Idiotypic regulation by isologous monoclonal anti-idiotope antibodies

Soluble ACE2 correlates with severe COVID-19 and can impair antibody responses

Identifying immune modulators that impact neutralizing antibody responses against severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is of great relevance. We postulated that high serum concentrations of soluble angiotensin-converting enzyme 2 (sACE2) might mask the spike and interfere with antibody maturation toward the SARS-CoV-2-receptor-binding motif (RBM). We tested 717 longitudinal samples from 295 COVID-19 patients and showed a 2- to 10-fold increase of enzymatically active sACE2 (a-sACE2), with up to 1 μg/mL total sACE2 in moderate and severe patients. Fifty percent of COVID-19 sera inhibited ACE2 activity, in contrast to 1.3% of healthy donors and 4% of non-COVID-19 pneumonia patients. A mild inverse correlation of a-sACE2 with RBM-directed serum antibodies was observed. In silico, we show that sACE2 concentrations measured in COVID-19 sera can disrupt germinal center formation and inhibit timely production of high-affinity antibodies. We suggest that sACE2 is a biomarker for COVID-19 and that soluble receptors may contribute to immune suppression informing vaccine design.

A design strategy to generate a SARS-CoV-2 RBD vaccine that abrogates ACE2 binding and improves neutralizing antibody responses

The structure-based design of antigens holds promise for developing vaccines with higher efficacy and improved safety profiles. We postulate that abrogation of host receptor interaction bears potential for the improvement of vaccines by preventing antigen-induced modification of receptor function as well as the displacement or masking of the immunogen. Antigen modifications may yet destroy epitopes crucial for antibody neutralization. Here, we present a methodology that integrates deep mutational scans to identify and score SARS-CoV-2 receptor binding domain variants that maintain immunogenicity, but lack interaction with the widely expressed host receptor. Single point mutations were scored in silico, validated in vitro, and applied in vivo. Our top-scoring variant receptor binding domain-G502E prevented spike-induced cell-to-cell fusion, receptor internalization, and improved neutralizing antibody responses by 3.3-fold in rabbit immunizations. We name our strategy BIBAX for body-inert, B-cell-activating vaccines, which in the future may be applied beyond SARS-CoV-2 for the improvement of vaccines by design.

The transfer of immunity from mother to child

The newborn's immune system grows fast from a small size at birth by exposure primarily to the intestinal microflora normally obtained from the mother at and after birth. While building up its immune system, the infant is supported by the transplacental IgG antibodies, which also contain anti-idiotypic antibodies, possibly also actively priming the offspring. The second mode of transfer of immunity occurs via the milk. Numerous major protective components, including secretory IgA (SIgA) antibodies and lactoferrin, are present. The breastfed infant is better protected against numerous common infections than the non-breastfed. Breastfeeding also seems to actively stimulate the infant's immune system by anti-idiotypes, uptake of milk lymphocytes, cytokines, etc. Therefore, the breastfed child continues to be better protected against various infections for some years. Vaccine responses are also often enhanced in breastfed infants. Long-lasting protection against certain immunological diseases such as allergies and celiac disease is also noted.

Somatic transgene immunization with DNA encoding an immunoglobulin heavy chain

A plasmid DNA containing a chimeric immunoglobulin heavy-chain gene with tissue-specific promoter and enhancer elements was used as a model system to study the events triggered by a single intraspleen DNA inoculation in adult C57Bl/6 mice. A single intraspleen inoculation was followed in a week by secretion of transgene immunoglobulins and production of immunoglobulin M (IgM) anti-immunoglobulins. Their kinetics of serum appearance were almost superimposable. While anti-immunoglobulin antibodies remained detectable for over 6 months, transgene immunoglobulins disappeared after 3-4 weeks. However, transgene mRNA was detected in the spleen for 4 months. A multiplex polymerase chain reaction (PCR) analysis on splenic genomic DNA 17 days after inoculation demonstrated that the transgene was integrated in the host chromosomal DNA. The nucleotide sequence of the rearranged VDJ region from splenic genomic DNA was identical to that of the parental plasmid DNA, hence ruling out that hypermutation had occurred. A booster injection of immunoglobulin encoded by the transgene on day 200 elicited a typical secondary immune response with IgG1 and IgG2b antibodies. These results demonstrate that a single inoculation of an immunoglobulin heavy-chain DNA targeted to spleen lymphocytes leads to spontaneous integration of the transgene into the host DNA, and that this is sufficient to initiate immunity and establish immunologic memory. Our data also show that minute amounts (<100 ng/ml) of an endogenously produced protein secreted in the microenvironment of a lymphoid tissue generate immunity and establish immunologic memory rather than tolerance.

Treatment with dsDNA-anti-dsDNA antibody complexes extends survival, decreases anti-dsDNA antibody production and reduces severity of nephritis in MRLlpr mice

Lupus nephritis results from the deposition on the glomerular basement membrane of antibodies cross-reacting with dsDNA. In an attempt to suppress the production of such antibodies in the MRLlpr mouse strain, mice were treated by injections of dsDNA-anti-dsDNA antibody complexes formed in an excess of syngeneic polyclonal antibodies to increase the immunogenicity of idiotypes. A first group of mice was treated after the onset of high-affinity anti-dsDNA IgG antibodies (3 months). We show here that fortnightly injections of dsDNA-anti-dsDNA antibody complexes significantly extend mouse survival over that of two control groups treated with either the carrier buffer or with sham complexes. Treated mice produced 5-fold less anti-dsDNA antibodies than control mice and presented a reduced nephritis activity index at the age of 7 months. Specific anti-idiotypic antibody levels were not modified in the treated group, while showing a sharp decrease in the control group between months 6 and 7. Mice of a second group were started on injections of dsDNA-anti-dsDNA complexes at the age of 4 months when nephritis was already ongoing, and were followed until death while receiving fortnightly injections. Forty percent of the treated mice were still alive after one year, while none of the control mice survived. dsDNA-anti-dsDNA complexes have therefore the potential of reducing the production of anti-dsDNA antibody production and the severity of nephritis in MRLlpr mice. These findings could be relevant for the treatment of human lupus.

Correlation between immune maturation and idiotypic network recognition

The maturation of T-dependent humoral immune responses is mediated by somatic mutations. Antigen selection is one mechanism for the activation of B cell clones which express antibodies with progressively increased affinity and which are derived as somatic variants from germ-line-encoded genes. However, the emergence of B cell clones secreting rather low-affinity antibodies and the shift to alternative germ-line V region gene combinations during secondary and tertiary responses cannot be explained by antigen selection. It has been considered that idiotypic suppression may favor this clonal shift. Such an involvement would require that idiotypic recognition in the syngeneic host must be highly restricted to private idiotopes of each clone sequentially activated during immune maturation. To test this possibility, we produced 19 syngeneic anti-idiotypic antibodies to the germ-line-encoded major Ox1 idiotype (IgM-IdOx1 H11.5) of the anti-2-phenyl-oxazolone (phOx) immune response in BALB/c mice. The fine specificity of these anti-IdOx1 was tested with a set of anti-phOx monoclonal antibodies, representing the first steps of maturation. About half of the anti-IdOx1 showed almost no reactivity with the IdOx1 after the switch to IgG and none of the anti-IdOx1 reacted with anti-phOx antibodies which carried a glycine or histidine instead of arginine as the middle amino acid of the D region. These observations suggest a strong correlation between immune maturation and the idiotypic network. A model is presented in which idiotypic suppression may function as a driving force for diversification and maturation of the antigen-induced immune response.

Allergen-sensitive atopic dermatitis is improved by injections of allergen combined with F(ab')2 fragments of specific antibodies

Symptoms of atopic dermatitis (AD) can be provoked by exposure to airborne allergens. We have previously shown that patients hypersensitive to D. pteronyssinus (Dpt) allergens were improved by administration of complexes composed of specific antibodies and allergen, which reduce the allergen-specific immune response. We now report that similar results can be achieved by using F(ab')2 fragments of specific antibodies instead of whole antibody molecules. Eight adult patients with severe AD were included in a single-blind study. During the first 11 months patients were maintained on injections of carrier buffer alone, in an effort to evaluate the extent of spontaneous improvement. They were then treated with intradermal injections of allergen-F(ab')2 complexes made from autologous specific antibodies and Dpt allergens. The majority of the patients improved spontaneously during the summer months, with an average 30% reduction of symptoms. However, a much more pronounced improvement was observed after 3 months on active therapy, corresponding to a cumulative amount of 60 micrograms F(ab')2 and 15 micrograms allergens. The patients continued to improve over the next 5 months, showing an average 83% reduction of severity scores. The use of F(ab')2 antibody fragments reduces the risk of inducing an anti-allotypic immune response, and raises the possibility of adding adjuvants to allergen-antibody complexes and/or using specific antibodies isolated from pooled gammaglobulins.

Maternal immunization modulates the primary immune response to 2-phenyl-oxazolone in BALB/c mice

The development of the antibody repertoire in newborn mice is greatly influenced by idiotype network interactions. It has been demonstrated that anti-idiotypic antibodies either directly injected or transferred from the mother may alter the repertoire for life. For an elucidation of the underlying mechanisms we have analyzed the primary immune response to 2-phenyl-5-oxazolone (phOx) coupled to chicken serum albumin (CSA) in BALB/c mice after complete disappearance of maternal antibodies which originated from different stages of affinity maturation. Depending on the serum titers of the mothers after primary (1 degree mo), secondary (2 degrees mo) or tertiary (3 degrees mo) immunization, maternal anti-phOx IgG persisted in F1 mice for up to 9 months. In addition, F1 mice born to 2 degrees mo developed--even without immunization--an anti-phOx IgM titer which reached levels similar to an antigen-induced primary response. An enhancement of the early primary anti-phOx as well as anti-CSA response was seen in F1 mice born from 1 degree mo, whereas the response was delayed when born to 2 degrees mo and 3 degrees mo. The antibody titers in the latter group of mice remained at a lower level for 3 months. In contrast, mice of the F2 generation which received a smaller amount of the same collection of maternal antibodies as F1 mice from 3 degrees mo exhibited a quite different primary response: (i) They showed an earlier onset in their anti-CSA response. (ii) Whereas normally a plateau in antibody titer was reached by the 4th weak after immunization, in 55% of the F2 mice a prolonged increase of the anti-phOx and anti-CSA antibody titers was observed. At 12 weeks after antigenic challenge, titers reached plateau levels of 6 x 10(5) which were never before seen in a primary phOx or CSA response. Thus, depending on its own immunological experience, the maternal immune system induces a state of memory in the offspring which results in a faster and/or enhanced immune response in the F1 and F2 [corrected] generations.

Immune responses of young mice to pneumococcal type 9V polysaccharide-tetanus toxoid conjugate

Pneumococcal type 9V polysaccharide (PS), contained in the current pneumococcal vaccine, induces only a weak antibody response in young children and therefore is not an effective vaccine for young children. To increase its immunogenicity, a conjugate of PS to a protein carrier, tetanus toxoid (TT), was prepared. To quantify the immune response, mouse anti-9V PS immunoglobulin G (IgG) and IgM reference standards were established. Young mice immunized at 2 weeks of age produced IgM antibody in response to 9V PS alone or 9V PS conjugated to TT. However, only the 9V PS-TT conjugate induced an IgG antibody response and an anamnestic effect. Thus, a covalent linkage between TT and 9V PS was required for isotype switching from IgM to IgG. 9V PS-TT adsorbed with aluminum hydroxide adjuvant resulted in a fivefold or greater increase in the IgG antibody level. We also studied the effect of maternal immunization on the immune response of young mice to 9V PS-TT. Maternal immunization before mating or before mating and during gestation primed 2-week-old progeny given two injections of 9V PS-TT to produce more IgM antibody than progeny from unimmunized mothers. The IgG antibody level of neonates at birth was similar to that observed in the mothers and was probably passive antibody. These results indicate that maternal immunization with an optimum dose of a PS-protein conjugate before and/or during pregnancy, followed by immunization of the offspring with the conjugate, could provide young children with an enhanced IgM antibody response to pneumococcal PSs.

Immunoreactivity between a monoclonal lupus autoantibody and the arginine/aspartic acid repeats within the U1-snRNP 70K autoantigen is conformationally restricted

Immunoreactivity of the arginine/aspartic acid (RD) repeats of the 70K protein of U1 small nuclear ribonucleoprotein (snRNP) was determined to be conformationally dependent. The monoclonal autoantibody 2.73, isolated from a lupus-prone MRL/n mouse model, is reactive with the RD repeat regions of U1 snRNP 70K protein. Immunochemical analysis of the antigenic determinants with use of chemically synthesized peptides characterized the 2.73 epitope as the RD repeat [Pelsue, S., et al. (1993) Autoimmunity, 15, 231-236] Analysis by circular dichroism (CD) and nuclear magnetic resonance spectroscopy indicates conformational preferences in the immunoreactive peptides. Computer analyses of CD spectra obtained on the RD-containing peptides predict beta-turns and beta-sheet to be the preferred conformations of the RD repeats. This structure was also predicted by the Chou-Fasman algorithm. The RD repeat is believed to be a conserved structural motif; however, the biological function is still unclear. Immunological and biochemical analysis of autoimmune antibodies and their respective antigenic determinants has helped to characterize the possible mechanisms that lead to autoimmune diseases. This is the first report of a conformationally dependent, linear epitope of an autoantibody.

Injections of complexes made of dsDNA and specific polyclonal antibodies extend MRL lpr mouse survival: a pilot study

Antibodies towards double-strain (ds) DNA are responsible for the development of lupus nephritis both in human and animal models. A method by which one would suppress the production of pathogenic idiotypes could therefore prevent the development of nephritis. To this end, we prepared polyclonal anti-dsDNA antibodies by immunoaffinity from a serum pool of MRL/MpJ-lpr mice, a strain that develops an early form of nephritis identical to its human counterpart. Antigen-antibody complexes were prepared by addition of dsDNA. Such complexes have the potential of altering the anti-DNA antibody response and boosting the production of specific anti-idiotypic antibodies. Two groups of 14 MRL lpr mice were treated by regular intraperitoneal injections of 10 micrograms dsDNA-anti-dsDNA complexes or carrier buffer, starting at the age of 4 weeks, namely, prior to the appearance of nephritogenic anti-dsDNA IgG antibodies. We show here that such a treatment significantly extended the survival of treated mice compared with the control group. Five treated mice were still alive at month 11 compared with two in the control group. In addition, microscopic kidney examination at the time of death showed less lesions in the treated group compared with controls. This study indicates that complexes made of dsDNA and anti-dsDNA can delay the development of nephritis in the MRL lpr mouse strain.

Maternal immunity and antibody response of neonatal mice to pneumococcal type 19F polysaccharide

The effect of immunization of mothers on the antibody response of their young to pneumococcal type 19F polysaccharide was studied. When 2-week-old BALB/c mice from mothers immunized with 23-valent pneumococcal vaccine during gestation were given an additional dose of the same vaccine, mouse pneumococcal antiserum, or both, they produced higher titers of antibodies to the 19F polysaccharide (1.87 to 4.66 micrograms of 19F immunoglobulin M [IgM] antibody per ml of serum; 0.45 to 0.81 micrograms of IgG antibody per ml of serum) than the control group that did not receive any treatment after birth (0.69 micrograms of 19F IgM antibody per ml; 0.28 micrograms of 19F IgG antibody per ml) (P less than 0.01). Furthermore, all 11- to 12-week-old monkeys that received an additional dose of 23-valent vaccine, pneumococcal immunoglobulin, or both produced statistically higher titers of IgG antibody to the 19F polysaccharide than did controls at various ages. The titers (micrograms of IgG antibody per milliliter of serum) were as follows: vaccine group, 7.12 +/- 0.96; control group at 4 months of age, 3.82 +/- 0.74 (P less than 0.01); immunoglobulin-treated group, 6.85 +/- 0.76; vaccinated and immunoglobulin-treated group, 7.80 +/- 1.40; control group at 3 months of age, 3.01 +/- 0.61 (P less than 0.01). These results suggest that immunization of mothers under certain conditions, such as with an optimum dose of antigen at a critical period of gestation or postnatal development, could provide young infants with an enhanced antibody response to pneumococcal polysaccharide immunogens.

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.

Pathogenic anti-DNA antibodies in SLE: idiotypic families and genetic origins

We have adopted an idiotypic approach to study the double stranded DNA (dsDNA) binding antibodies of systemic lupus erythematosus (SLE). Three anti-idiotypic reagents, 8.12, 3I, and F4, identify cross reactive idiotypes that are each expressed on anti-dsDNA antibodies in the sera of many patients with SLE. These idiotypic antibodies are implicated in the pathogenesis of SLE as they are present in immune complex deposits in the kidneys of patients with SLE glomerulonephritis. The autoantibody associated idiotypes are also expressed on antibodies that do not bind DNA. We are investigating the origin of the pathogenic anti-dsDNA antibodies of SLE by comparing the autoantibodies, the antibodies to foreign antigens, and the myeloma proteins that express each SLE associated idiotype. In conjunction with serological analysis of these idiotypic systems, molecular genetic studies indicate that both the 8.12 and the 3I autoantibody associated idiotypes may be germline encoded, while the F4 idiotype is generated by somatic mutation. The data further suggest that the antigenic specificity of the pathogenic anti-DNA antibodies of SLE is acquired through somatic mutation of germline immunoglobulin genes. By studying the regulation of genes capable of encoding pathogenic autoantibodies, in both SLE patients and non-autoimmune individuals, we may be able to elucidate the pathogenesis of autoimmune disease and begin to design more effective therapeutic interventions.

Induction of antigen-specific immunity with monoclonal anti-idiotypic antibodies in vivo: differences in potency and comparison of immunochemical properties

Anti-idiotypic (Id) antibodies provide a means other than antigen of clone-specific regulation of immune responses, and have been proposed as an alternative form of vaccine. However, the requirements for effective induction of immunity by anti-Id are not understood. Nine monoclonal anti-idiotope antibodies (anti-Id mAb) were derived in the Ia. 7 model system. While all nine anti-Id mAb induced comparable Ab3 responses in vivo as detected by ELISA, there were dramatic differences in the potency of the antigen-specific components of the responses induced by the nine anti-Id mAb. Anti-Id mAb that were indistinguishable in isotype, combining site relatedness, fine specificity on a panel of mAb, end point binding titers, competitive binding and ability to induce Ab3 differed dramatically in their ability to induce antigen-specific immunity in vivo, thus ruling out several models for explaining differences in induction.

Human immunoglobulin G and immunoglobulin G subclasses: biochemical, genetic, and clinical aspects

Human IgG consists of two identical heavy (H) chains and two identical light (L) chains joined by interchain disulfide bridges. Heterogeneity in the amino acid sequences of the H and L polypeptides results in at least three types of IgG variants at the structural and genetic levels. The four isotypic forms are IgG1, IgG2, IgG3, and IgG4, which share extensive homologies in the primary structure of their H chains. As a result, the subclasses cross-react antigenically, but they can be differentiated on the basis of subtle architectural dissimilarities. The biological and effector properties of the IgG isotypes have been associated, in part, with their structural differences. Genes determining the synthesis of human IgG heavy chains are located on chromosome 14. In several clinical situations the isotypes appear to be regulated or expressed in patterns reflecting the gene arrangement. The numeric designations of the subclasses correspond to the order of their proportional amounts in healthy adult serum: IgG1 greater than IgG2 greater than IgG3 greater than IgG4. Awareness of the importance of the roles of the four IgG isotypes in human health has steadily increased since they were first described in the 1960s. The recognition that deficits or increases in selected IgG subclasses may have clinical consequences has prompted considerable interest in quantifying the four isotypes in clinical specimens. In particular, deficiencies of IgG2, IgG3, and IgG4, singly or combined, are associated with chronic infections which may not be readily recognized in otherwise healthy people with normal serum total IgG concentrations. Different assay methods using polyclonal or monoclonal antisera with various calibrants have been applied; however, no standardized method exists at the present. IgG deficits are associated with gene defects and are acquired in secondary immunodeficiencies in conjunction with other disorders. IgG isotype selectivity has been recognized in autoimmune diseases and in response to carbohydrate and protein antigens derived from pathogenic microorganisms and common allergens.

Xenogeneic antibodies and atopic disease

Xenogeneic antibodies can survive food processing procedures with their biological activity intact and even enhanced. These antibodies can be absorbed from the human gut, and will function both as antigens and antibodies in the human immune system. Antibodies to bovine gamma globulins (BGG) have been detected in human sera and the family of anti-BGG antibodies must include anti-idiotypic antibodies, very low doses of which can influence the immune response. The hypothesis is that the human immune system may be primed by low-level exposure to xenogeneic antibodies specific for those human allergens which are ubiquitous in the farm environment, such as pollens, mites, and moulds, the result being a deleterious and inappropriate response on subsequent exposure to these allergens. Dairy products are the most important source of xenogeneic antibodies in the western diet, and the hypothesis may partly explain the association between cow's milk and allergies to substances other than milk proteins.

Perturbation of the autoimmune network. I. Immunization with anti-idiotypic antibodies prior to challenge with antigen induces quantitative variations in the autoantibody response

The effect of immunization with anti-idiotypes on the production of autoantibodies subsequently induced with nominal antigen, thyroglobulin, was investigated in BALB/c mice with three distinct rabbit antibodies and one syngeneic monoclonal antibody (mAb) specific for an idiotype (Id62) borne on a mouse monoclonal autoantibody to thyroglobulin. In these in vivo experiments, dose, route and form of the anti-idiotypic immunization were kept constant, but the time interval between exposure to anti-idiotype and antigen challenge was varied. When the interval was short (two weeks), heterologous anti-Id62 antibodies predisposed to suppression of the autoantibody response in 2/3 instances. Suppression was also obtained in mice immunized with a syngeneic mAb directed against Id62. In each case, a prominent idiotype-positive (Id') response was measured in the serum. Adsorption/elution studies indicated that Id' molecules in suppressed mice were principally non antigen-binding. On the other hand, when the time interval between injections was long (14 weeks), mice preimmunized with one rabbit anti-Id62 antibody showed a markedly increased autoantibody response. The Id' component in enhanced mice was largely enriched for antibodies reacting with the antigen. These findings suggest that the state of activation of autoreactive clones and the type of anti-idiotypes used may be determinant factors in the overall effect of manipulation of autoimmune responses with anti-idiotypic 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.

Tumor-specific idiotopes on suppressor factors and suppressor cells revealed by monoclonal anti-idiotope antibodies

Two monoclonal anti-idiotope antibodies, previously found to induce tumor-specific cell-mediated immunity in mice, were examined for their relationship to tumor-associated suppressor factors (SF), produced in culture by spleen cells from tumor-bearing mice or present in sera from such mice. A leukocyte adherence inhibition assay was used to detect cellular immunoreactivity to tumor antigens and its inhibition by SF, using peritoneal cells from mice bearing tumor or sensitized with anti-idiotope antibody. The SF were specifically absorbed by the corresponding anti-idiotope antibodies coupled to a solid phase and were recovered by elution. They were also specifically neutralized by the addition of the respective antibodies to the assay system. Anti-idiotope antibody, used with complement to pretreat spleen cells from tumor-bearing mice, prevented these cells from producing SF in culture. Tumor antigen-reactive effector cells, suppressor cells, and SF thus share similar idiotopes, permitting their respective functions to be modulated by appropriate anti-idiotopes.

Regulation of the immune response. II. Concomitant idiotope-specific enhancement and suppression can result in a phenotypically normal response

Idiotope-specific immunoenhancement or suppression was induced in C57BL/6 mice by the injection of physiological amounts (100 ng-10 micrograms) of monoclonal anti-idiotope antibody. As previously described, nanogram doses enhanced idiotope expression while a 10-micrograms dose of anti-idiotope antibody induced the activation of a population of Thy 1.2+, Lyt 1-, 2+ suppressors. Both positive and negative regulatory activities were confined to the non-mu, idiotope+ compartment of the plaque-forming cell response. Administration of intermediate doses of anti-idiotope antibody resulted in an immune state indistinguishable from that of naive mice. This apparently normal response was in fact the product of a simultaneous activation of balanced enhancing and suppressive activities. When treated with anti-Lyt 2 or Lyt 1 and complement, spleen cell populations taken from such phenotypically "naive" mice revealed latent idiotope-specific immunoenhancement or suppression, demonstrating the components of a functional regulatory equilibrium.

Immunoresponses to Neisseria meningitidis epitopes: suppression of secondary response to phosphorylcholine is carrier specific

Results of our previous work have shown that Neisseria meningitidis serogroup B M986 can induce a phosphorylcholine (PC)-specific plaque-forming cell immunoresponse in mice. Also, a single injection of a relatively low dose of meningococci in NBF1 female mice induced a priming time-dependent suppression on subsequent meningococcus challenge. This suppression was not due to switching to another class of immunoglobulin nor to the presence of a capsule on N. meningitidis. In this study we show that suppression induced by meningococcus is carrier specific. Furthermore, we offer evidence suggesting that the structure(s) on meningococcus that trigger this suppression is heat labile and different from the antigenic structure(s) recognized by the suppressed B cells. In addition, we found that there is a gradual increase in antibody secretion rates of N. meningitidis-induced anti-PC plaque-forming cells that correlates with N. meningitidis priming time. Rather unexpected was the fact that pretreatment of mice with PC-keyhole limpet hemocyanin (thymus-dependent antigen) had a great influence on the subsequent PC-specific immunoresponses induced by N. meningitidis and PC-coupled heat-inactivated meningococcus [PC-(NMB)HI], as shown by (i) a striking decrease in T15 idiotype expression, (ii) concomitant direct anti-PC plaque-forming cells reduction, (iii) switching to immunoglobulin G (N. meningitidis-induced immunoresponse) or immunoglobulin G plus immunoglobulin A [PC-(NMB)HI-induced immunoresponse], and (iv) a significant increase in heterogeneity of plaque-forming cell secretion rates. The possibility that N. meningitidis, PC-(NMB)HI, and PC-KLH stimulate B lymphocytes pertaining to three different subpopulations embedded in distinct regulatory circuits is discussed, with emphasis on the interrelationships between T-dependent and T-independent lymphocyte compartments. We focus on the possibility of the existence of high-level regulatory circuits in which lymphocyte subpopulations or sets of lymphocyte subpopulations with different requirements of activation are connected.

RISH V. Application to monoclonal antibody production

RISH considers that cell surface components involved in like cell identification are not involved in the structure of the plasma membrane per se and are attached to a part of their mRNA. The mRNA then acts as a template for the synthesis of DNA. Thus the component at the cell surface is attached to an RNA/DNA receptor. If there is a conformational change in the component (antigen) this will cause a distortion in its RNA/DNA receptor. This distortion is then detected by a tissue specific T lymphocyte which removes all or part of the RNA/DNA receptor from the aberrant cell and the lymphocyte then undergoes replication. During this process receptor RNA/DNA is incorporated into the daughter lymphocyte which becomes a B lymphocyte/plasma cell producing immunoglobulin. The initial tissue specific T lymphocyte becomes a dual functional helper/suppressor cell. The plasma cell after the initial immune response becomes a circulating memory B cell displaying IgM or IgD. If this cell complexes an antigen with its surface IgM or IgD a humoral immune response will be developed as previously described, but in this case the antibodies produced will be anti-idiotypic antibodies. The anti-idiotypic antibodies will regulate the production of the antibody directed against the antigen per se. The anti-idiotypic antibodies will in turn be regulated by a second anti-idiotypic antibody. In RISH five such anti-idiotypic systems may be involved in regulating the immune response to the initial non-immunoglobulin antigen. Based on the RISH anti-idiotypic mechanism a system is briefly described whereby human memory B cells, to a particular antigen, may be isolated. These B cells may then be activated to secrete immunoglobulin with autologous isolated anti-idiotypic antibodies. These activated cells may then be infected with E.B. virus to establish an immortal cell line of B cells secreting the immunoglobulin of interest.

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.

Analysis of nondominant idiotypes expressed during alloimmune responses

The antibody response of Lewis rats (RT1.A) to class I MHC antigens of the Brown Norway rat (RT1.An) was studied. Diversity of the serum alloimmune response was analyzed using syngeneic anti-idiotype raised against monoclonal antibodies of the same specificity. Cross-reactive idiotypes were detected on approximately one in one thousand Lewis anti-RT1.An serum antibodies, at concentrations ranging from 20 to 600 ng/ml. The kinetics of idiotype expression coincided with that of total anti-BN antibody production, suggesting that both were regulated by the same mechanism. To determine whether humoral anti-idiotype was involved in such regulation, sera from these animals were screened for anti-idiotype content. Using an RIA sensitive to 20 ng/ml, no humoral anti-idiotype could be detected during any phase of the alloimmune response.

Specificity of antibody and helper T-cell responses to the isologous myeloma protein W3129 and its subunits

The specificity of BALB/c antibodies and Th elicited by BALB/c myeloma protein W3129 (alpha, kappa) and its subunits was studied. Antibodies were detected with RIA and ELISA techniques. Th were demonstrated by their ability to augment a secondary anti-NIP antibody response in a Mitchison type assay of adoptive immunity. The major proportion of antibodies elicited by the complete W3129 was directed to an idiotypic determinant(s) that depended on assembled H + L chains. The determinant(s) was probably located in or near the antibody combining site because binding was hapten-inhibitable. A second minor antibody population bound an idiotypic determinant(s) on VW3129H expressed on isolated H-chain as well as on the complete myeloma protein. A third and very weakly reactive set of antibodies was specific for a C alpha antigenic site(s) which was expressed much more efficiently on free than on assembled alpha-chains. The antibody response to free kappa W3129 was directed to idiotypic determinants that were inaccessible in the complete molecule. By contrast, free kappa W3129 elicited Th that responded to an idiotypic determinant(s) on VW3129K; the determinant(s) was expressed on both the isolated chain and the complete W3129, suggesting that Th responded to an idiotope not recognized by B-cells. Priming with free alpha W3129 failed in four out of five experiments to induce Th that responded to the complete W3129, demonstrating that a major difference existed between VH and VL of W3129 regarding their immunogenicity for Th. Nevertheless, free alpha W3129 did elicit antibody responses that displayed high reactivity with the complete molecule, indicating that certain serologically defined antigenic sites on the surface of W3129 are also expressed on isolated alpha W3129. Thus, certain differences were detected as to the specificities of Th and B-cells for W3129 and its subunits since they recognized separate idiotopes located in the VL- or VH-region, respectively. The pattern of Th recognition of W3129 resembled that of another isologous myeloma protein, M315, but was unlike that of a third, J558, previously described from this laboratory.

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

Monoclonal antibodies detecting idiotopes on the germ line-encoded anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibody B1-8 were injected at various doses into newborn mice and the expression of B1-8 idiotopes was measured in anti-NP responses in later life. Suppression was long lasting, and a 100-fold increase in the dose of anti-idiotope delayed recovery from suppression by 5-6 weeks. Upon injection of a single anti-idiotope, suppression was observed for all B1-8 idiotopes to various degrees. Certain idiotopically defined antibody phenotypes were much more efficiently suppressed, and later recovered from suppression, than others. This specificity pattern was observed at the level of both B and T cells from the manipulated animals, as demonstrated in cell transfer experiments in which such cells were mixed with normal T and B cells. In these experiments, there was evidence for suppression mediated by regulatory T (and possibly also B) cells. Whereas the B cells from the manipulated animals were idiotypically unresponsive in a T cell-dependent adoptive primary response, the frequency of lipopolysaccharide-reactive B cells expressing the target idiotype was only slightly reduced in these animals as compared to control mice. Together with data on the elimination of anti-idiotope antibody from the neonatally injected animals these results are interpreted in the following way: idiotype suppression is induced through the reaction of anti-idiotope with idiotopes expressed on the surface of newly generated B cells, at microgram concentrations of anti-idiotope. When the concentration of anti-idiotope fall below that level, recovery from suppression sets in. Two types of suppression are induced. The first, namely, direct blockade of B cell maturation, is short-lived. The second involves the induction of regulatory cells, perhaps through idiotope-bearing antibody V regions complexed by anti-idiotope. This type of suppression is long-lived and its specificity depends upon the distribution of the target idiotope in the antibody repertoire and/or peculiarities of the T cell receptor repertoire. It impinges on the selection of the B cell repertoire in the animal as expressed in T cell-dependent (and possibly other) responses and is thus hardly seen at the level of lipopolysaccharide-reactive (immature) cells. Idiotype suppression by regulatory cells may be perpetuated by antigen interacting with idiotypic antibodies on the B cell surface and may therefore play a role in establishing tolerance not only for the expressed antibody repertoire, but for self antigens in general.

Mechanism of neonatally induced idiotype suppression and its relevance for the acquisition of self-tolerance

We present an analysis of the elimination of a monoclonal anti-idiotope antibody injected into C57BL/6 mice on the day of birth. During the first 4 weeks of life the antibody is eliminated from the circulation with a slow half-life, ranging from 15-18 days. This finding makes sense biologically as the animals depend at that time on maternally transmitted antibodies. After 4 weeks elimination speeds up considerably. The rate of elimination appears to be the same for a 1 microgram and a 100 microgram dose. The elimination data and previous results on the specificity, duration and cellular basis of idiotype suppression induced by the monoclonal anti-idiotope fit into the following model of idiotype suppression, which is in good accord with other experimental evidence on idiotype and allotype suppression in the literature: suppression depends strictly on the concentration of anti-idiotope in the cellular environment. As long as it is in the microgram range, the generation of idiotope-bearing B cells from pre-B cells is prevented. The system recovers quickly from this type of suppression, as soon as the concentration of anti-idiotope falls below that range. A second type of suppression is also induced in the anti-idiotope-treated animals. It is long-lived (8-10 weeks longer that the first type), has a peculiar specificity in that it affects, in our particular case, only a certain subset of the antibodies bearing the target idiotope, and involves regulatory T (and possibly B) cells which prevent the functional maturation of B cells expressing those antibodies in the animal. Suppression of this type also depends strictly on anti-idiotope concentration and is induced either at the time when the generation of idiotope-bearing B cells from pre-B cells is still inhibited or just thereafter, when such cells begin to appear in the system and the anti-idiotope concentration is still at a few hundred nanograms per ml. Experimental evidence indicates that in the induction of suppression, the primary target of the anti-idiotope are idiotope-bearing antibodies variable regions. We assume that those variable regions, complexed by anti-idiotope are the inducers of regulatory (suppressive) T cells. Idiotype suppression may also be induced upon interaction of antibody variable regions (and possibly other receptors) with ligands other than anti-idiotypic antibodies. We, therefore, think that idiotype suppression not only establishes self-tolerance within the antibody system, but is a mechanism of self-tolerance in general.

An unusual suppression of immune response: pretreatment with Poly(Glu60,Phe40) suppresses response to poly(Glu60,Phe40)

The synthetic random copolymer poly( Glu60 , Phe40 ) ( GPhe ) is an excellent immunogen in SWR/J (H-2q) mice. The intravenous injection of soluble GPhe by itself led to antibody production and GPhe -specific T-lymphocyte proliferation. The proliferating lymphocyte was sensitive to anti-Thy 1.2 and anti-Ly 1 antisera. A subsequent immunization with GPhe should therefore lead to an enhanced response. Yet, a single intravenous injection of an aqueous solution of GPhe suppressed the immune response to a subsequent immunization with GPhe in CFA as measured by GPhe -specific plaque-forming colonies, ELISA, T-cell proliferation, and delayed-type hyper-sensitivity. The suppression was not transferable from pretreated mice into normal or irradiated syngeneic recipients with either sera or lymphoid cells. The antibody generated from the pretreatment could not be responsible for the suppression as injection of SWR anti- GPhe antibody into SWR/J mice enhanced, rather than suppressed, the response to the subsequent immunization with GPhe . Pretreatment of mice with a rabbit anti-idiotypic antiserum produced against (SWR anti- GPhe antisera) had no effect on the immune response to GPhe . Thus, the suppression cannot be explained by a simple B-cell tolerance mechanism. This type of unusual suppression was observed only with mice of H-2q haplotype and not with mice of H-2 haplotypes a and k which are also responders to GPhe .

Idiotope regulation by isotype switch variants of two monoclonal antiidiotope antibodies

Previous work has shown that the injection of antiidiotope antibodies specific for idiotopes of the germline-encoded anti-(4-hydroxy-3-nitro-phenyl) acetyl (NP) antibody B1-8 enhanced or suppressed the expression of B1-8 idiotopes in subsequent humoral anti-NP responses, depending on the dose and perhaps also the isotype of the injected antibody. To formally answer the question of whether the isotype of an antiidiotope determines its effector function in this type of idiotypic control, we have performed regulatory experiments with isotype switch variants selected from two hybridomas secreting anti-B1-8 idiotopes of CBA (Ighj) and C57BL/6 (Ighb) origin. The antibodies of each variant family differ from each other only in the constant region of the heavy chain. The results show that, irrespective of whether an antiidiotope antibody belongs to the IgG1, IgG2b, IgG2a, or IgE class, a 10-ng dose enhances idiotope expression whereas a dose of 10 micrograms exerts a suppressive effect. It emerges from the present and parallel data that the expression of antibody V regions resembling idiotypically that of antibody B1-8 can be enhanced and suppressed by any of four antiidiotope antibodies that recognize distinct idiotopes on those V regions. This suggests that the initial step in the regulatory process induced by an antiidiotope is its binding to antibody V regions carrying the target idiotope. The antiidiotopes preferentially regulate the expression of antibodies that coexpress with the target idiotope other B1-8 idiotopes, despite the fact that some B1-8 idiotopes are also expressed independently of each other in anti-NP responses of idiotypically unmanipulated mice. This finding may reflect high affinity binding of the antiidiotopes to the target against which they were originally raised (i.e., antibody B1-8) or, more likely, a preferential recognition of B1-8-like V regions by regulatory T cells.

Fc-dependent effector functions of idiotype-anti-idiotype immune complexes

Some effector functions of antigen-antibody and antibody-antibody (idiotype-anti-idiotype) complexes were analyzed. As a model system a monoclonal IgM antibody specific for the hapten NP (antibody B1-8) was reacted either with hapten and hapten-carrier conjugates or with monoclonal anti-idiotope antibodies with specificity for B1-8 idiotopes. The precipitating, C1q-binding, complement-activating and Fc receptor binding properties of these complexes were compared. Binding of both hapten-carrier conjugates and anti-idiotope antibodies to B1-8 results in formation of complexes which depending on the B1-8:ligand ratio precipitate, activate complement, bind C1q and exhibit increased avidity for Fc mu and Fc gamma receptors of mouse spleen cells. In both types of complexes cross-linking of IgM molecules is essential for triggering these Fc-dependent functions, and a functional heterogeneity if idiotype-anti-idiotope complexes based on different idiotype-anti-idiotope ratios could also be observed. The functional similarity of B1-8-hapten-carrier and B1-8-anti-idiotope complexes suggests that regulatory functions so far assigned to antigen-antibody complexes could be carried out also by idiotype-anti-idiotope complexes.

Allotypic restriction of the expression of MOPC460 idiotope after immunization with either anti-2,4-dinitrophenyl (DNP) or anti-idiotypic antibodies

The MOPC460 idiotype is expressed in mice with the IghCa allotypic haplotype after anti-2,4-dinitrophenyl (DNP) immunization. We have previously shown that two monoclonal syngeneic anti-idiotypic antibodies (IDM 92-13 and IDM 41-27) define two distinct idiotopes (the 460.92 and the 460.41) on the M460 idiotype. The current study demonstrates that only one idiotope (460.92) is recurrently expressed after antigen immunization in IghCa positive mice and also that, immunization against the monoclonal anti-idiotypic molecules induces the synthesis of 460.92 idiotope positive anti-DNP antibodies. However, the detection of such molecules is only possible when animals with the IghCa allotypic haplotype are immunized with the IDM 92-13 molecules. Immunization of mice with either of the two monoclonal anti-idiotypic antibodies never results in the synthesis 460.41 positive molecules. Therefore, whatever protocol of immunization used, the expression of 460.92 was allotypic restricted.

Rapid and sensitive procedure for assigning idiotypic determinants to heavy or light chains: application to idiotopes associated with the major cross-reactive idiotype of A/J anti-phenylarsonate antibodies

A rapid and sensitive procedure is described for assigning idiotypic determinants to heavy or light polypeptide chains. Heavy and light chains are resolved by electrophoresis in the presence of sodium dodecyl sulfate. The electrophoretically resolved polypeptides are then transferred to nitrocellulose filters. Filters containing bound heavy and light chains are incubated with 125I-labelled anti-idiotypic antibody, and idiotype-anti-idiotype reactivity visualized by autoradiography. This procedure is illustrated with three monoclonal anti-idiotopic antibodies which recognize determinants associated with the major cross-reactive idiotype family of A/J anti-phenylarsonate antibodies. All three anti-idiotopic antibodies are shown to react with electrophoretically resolved idiotype heavy chain, but not with idiotype light chain.

ABPC 48 cross-reactive idiotopes in BALB/c mice. Natural and levan-induced expression

Using monoclonal antiidiotypic antibodies, we developed a sensitive binding assay that detects molecules with one or with two idiotopes of the ABPC48 idiotype. ABPC48 cross-reactive idiotypes were thus shown to be present in substantial amounts in sera of nonimmunized mice. Levan binding sites are found on these idiotypes. During the life time of the mice, the natural anti-levan titer increases while ABPC48 idiotypic expression remains constant, suggesting different controls for these two activities. On the other hand, ABPC48 cross-reactive idiotypes participate--as minor components--in the response that follows a deliberate immunization with bacterial levan. This induction process is likely to reflect the selection of idiotopes expressed by the B cell clones preactivated in sera of nonimmunized mice rather than the activation of silent clones. We suggest that a similar situation might explain the reported emergence of ABPC48 idiotypes in animals primed with antiidiotypic antibodies and subsequently stimulated with levan.

Anti-idiotypes against anti-H-2 antibodies VI. Detection of shared idiotypes among monoclonal anti-H-2 antibodies

Anti-idiotypes produced against monoclonal anti-H-2 antibodies have been used to examine idiotope sharing among a panel of anti-major histocompatibility complex (MHC) antibodies detecting the same and different specificities. Both xenogeneic anti-100-30 and anti-3-83, which did not react with predominant idiotypes in conventional alloantisera, detected idiotopes on 3-83 and 100-30 as well as on 2 other monoclonal anti-H-2Kk antibodies. All 4 monoclonal antibodies recognized the same epitope cluster on the Kk molecule and detected the same serological specificity. H-2.5. In contrast, syngeneic and allogeneic anti-idiotype produced against the same monoclonal antibodies did not detect these cross-reactive determinants. In several instances, xenogeneic anti-idiotype reacted with anti-MHC antibodies which recognized distinct H-2 determinants, suggesting that anti-MHC antibodies detecting the same or different specificities may share idiotypic determinants. These reagents may be useful probes of the anti-MHC immune repertoire.

Analysis of the repertoire of anti-idiotypic B-cell responses to self-I-Ak- or -I-Ek-reactive monoclonal antibodies in A.TL mice

Twenty anti-idiotypic antisera (anti-Ids) were produced in A.TL mice to self-I-Ak or -I-Ek-reactive monoclonal antibodies (mAbs), constructed in the A.TH anti-A.TL combination. The reactivity of these anti-Ids was examined in a panel of 31 anti-Iak A.TH mAbs, using direct idiotype binding, cross-competitive inhibition of idiotype binding, and isoelectrofocusing (IEF) assays. Among 13 anti-Ids produced against anti-I-Ak mAbs, one only recognized individual idiotypic specificities (IdIs) on its corresponding mAb, while the 12 others identified homologous IdIs and recurrent idiotypic specificities also expressed on heterologous anti-I-Ak and/or I-Ek mAbs. Two sets of major cross-reactive idiotypes (IdXs) were characterized on two groups of mAbs recognizing public Ia.1, I-Ak,f,u and r) or private (Ia.2, I-Ak) determinants clustered in two spatially distinct epitope regions of the I-Ak molecule, respectively. By contrast, most (5/7) of the anti-Ids raised against mAbs recognizing polymorphic or monomorphic (Ia.7-like) I-Ek determinants displayed specificity apparently restricted to their corresponding mAb IdIs. This finding contrasted with the previous characterization, using xenogeneic anti-idiotypic reagents, of an interstrain IdX expressed on all mAbs defining Ia.7-like determinants in the IEk epitope group I. These data indicate that A.TL mice can readily develop anti-idiotypic responses towards self Ia-reactive mAb minor idiotypes (IdIs) and that recognition of anti-Iak mAb IdXs in such mice is preferentially observed when anti-I-Ak mAbs are used as immunogens.