

Antiidiotype reagents that recognize idiotypic determinants associated with the combining site of monoclonal antibodies to herpes simplex virus type 2 ( HSV2 ) were used to manipulate the immune response to HSV2 in BALB/c mice. The injection of antiidiotype antibodies into mice before challenge with a 50% lethal dose of HSV2 resulted in a shorter survival time than that of mice receiving either preimmune rabbit immunoglobulin G or antiidiotype reagents against hepatitis B surface antigen before HSV2 challenge. These findings indicate that the immune response to HSV2 in mice can be modulated through idiotype- antiidiotype networks, thereby increasing the pathogenicity of HSV2 infections.

Enhancement of the immune response to hepatitis B surface antigen. In vivo administration of antiidiotype induces anti-HBs that expresses a similar idiotype

BALB/c mice receiving antiidiotype antibodies before the injection of hepatitis B surface antigen (HBsAg) generated an enhanced anti-HBs response. Mice given antiidiotype antibodies in a soluble form induced predominantly IgM anti-HBs, whereas alum-precipitated antiidiotype produced primarily IgG anti-HBs. Injection of antiidiotype antibodies alone induced anti-HBs that inhibited a common interspecies anti-HBs idiotype-antiidiotype reaction and recognized the group-specific determinant of HBsAg. These data support the view that antiidiotype antibodies may modulate the immune response to an infectious viral agent.

Suppression of in vitro monoclonal human rheumatoid factor synthesis by antiidiotypic antibody. Target cells and molecular requirements

Previous studies have indicated that antiidiotypic antibody can modulate expression of idiotype both in vivo and in vitro. Although the precise mechanisms underlying modulation of idiotype expression by antiidiotype remains unclear, a requirement for intact IgG antiidiotypic antibody has been suggested and T cells appear to play a role in some systems. We have studied peripheral blood mononuclear leukocytes (MNL) from a patient with a B cell lymphoma and a circulating IgMK rheumatoid factor (RF) paraprotein in an effort to delineate mechanisms involved in regulation of idiotype expression by antiidiotypic antibody. 1-10% of MNL from this patient could be cytoplasmically stained with specific F(ab')2 antiidiotypic antibody. MNL from the patient spontaneously synthesized IgM RF in culture that possessed the same idiotype as the circulating IgM RF paraprotein. Production of RF by MNL was suppressed by pretreatment with either intact IgG or the F(ab')2 fragments of antiidiotypic antibody (50% inhibitory concentration was 0.2 and 1.1 micrograms/culture, respectively). In contrast, the Fab' fragment of antiidiotypic antibody was not inhibitory (up to 57 micrograms/culture) despite retaining demonstrable antiidiotype activity. Suppression of RF production was not observed over the same concentration range with the IgG or F(ab')2 fractions of a non-cross-reactive antiidiotypic antibody prepared against another monoclonal IgMK RF paraprotein or with IgG or F(ab')2 fractions prepared from normal rabbit serum. Inhibition of RF production by antiidiotypic antibody did not require T cells. Antiidiotypic antibody decreased intracellular and extracellular levels of idiotype indicating diminished synthesis of idiotype by the patient's B cells. Synthesis of IgM RF by MNL obtained from unrelated donors was not suppressed by the antiidiotypic antibody specific for the patient's paraprotein. The results indicate that (a) antiidiotypic antibody is capable of directly suppressing human B cell release of idiotype, (b) the bivalent antigen-binding fragment (F[ab']2) of antiidiotypic antibody is sufficient for mediating such suppression, (c) an intact Fc portion of antiidiotypic antibody enhances suppression of idiotype, and (d) antiidiotypic antibody inhibits idiotype expression by suppressing synthesis of idiotype.

T and B cells that recognize the same antigen do not transcribe similar heavy chain variable region gene segments

We have attempted to determine whether T cells and B cells that have the same antigenic specificity and whose receptors share idiotypic determinants in fact express similar VH gene segments. To do this, we have obtained and characterized a cDNA clone containing the entire coding sequence for the VH gene from a glutamic acid60/alanine30/tyrosine10 (GAT)-binding immunoglobulin that carries the CGAT idiotype. The GAT-VH clone was hybridized to Northern blots of GAT-specific T cell RNAs; there was no evidence of a T cell transcript that hybridized to the GAT-VH probe. The T cells analyzed included: (a) 10 GAT-binding suppressor T cell hybridomas, 6 of which secreted factors with CGAT idiotypic determinants, (b) one GAT-specific helper T cell hybridoma, and (c) two GAT-specific helper T cell lines grown in the absence of feeder cells. The detection limit of the Northern blot analysis was 1-2 copies of a particular mRNA species per cell for the hybridomas and 5-10 copies per cell for the T cell lines. Therefore, we conclude that T and B lymphocytes responding to GAT do not utilize similar VH gene segments. Furthermore, the presence of idiotypic determinants on T lymphocytes does not necessarily imply close structural similarity between T and B cell antigen receptors.

Anti-idiotype antibody-dependent cell-mediated cytotoxicity (ADCC) against idiotype-bearing cells

The present report demonstrates that cells expressing idiotypic determinants on their surfaces can be specifically destroyed by anti-idiotypic antibodies acting as inducers of antibody-dependent cell-mediated cytotoxicity. Lysis of surface-idiotype-positive hybridoma cells was effected by mouse spleen cells, mouse peritoneal cells, or human blood mononuclear cells, in the presence of anti-idiotypic antibodies. In order for lysis to occur, the simultaneous presence of Fc receptor-bearing cytotoxic cells and anti-idiotypic antibodies was required. Specificity of lysis was conferred by the anti-idiotypic antibody. Hybridoma cells expressing a different idiotype could not be lysed. Anti-idiotypic antibody-dependent cell-mediated cytotoxicity against 51Cr-labeled cells expressing a particular idiotype could be induced by the specific anti-idiotypic antibodies and inhibited by unlabeled idiotype-positive cells or by idiotype in a soluble form. Cytotoxicity could not be inhibited by the presence of bystander cells or monoclonal antibodies expressing a different idiotype. It is proposed that ADCC lysis of idiotype-positive cells has important implications for understanding the regulation of immune responses by an idiotype-anti-idiotype network. This cytolytic pathway provides an extremely specific and effective mode of control of idiotype-positive cells by anti-idiotype antibody. Previous observations that an intact Fc fragment was necessary for anti-idiotype antibodies to exert suppressive effects in vivo further support this hypothesis.

Idiotype connectance in the immune system. I. Expression of a cross-reactive idiotype on induced anti-p-azophenylarsonate antibodies and on endogenous antibodies not specific for arsonate

A new cross-reactive idiotope family (CRIAD8) is described that contains subpopulations of antibodies binding to different epitopes. One subpopulation occurs naturally in normal sera from strain A mice, is found mainly on IgG2 and IgG3 subclasses, does not bind p-azobenzenearsonate (ABA)+, does not express CRI5Ci, and can be selectively stimulated by low doses of antiidiotype antibody (AD8). The second subpopulation is not found in normal serum, binds ABA, is found on all IgG subclasses, expresses CRI5Ci, and is selectively stimulated by ABA-conjugated proteins. Since CRIAD8 was found on both subpopulations of antibody, and since each subpopulation could be selectively expanded, it was possible to study the effect that expansion of the ABA- CRIAD8+ set had on subsequent responses elicited by ABA-keyhole limpet hemocyanin (KLH) in the ABA+ CRIAD8+ set. In these experiments, prior immunization with AD8 restricted the subsequent response of the ABA+ CRIAD8+ set to ABA-KLH. Furthermore, only those doses of AD8 that stimulated the ABA-CRIAD8+ set reduced the responsiveness of the ABA+ CRIAD8+ set to ABA-KLH, suggesting that the two phenomena are causally related. These findings argue that CRIAD8 correlates well with a regulatory idiotope and that immune responses by lymphocyte clones that have different antigen-binding specificities can affect one another as a result of their sharing such an idiotope. These results strongly favor a network organization of the immune system.

Passive transfer of the idiotypically suppressed state by serum from suppressed mice and transfer of suppression from mothers to offspring

Mice that are suppressed with respect to an idiotype (CRIA) present in A/J anti-p-azophenylarsonate antibodies, hyperimmunized, and allowed to rest were previously found to possess high concentrations of suppressor T cells with anti-idiotypic receptors. We have now observed that the sera of such mice contain soluble factors that can selectively suppress the CRIA component of a humoral response when passively transferred to adult or neonatal recipients. When T cells from suppressed, hyperimmunized mice were transferred into female mice before mating, their offspring, upon immunization, produced anti-Ar antibodies that lacked CRIA. A state of idiotypic suppression was also produced in offspring when the mother was inoculated with serum from suppressed mice a few days before parturition. The results indicate that the suppressor factor is not an immunoglobulin.

Structural analysis of monoclonal anti-arsonate antibodies: idiotypic specificities are determined by the heavy chain

Hybrid immunoglobulin molecules were constructed from the isolated heavy and light chains of monoclonal anti-arsonate antibodies which differed in their expression of a cross-reactive idiotype. The reconstructed molecules were tested for public and private idiotypic determinants associated with the A-strain response to the hapten p-azophenylarsonate and it was found that both an appropriate heavy chain and an appropriate light chain were required for expression of idiotypic determinants. While appropriate heavy chains could be derived only from idiotype-positive antibodies, appropriate light chains could be derived not only from idiotype positive antibodies, but also from certain idiotype-negative molecules. Similarly, recombinant (hybrid) molecules constructed from two idiotype-positive immunoglobulins differing quantitatively in the degree of idiotypic character, expressed the character at a level which correlated with that of the heavy chain donor. Thus, while the serological expression of idiotypic determinants occurs only in the context of the appropriate VHVL combination, these data demonstrate that the determinants comprising the major cross-reactive idiotype of the anti-arsonate response of A/J mice have their bases in heavy chain structures.

Anti-idiotypic immunity and autoimmunity. I. In vitro and in vivo effects of anti-idiotypic antibodies to spontaneously occurring autoantibodies to rat thyroglobulin

The effects of anti-receptor (anti-idiotypic) immunity on autoimmune responses have been investigated in Buffalo (BUF) rats with autoimmune thyroiditis. As compared to other animal models of autoimmune disease, BUF rat thyroiditis has the following advantages: it occurs in an inbred strain, arises spontaneously (i.e. without the experimental administration of autoantigens and adjuvants) and is characterized by production of autoantibodies to only one autoantigen, thyroglobulin. Finally, its pathogenesis is mediated by autoantibodies to rat thyroglobulin, and therefore this model is particularly suitable to study the effects of anti-idiotypic reactions on those autoimmune disorders whose damage is caused by humoral immunity. The experiments reported in the present study show that first, heterologous anti-idiotypic antibodies to autoantibodies against rat thyroglobulin have been produced and characterized. It has then been demonstrated that such anti-idiotypic antibodies are capable of inhibiting the in vitro binding between thyroglobulin and thyroglobulin autoantibodies obtained from BUF rats. It has also been shown that repeated injections of anti-idiotypic antibodies into sublethally X-irradiated BUF rats with autoimmune thyroiditis were followed by a significant change in the levels of circulating autoantibodies to rat thyroglobulin. These results provide evidence that in spite of the complexity of autoantigens and the heterogeneity of autoimmune responses, established autoimmune diseases may be controlled by sequential immunosuppression and anti-idiotypic immunity.

Autoregulation of immune responses via idiotype network interactions

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Polyclonal activation of Ts cells with antiserum directed against an IGH-1 linked candidate for a T-cell receptor constant region marker

An anti-T cell serum raised in allotype congenic mice recognizes the product of a new locus coding for a heavy chain-linked polypeptide found on a subpopulation of T cells. Anti-Tsd raised in BALB/cAnN mice against selected C.AL-20 T cells reacts with a cell surface antigen in virgin animals that is found on 25% of mature thymocytes and Lyt-bearing T cells, but not on prothymocytes, Lyt1 T cells or B cells. The antigen is restricted to strains bearing the Ig-1d and Ig-1e heavy chain allotype haplotypes, and is expressed in the F1 animal. The antigen is unlinked in expression to the Lyt2, H-2, or kappa light chain loci. The antigen is not detected in the hematopoietic cells in the bone marrow and appears to mark only the mature peripheral pool of T cells. As previously reported, the antiserum blocks the binding of suppressor T cells to the cross-reactive idiotype for arsonate, while reagents specific for Fab, Fc and Ig were ineffective. It seems probable that the marker may represent a T cell constant region marker analogous to the Igh products on immunoglobulin. Antiserum against this marker induces in vivo triggering of Ts cells for a wide variety of T-dependent antigens. All subclasses of anti-hapten antibodies are suppressed; no affinity restrictions or clonotype specificity is observed in suppressed adult mice. Results suggest that precursor T cells regulating major serum idiotypes regulate individual idiotypes.

A mature T lymphocyte subpopulation marker closely linked to the Ig-1 allotype Ch locus

An antiserum raised in BALB/c AnN mice against selected CAL.20 T cells reacts with a cell surface antigen in virgin animals that is found on 25% of mature thymocytes and Lyt-2-bearing T cells, but not on prothymocytes, Lyt-1 T cells or B cells. The antigen is restricted to strains carrying the Ig-1d or Ig-1e heavy chain allotype haplotypes. It is expressed in F1 mice. The antiserum blocks the binding of suppressor T cells to the cross-reacting idiotype for arsonate while reagents specific for Fab, Fc or Ig were ineffective. We suggest that the antigen described represents a determinant on the product of a new locus coding for a heavy chain-linked polypeptide found on a subpopulation of T cells.

Antigen- and receptor-driven regulatory mechanisms. I. Induction of suppressor T cells with anti-idiotypic antibodies

Delayed-type hypersensitivity (DTH) to the azobenzenearsonate (ABA) hapten can be readily induced in A/J mice injecting ABA-coupled syngeneic spleen cells subcutaneously. To further characterize this T-cell-dependent immunological phenomenon, the effect of passively administered anti-cross-reactive idiotype common to anti-ABA antibodies of A/J mice (CRI) antibodies on the development of ABA-specific DTH was investigated. Animals given daily injections (of minute amounts) of anti-CRI antibodies subsequent to immunization with ABA-coupled cells show significant reduction of ABA specific responses. This inhibition is antigen specific and requires the intact immunoglobulin molecule, as F(ab')2 treatments were ineffective in suppressing the reaction. Investigations of the mechanism of the anti-CRI-induced suppression of ABA DTH revealed that the observed suppression is a result of the activation of suppressor cells. Spleen cells taken from animals which received anti-CRI antibodies were able to adoptively transfer suppression to naive recipients. This suppression was shown to be mediated by T cells, as anti-Thy1.2 plus complement completely abrogated the transfer of suppression. In addition, animals pretreated with low doses of cyclophosphamide were not suppressed by the administration of anti-CRI antibodies. The genetic restriction of anti-CRI-induced suppression was demonstrated. Antibodies to the major cross-reactive idiotype, (CRI) associated with anti-ABA antibodies in A/J mice were unable to suppress the development of DTH to ABA in BALB/c mice (H-2d, Igh-1a). Such antibodies were, however, fully active in suppressing ABA DTH in the allotype-congenic C.AL-20 strain which has an allotype (Igh-1d) similar to that of A/J (Igh-1e) on a BALB/c background, and which produces humoral antibodies with the CRI.

Effect of idiotype-specific suppressor T cells on primary and secondary responses

Previous reports have shown that suppression of idiotype can be adoptively transferred by T cells, or by rosettes containing T cells with anti-idiotypic receptors, from an idiotypically suppressed, syngeneic mouse. The present data indicate that secondary B cells are highly resistant to such suppression. Priming recipients to the relevant hapten, p-azophenylarsonate, 6 days or 4 mo before the adoptive transfer prevented suppression. This was independent of the carrier used for the hapten group during priming or subsequent immunization, suggesting that resistance to suppression is attributable to secondary cells with specificity for the hapten. The effect of suppressor T cells could also be overcome by mixing them with specifically purified B cells having receptors for the hapten group before the adoptive transfer. Adoptive transfer of the suppressed state by specifically purified B cells from suppressed, hyperimmunized animals confirmed our previous finding that the suppression of idiotype can also be caused by B cells lacking idiotypic receptors, evidently through a mechanism involving clonal dominance. Possible mechanisms of idiotypic suppression by T cells are discussed.

Complete inhibition of the expression of an idiotype by a mechanism of B-cell dominance

Mice of the C.AL-20 strain, which express genes controlling CH regions of the AL/N strain on a BALB/c background, normally synthesize antibodies to the p-azophenylarsonate group (anti-Ar antibodies) with an idiotype characteristic of the A strain. The synthesis of the idiotype, as quantitated by a sensitive assay, can be completely inhibited by the transfer of leukocytes from BALB/c mice producing anti-Ar antibodies, which lack the idiotype. A number of control experiments show that the inhibition is not attributable to suppressor T cells and that the synergistic action of such cells is not required. The results indicate that B-cell dominance, mediated by secondary cells, can completely prevent the expression of unprimed cells with receptors of the same specificity. It is uncertain whether this effect is due entirely to selective capture of antigen by the secondary cells, or whether some type of active suppression by B cells is involved.

Antibody-specific immunoregulation

In recent years, much evidence has accumulated which demonstrates that an animal's immune system has the capacity to recognize its own antibody idiotypes. These findings suggest that self-idiotypic recognition may potentially play a role in the regulation of B-cell responses. The experiments presented in this report were carried out to determine if an animal develops the ability to specifically regulate the synthesis of antibodies specific for an antigen, subsequent to primary immunization to the particular antigen and concomitant with an initial antibody response. Employing the splenic fragment culture system we have compared the response of primary donor B cells in irradiated recipients which have been previously immunized to hemocyanin (Hy) alone or dinitrophenyl (DNP)-Hy plus Hy. The results indicated that only 25-30 percent of DNP- specific B cells stimulated by DNP-Hy in Hy immunized recipients could bestimulated by DNP-Hy in recipients immunized with Hy as well as DNP-Hy. B-cell responses to other haptens, such as fluoresceinated-Hy, and secondary DNP-specific B-cell responses were unaffected in DNP-Hy immunized animals. The nontrivial and specific nature of the observed decrease in primary DNP-specific B-cell responses was verified by the finding that the response of CB20 donor cells, which differ from BALB/c mice only in the immunoglobulin heavy chain allotype-linked locus, was unaffected in BALB/c recipient mice which had been immunized with DNP-Hy. Thus, it appeared that during a primary humoral immune response to a T- dependent antigen, an antibody-specific regulatory mechanism is induced which specifically limits the stimulation of hapten-specific primary, but not secondary, B cells. The important implications that these findings have for the understanding of the control of primary B-cell responses and the generation of secondary B cells is discussed.

Presence on idiotype-specific suppressor T cells of receptors that interact with molecules bearing the idiotype

All A/J mice produce anti-p-azophenylarsonate (anti-Ar) antibodies, some of which share a cross-reactive idiotype. The idiotype can be suppressed by treatment with anti-idiotypic antiserum before immunization, although normal concentrations of anti-Ar antibodies are synthesized. We have previously reported that such suppressed mice, if hyperimmunized and then allowed to rest, contain up to 10% of splenic T cells which form rosettes with autologous RBC coated with Fab fragments of anti-Ar antibodies bearing the idiotype. Our present results indicate that the rosette-forming T cells include the idiotype-specific suppressor T-cell population. The suppressive activity is largely depleted by removal of the rosette-forming lymphocytes, and the rosettes themselves are highly suppressive. The data do not establish whether all of the idiotype-specific rosette-forming cells are suppressor cells. The system may provide a source of large numbers of suppressor cells for further study, and facilitate investigation of the mechanism of generation of idiotype-specific suppressor cells.

Transfer of idiotype suppression and idiotypes by leukocytes from ascitic fluids

A procedure is described for producing ascites containing both high concentrations of antibodies and immunologically active leukocytes. In mice that were immunologically suppressed with respect to a cross-reactive idiotype, the ascitic cells were found to be very active in adoptively transferring the suppressed state to mildly irradiated, syngeneic recipients and simultaneously transferring the capacity to produce the "private" idiotype characteristic of the donor's anti-p-azophenylarsonate antibodies. The participation of both T and B cells is therefore suggested. As few as 2 x 10(6) cells were sufficient for suppression and for inducing the production of the private idiotype in the recipient, in concentrations comparable to that of the donor mouse. A single donor can thus be used to colonize many recipients with the private idiotype, without sacrifice of the donor. The method should be useful in structural studies of antibodies of a given specificity with different idiotypes, and for investigations of the mechanism of idiotype suppression, as well as other studies in cellular immunology.

Binding to idiotypic determinants of large proportions of thymus-derived lymphocytes in idiotypically suppressed mice

All A/J mice immunized with a conjugate of p-azophenylarsonate groups to keyhole limpet hemocyanin produce antibodies against azophenylarsonate, some of which share a crossreactive idiotype. The appearance of the idiotype can be suppressed, without reducing the response against azophenylarsonate, by injecting rabbit anti-idiotypic antibodies prior to immunization. We have now observed that mice suppressed in this way, or by adoptive transfer of leukocytes from other suppressed mice, and then immunized with the hemocyanin-azophenylarsonate conjugate, possess high proportions (up to 14%) of lymphocytes that form rosettes with A/J erythrocytes coated with Fab fragments possessing the idiotype. Idiotypic specificity was demonstrated by various experiments. Most of all of the rosette-forming lymphocytes appear to be thymus-derived lymphocytes (T cells). Treatment of T cells with trypsin eliminated the capacity to form rosettes, which was restored on standing overnight in medium. Thus, the receptors are synthesized by the cells and are not passively adsorbed. Treatment of mice with anti-idiotypic antiserum without antigenic stimulation did not elicit substantial numbers of rosette-forming cells. The requirement for antigen suggests that antigen-idiotype complexes may be a stimulatory agent. A prolonged rest period after immunization of suppressed mice was required for the induction of high percentages of rosette-forming cells. Rosette formation provides a convenient method for studying factors that induce the formation of idiotype-specific T cells.

Frequency of occurrence of idiotypes associated with anti-p-azophenylarsonate antibodies arising in mice immunologically suppressed with respect to a cross-reactive idiotype

Inoculation of rabbit anti-idiotypic (anti-id) antibodies suppresses the subsequent appearance of a cross-reactive idiotype (CRI) associated with the anti-p-azophenylarsonate (anti-Ar) antibodies of A/J mice. Such suppressed mice produce normal concentrations of anti-Ar antibodies which lack the CRI, but against which anti-id antisera can be prepared. The anti-Ar antibodies of an individual, suppressed mouse do not in general share idiotype with anti-Ar antibodies of other A/J mice, either suppressed or nonsuppressed. The present experiments were undertaken to quantitate several "private idiotypes" in a large number of hyperimmunized A/J mice. Anti-Ar antibodies of three mice, suppressed for the CRI, were labeled with 125I and subjected to isoelectric focusing. Four single peaks, that were over 90% reactive with autologous antiid, were randomly selected for use as ligands in a radioimmunoassay, and ascitic fluids containing anti-Ar antibodies from 181 A/J mice were tested as inhibitors. Two of the four idiotypes could not be detected in any mouse other than the donor. The concentration of the idiotype was less than 1 part in 1,250 to less than 1 part in 25,000 of the anti-Ar antibody population; these are minimum values. A third idiotype was detected in 3 of the 181 mice, but at very low concentrations. The fourth idiotype was present in 28% of the mice, again at a low concentration. The data support the existence of a very large repertoire of anti-Ar antibodies in the A/J strain and are consistent with a process of random somatic mutation for generating diversity in hypervariable regions. It is proposed that the cross-reactive idiotype may be controlled by a germ line gene or a gene related to a germ line gene through a small number of somatic mutations; and that the idiotypes that were not detectable in other mice were the products of genes that had undergone extensive mutations, with a low probability of recurrence in other mice.

A theory of regulation and self-nonself discrimination in an immune network

A mechanism is suggested for the regulation of the immune response that involves antigen-binding and anti-idiotypic lymphocytes. The cross-linking of receptors is postulated to be a general mechanism for triggering T cells, B cells and cytotoxic effector cells (e.g. macrophages). A key role in regulation is ascribed to antigen-specific T cell-dependent factors, which are assumed to be able to block the receptors of both T cells and B cells of the anti-idiotypic specificities. The simple postulates of the model lead to feasible mechanisms for the helper, suppressor and killer roles of T cells, cellular and humoral immune responses, low zone tolerance and the tolerogenic effects of monomers, immune memory, antigenic competition, the abrogation of tolerance with cross-reacting antigens, the usefulness of the switch from IgM to IgG, and self-tolerance to both serum antigens and cell surface antigens. Biological roles are suggested for one of the Ia antigens and beta 2-microglobulin. The theory leads to a number of predictions, which can be tested experimentally. A simple mathematical model is included, which provides an indication of how the theory may be further developed on a quantitative basis.