The expression of a set of antibody variable regions in lipopolysaccharide-reactive B cells at various stages of ontogeny and its control by anti-idiotypic antibody

Membrane IgE Binds and Activates FcεRI in an Antigen-Independent Manner

Interaction of secretory IgE with FcepsilonRI is the prerequisite for allergen-driven cellular responses, fundamental events in immediate and chronic allergic manifestations. Previous studies reported the binding of soluble FcepsilonRIalpha to membrane IgE exposed on B cells. In this study, the functional interaction between human membrane IgE and human FcepsilonRI is presented. Four different IgE versions were expressed in mouse B cell lines, namely: a truncation at the Cepsilon2-Cepsilon3 junction of membrane IgE isoform long, membrane IgE isoform long (without Igalpha/Igbeta BCR accessory proteins), and both epsilonBCRs (containing membrane IgE isoforms short and long). All membrane IgE versions activated a rat basophilic leukemia cell line transfected with human FcepsilonRI, as detected by measuring the release of both preformed and newly synthesized mediators. The interaction led also to Ca(2+) responses in the basophil cell line, while membrane IgE-FcepsilonRI complexes were detected by immunoprecipitation. FcepsilonRI activation by membrane IgE occurs in an Ag-independent manner. Noteworthily, human peripheral blood basophils and monocytes also were activated upon contact with cells bearing membrane IgE. In humans, the presence of FcepsilonRI in several cellular entities suggests a possible membrane IgE-FcepsilonRI-driven cell-cell dialogue, with likely implications for IgE homeostasis in physiology and pathology.

Interrelating B cell subpopulations and environmental regulation with the expression of three tiers of repertoire diversity

The B cell repertoire consists of three tiers of clonotype diversity. One tier, which is the product of H chain V region rearrangements in the absence of N additions, is of limited diversity (less than 10(8) clonotypes) so that clonotypes of this tier would be expected to recur within and among B cells of individuals of an inbred strain. These clonotypes, therefore, could be subjected to, and conserved by, evolutionary selective pressures such as those imposed by ubiquitous bacterial pathogens. The second tier of clonotypes is created by H chain V region rearrangements that include N additions, and is, therefore, exceedingly diverse. Clonotypes of this tier would be unlikely to recur; however, by providing maximal diversity they would ensure protection against a wide spectrum of pathogens. The third tier of diversity is that which is generated by the superimposition of somatic mutations on clonotypes of the other two tiers. This tier of clonotypes is reflective of the refinement of specificities that are destined for expression in memory B cells. B cells exists as three distinct subpopulations, Ly-1 B cells, conventional primary B cells and memory B cells. These subpopulations differ functionally, developmentally, and by the extent to which they are impacted by immunoregulatory processes. Furthermore, B cells of these subpopulations differentially express the three tiers of clonotype diversity.

Comparative expression of adult and fetal V gene repertoires

A hallmark of the immune system is the extraordinary diversity associated with antibodies. This is made possible by a series of genetic rearrangements involving variable region gene segments. Considerable detail is known about these genetic mechanisms except for the enzymatic machinery involved. An important question in studies of the generation of diversity is whether V genes are selected for rearrangement mainly in a random manner or selected by particular developmental rules. Past studies have indicated that the acquisition of fetal and neonatal specificity repertoires is a nonrandom process. In this report, we review our studies that directly compare the adult and fetal/neonatal V gene repertoires. The evidence suggests that the adult repertoire is more diverse with indications of a random use of VH gene families. However, whether V genes are indeed randomly used in the adult remains to be clarified at the VH gene member level. The fetal repertoire, on the other hand, appears nonrandom in V gene usage. In addition, the fetal repertoire is mostly germline encoded with little evidence of junctional diversity. Taken together, the results indicate different rules for generation of the adult and fetal repertoires, findings most likely explain by distinct B cell subsets and B cell progenitors at early stages in ontogeny.

Qualitative difference of anti-DNA antibody-producing cell precursors in the pre-immune B cell repertoire between normal and lupus-prone mice

The precursor frequency for anti-DNA antibody-producing cells in the pre-immune B cell repertoire was investigated in young female BALB/c and NZW mice, and in young and aged female NZB x NZWF1 (B/WF1) mice. Spleen cells from these mice were diluted serially and stimulated polyclonally in vitro with lipopolysaccharide (LPS) and IL-4 to induce both IgM and IgG1 production. The results demonstrated that there existed virtually no difference in precursor frequency for IgM anti-DNA antibody-producing cells between normal and lupus mice, confirming previous observations made by other investigators. In contrast, the number of precursors for IgG1 anti-DNA antibody-producing cells was much higher in young and old B/WF1 mice than in normal mice. These results suggest that the high frequency of precursors for IgG1 anti-DNA antibody-producing cells in the pre-immune B cell repertoire of B/WF1 mice is a crucial factor for the pathogenesis of systemic lupus erythematosus.

Poly(Glu60Ala30Tyr10) (GAT)-induced IgG monoclonal antibodies cross-react with various self and non-self antigens through the complementarity determining regions. Comparison with IgM monoclonal polyreactive natural antibodies

Previous studies have shown that the antibodies of the preimmune repertoire are able to bind to various auto- and xenoantigens including chemical haptens. Sequence analysis of two such murine monoclonal IgM natural autoantibodies showed that they are encoded by unmutated germ-line variable regions of the light and heavy chain (V alpha and VH) genes which were also found in various murine immune responses, like phenyl-oxazolone, dinitrophenyl, arsonate, phosphorylcholine and influenza virus hemagglutinin. These data raised the question as to whether induced antibodies possessing germ-line sequence are also able to react with autoantigens. To study this problem, anti-poly(Glu60Ala30Tyr10) (GAT) and anti-alprenolol (Alp) monoclonal antibodies, carrying similar VH and V alpha genes and the same IgG1 isotype, were examined for their capacity to react with several self and non-self antigens. The results showed that: (a) the anti-GAT antibodies tested reacted with different autoantigens, such as murine tubulin, actin and myosin as well as trinitrophenyl (TNP) and bovine serum albumin. Similarly, one of the anti-Alp showed weak reactivities for myosin, DNA, actin and TNP; (b) in contrast two other anti-Alp antibodies did not react with any of the tested antigens. Since the major differences between the oligoreactive anti-GAT and the monoreactive anti-Alp antibodies are in the complementarity determining regions (CDR) our results suggest that the observed cross-reactions are mediated by hypervariable loops. Sequence comparison of these antibodies indicate a possible correlation between cross-reactivity and the presence of aromatic and charged amino acids in the CDR.

Lack of N regions in fetal and neonatal mouse immunoglobulin V-D-J junctional sequences

Much of T and B lymphocyte receptor diversity derives from the addition of nontemplated N regions at the junctions of receptor gene elements, although fetal T cells expressing gamma/delta receptors lack N regions. I have sequenced immunoglobulin H chain variable regions of PCR-amplified DNA and cDNA from fetal and newborn mouse liver and spleen cells. These sequences showed an absence of N regions. Only 1/87 DNA sequences and 17/146 RNA sequences contained N regions, in striking contrast to adult Ig sequences. These data show that N region insertion is a developmentally regulated process in B cells as well as in T cells, and demonstrate that receptor diversity in neonatal B cells is limited by the absence of N regions as well as by biased usage of Vh genes.

Long-lived B cells: mitogen reactivity as a tool for studying their life-spans

A population of noncycling small lymphocytes has been selectively enriched in mice by treatment with hydroxyurea (HU) over 4 consecutive days. This cell population, present in the spleen of HU-treated mice, contained a high frequency of lipopolysaccharide (LPS)-reactive cells and this could be used as a functional marker to follow their persistence after transfer to LPS-nonresponder recipient mice. The results reported here show that cells selected after a long-term HU treatment have considerably less decay, after transfer in recipient mice, than normal spleen cells. Furthermore, they demonstrate that HU-selected B cells survive in the recipient mice for periods up to 3 months, and are, consequently, true long-lived lymphocytes.

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

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

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

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

Quantitative representation of two germ-line V genes in the early antibody response to 2-phenyloxazolone

Early anti-phenyloxazolone antibodies of BALB/c mice include a subset that bears the nearly or totally unmutated VH-Ox1 sequence. A fraction of this subset also bears the nearly or totally unmutated V kappa-Ox1 sequence. The whole subset is recognized by an anti-idiotype serum 495 and the VH-Ox1/V kappa-Ox1 fraction also by another anti-idiotype serum 260. Frequencies of the VH-Ox1 subset and its V kappa-Ox1 fraction in early IgM and IgG antibodies were determined by typing hybridomas with anti-idiotype antisera. The whole subset appears to make up approximately one half of IgG antibodies, two thirds of this being 495+/260+ in both isotypes. IgM data are less certain but the same frequencies may be valid. Affinities of 495+/260+ antibodies ranged from 1.3 X 10(6) to 11 X 10(6), affinities of 495+/260- antibodies from 0.47 X 10(6) to 1.1 X 10(6), and affinities of doubly negative antibodies were less than 0.41 X 10(6). High affinity is probably an explanation for the high proportion (one third) of the 495+/260+ antibodies in the early response. Doubly negative (and low-affinity) hybridomas may not have been classified as producers of phenyloxazolone antibodies in earlier studies, and this could explain the still higher reported frequency (73%) of VH-Ox1/V kappa-Ox1 antibodies.

Long-lived lymphocytes include lipopolysaccharide-reactive B cells

We have used a new protocol of prolonged in vivo hydroxyurea (HU) administration which eliminates all cycling and short-lived cells. This treatment kills 99% of non-B non-T bone marrow cells, and it leaves in spleen and bone marrow "long-lived" B- and T-cell populations which represent 33 and 59%, respectively, of the total numbers of lymphocytes found in untreated controls. The relative proportions of B and T cells in spleen or blood of HU-treated mice were practically unaffected, while an increased blood-to-marrow permeability results in markedly abnormal proportions of B and T lymphocytes in bone marrow. Mitogen reactivities of these long-lived lymphocytes recovered either in spleen or bone marrow of HU-treated animals were studied. The results show that such B cells respond perfectly well to the B-cell mitogen lipopolysaccharide, by proliferation and differentiation into Ig-secreting cells, and that T cells proliferate at nearly control levels in response to concanavalin A. This protocol of long-term HU treatment offers the possibility of studying selected long-lived lymphocyte populations, the clonal repertoires and functional properties of which can now be readily approached.

Strain-specific silencing of a predominant antidextran clonotype family

The immune response to dextran is characterized by marked phenotypic differences among murine strains. In particular, Igha strains, as opposed to strains of other Igh haplotypes, respond relatively vigorously to dextran B1355 fraction S (DEX), producing predominantly antibodies bearing the lambda light chain, and specific for the alpha(1----3) glucose linkage. We have investigated this disparity in BALB/c (Igha) vs. C.B20 (Ighb) mice at the individual precursor cell level. Consistent with previous findings (7-9, 35, 40, 42, 43), there was a 10-fold higher frequency of lambda-bearing splenic B cells specific for the alpha(1----3) linkage in Igha mice. As with previously studied (25-27) predominant specificities, the origin of this high frequency of lambda-bearing alpha(1----3) DEX-specific B cells appears to be a reflection of a high expression of this specificity in surface Ig (sIg)-negative cells emerging from the bone marrow generative cell pool. Surprisingly, although C.B20 mice (Ighb) have a low frequency of lambda-bearing alpha(1----3) DEX-specific B cells in their mature primary splenic population, the frequency of precursor cells of this clonotype in their sIg- bone marrow cell population is equivalent to that of BALB/c sIg- cells. These cells could only be stimulated in allotype allogeneic (Igha), as opposed to allotype syngeneic (Ighb), carrier-primed irradiated recipients. This finding was confirmed by the finding that a high proportion of antidextran hybridoma cell lines derived from C.B20 bone marrow cells produced lambda-bearing alpha(1----3) DEX-specific antibodies that were IdX+. These findings have led us to conclude that the well-established phenotypic difference between Igha and Ighb mice with respect to the expression of lambda-bearing alpha(1----3) DEX-specific antibody responses is not, as previously assumed, the result of an inability of Ighb mice to generate B cells of this clonotype, but rather, is the product of environmental, possibly antiidiotypic, silencing of cells of this clonotype as they mature in Ighb mice.

Early B cell precursors in long-term bone marrow culture: selective development in the bone marrow of irradiated recipients

The primary site for the growth and differentiation of B cell precursors in irradiated recipient mice was investigated. Bone marrow (BM) cells from lipopolysaccharide (LPS)-responder C57BL/6 mice were transferred into irradiated LPS-nonresponder C57BL/10ScCr mice, and the generation of donor-derived B cells in the recipient was monitored by determining the immunoglobulin-producing cells developed in the LPS-stimulated cultures of recipient's spleen cells as well as BM cells. As previously stated, the transfer of fresh BM cells resulted in the development of LPS-reactive cells both in spleen and BM simultaneously. On the other hand, when long-term cultured BM cells which were shown to be devoid of B cells and pre-B cells were used as the donor cells, the development of LPS-reactive cells was first observed only in BM, and subsequently in both BM and spleen. The failure to detect LPS-reactive cells in the spleen in the early phase, or day 11 after irradiation and reconstitution, was not attributed to the culture condition or the existence of suppressive activity in day 11 spleen cells. These results indicate that B cell precursors lodge only in the BM of irradiated recipients, grow and differentiate in the same place, and then the differentiated progeny migrate to peripheral lymphoid organs.

Frequency analysis of the antibody specificity repertoire of mitogen-reactive B cells and "spontaneously" occurring "background" plaque-forming cells in nude mice

The antibody specificity repertoire of lipopolysaccharide (LPS)-reactive B cells has been determined in the spleens and bone marrow (BM) of C57BL/Ka athymic nude mice using a limiting dilution culture system that allows the growth and development of every LPS-reactive B cell into a clone of IgM-secreting cells. In addition, the numbers of "spontaneously" occurring ("background") IgM-, IgG-, and IgA-secreting cells as well as the "background" IgM antibody specificity repertoire has been assessed in spleens and BM. The frequencies of antigen-specific LPS-reactive B cells of C57BL/Ka nude and thymus-bearing mice showed a great similarity and ranged from 1 in 1000 to 1 in 2500 for sheep red blood cells (SRBC), horse red blood cells (HRBC), and goat red blood cells (GRBC), from 1 in 10 to 1 in 25 for 5-iodo-3-nitrophenyl-coupled (SRBC), from 1 in 15 to 1 in 150 for 4-hydroxy-3,5-dinitrophenyl-coupled SRBC, and from 1 in 70 to 1 in 140 for 2,4,6-trinitrophenyl-coupled SRBC. The specificity repertoire of the "background" IgM-secreting cells differed from that of age-matched thymus-bearing controls and was different in young and old C57BL/Ka nude mice. Within the limitations of having assessed only a minor fraction of the total B-cell antibody specificity repertoire and supposing that nude mice are largely devoid of functional T cells, the data presented suggest that the generation of the specificity repertoire of newly-formed B cells is hardly or not affected by T cells. On the other hand, T cells do affect the expression of the established repertoire, represented by "background" immunoglobulin-secreting cells.

Idiotypic analysis of potential and available repertoires in the arsonate system

We have shown that, by suitable idiotypic manipulation, BALB/c mice can express the major cross-reactive idiotype (CRI) of A/J mice in response to azophenylarsonate (Ars). In order to know if the CRIA idiotype is present in the potential repertoire of BALB/c before any intentional selection, we used polyclonal activation in vitro and limiting dilution analysis. The readout was done with two monoclonal anti-CRIA antibodies that recognize distinct idiotopes on a CRIA+ A/J germline-encoded monoclonal antibody. We studied the frequency of CRIA+ lipopolysaccharide (LPS)-reactive cells in the spleens of nonimmune and immune A/J mice and in the spleens of naive and manipulated (i.e., producing CRIA+ antibodies) BALB/c mice. A/J and BALB/c naive individuals presented very high frequencies of Ars-specific B cells while the frequency of CRIA+ B cells was only a minor subset (0.5%) of the total Ars-specific subset in the two strains. When A/J mice were immunized with Ars-keyhole limpet hemocyanin, a clear preferential expansion of the CRIA+ minor subset of A/J mice was observed (100x). No such enhancement was observed in BALB/c mice similarly treated. Manipulated BALB/c mice presented a higher frequency of CRIA+ anti-Ars B cells than naive or antigen-immunized BALB/c individuals.

Cellular expression of idiotopes defined by monoclonal antibodies

Monoclonal anti-idiotype (Id) antibodies with specificities for determinants related to the antigen-binding sites of 3 BALB/c myeloma proteins, MOPC-460, HOPC-8 and J558, were used to study Id expression on murine lymphocytes. The monoclonal antibodies were shown to react only with Id structures associated with immunoglobulin on B cells. None of these 3 Id nor a VH Id, detected by a monoclonal antibody made against HOPC-8 heavy chain, were found on T cells. These Id were detected on splenic B cells in neonatal mice; the frequencies in normal, nude and germ-free mice were similar: MOPC-460 Id+: 1.05 +/- 1.7/10(4) spleen cells, HOPC-8 Id+: 1.45 +/- 1.2/10(4) and J558: 0.35 +/- 0.6/10(4). Almost all Id+ cells bore surface IgM, a few expressed surface IgG. MOPC-460 Id+ IgG+ cells were mainly gamma 2a+ or gamma 2b+, whereas J558 and HOPC-8 Id+ IgG+ cells were gamma 3+.

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.

The B cell repertoire revealed by major histocompatibility complex-specific helper T cells. I. Frequencies of a genetically defined V region marker among mitogen- and T helper cell-reactive B lymphocytes in normal and immunized mice

The aim of the present work was to analyze the frequencies of a genetically defined variable (V) region marker in the B cell subset sensitive to T cell help. To this end we used an alloreactive T cell line that has the property of inducing B cells of the appropriate haplotype to exponential growth and polyclonal antibody synthesis. The frequency obtained with this helper line was also directly compared to that obtained with lipopolysaccharide (LPS). We found that in normal BALB/c mice the frequency of M460-positive clonotypes was respectively, 1/100 and 1/1,000 among the T helper- and LPS-sensitive B cell subsets. In mice immunized with antiidiotype coupled to a thymus-dependent antigen, the differences in the numbers of idiotype-positive precursors were even more accentuated, i.e. 1/20 in the B cell subset triggered by T helper cells and 1/800 in those cells responsive to LPS. The frequencies of the M460 determinant in mice immunized with anti-idiotypes coupled to thymus-independent antigens were not significantly different, in either B cell subset, from those obtained with spleen cells of normal nonimmunized animals. Taken as a whole, our results imply that the V gene repertoire revealed by LPS includes precursor distribution, as this distribution occurs during the early stage of B cell development (potential repertoire), while the repertoire revealed by T helper cells includes the V region distribution of those clones that are selected in the periphery of the functional immune system.

Isolation of hybridomas expressing a specific heavy chain variable region gene segment by using a screening technique that detects mRNA sequences in whole cell lysates

A technique is described that allows single hybridoma cell colonies to be assayed for the productive rearrangement of a single immunoglobulin variable region (V) gene segment by utilizing expression of V mRNA for analysis. Hybridomas growing in microwell tissue culture plates are lysed in situ, cellular RNA is directly transferred to nitrocellulose by filtration, and specific immunoglobulin mRNA is detected by hybridization of the filter with a DNA probe. The method is simple and sensitive. A single species of mRNA can be detected in a lysate of 1000 cells; 5000 hybridoma colonies can be easily screened per day. The technique has been successfully used to isolate cell lines from nonimmune mice expressing a particular heavy chain variable region (VH) gene segment.

Heterogeneous and monoclonal helper T cells induce similar anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) antibody populations in the primary adoptive response. II. Lambda light chain dominance and idiotope expression

When the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP) is presented on different carrier molecules, different anti-NP antibody responses are stimulated. On stimulation with NP-lipopolysaccharide (LPS) [T-independent type 1 (TI-1) antigen] kappa + antibodies are the major population, whereas on stimulation with NP-Ficoll [T-independent type 2 (TI-2) antigen], NP-keyhole limpet hemocyanin (KLH) or NP-chicken gamma globulin (CG) [T-dependent (TD) antigens], lambda 1+ antibodies dominate. The relative contribution of idiotopes Ac38 or Ac146 to the lambda 1+ anti-NP response was also different on comparison of TI-1 with TI-2 or TD anti-NP responses. We investigated whether light chain- or idiotype-specific T cells are responsible for these differences. Analysis of the anti-NP response of nude mice after immunization with NP-Ficoll showed lambda 1 dominance. Likewise primary adoptive transfer experiments using carrier-specific T cell lines to reconstitute the TD anti-NP response to NP-KLH or NP-CG, showed that help from carrier-specific T cells alone is capable of stimulating the characteristic lambda 1 dominant response. No significant difference could be found in the levels of Ac38 and Ac146 idiotope expression between mice reconstituted with splenic T cells and those reconstituted with T cell lines. These results suggest that light chain- or idiotype-specific T cells are required neither for the production of lambda 1 light chain dominance, nor for the appearance of idiotopes characteristic of the primary anti-NP response. The possible reasons for differences seen in both light chain and idiotope expression between primary anti-NP responses to the TI-1 antigen NP-LPS and those to TD or TI-2 antigens are discussed.

High frequency of lambda gene activation in bone marrow pre-B cells

The frequency of lambda light chain (L) producing cells in immunoglobulin-producing cells that have been generated in vitro from bone marrow pre-B cells was investigated. The frequency of lambda-producing cells obtained in such a culture was three- to eightfold higher than that observed in the culture of mature spleen B cells. These results suggest that the activation of lambda gene at pre-B cell stage occurs far more frequently than the frequency presumed from the percentage of lambda-bearing cells in mature B cells.

Role of variable region gene expression and environmental selection in determining the antiphosphorylcholine B cell repertoire

To evaluate the role of environmental selective processes, as opposed to variable region gene expression, in the determination of B cell repertoire expression, we have assessed the phosphorylcholine (PC)-specific repertoire of precursor cells that remain in bone marrow cell populations after the removal of surface immunoglobulin (sIg)-bearing cells. Such cells are assumed to represent a stage in B cell maturation before the expression of sIg, and thus at a time when they have not as yet interfaced with environmental influences that operate through sIg receptors such as antigenic stimulation, tolerance, or antiidiotypic regulation. The repertoire as expressed in these cells, therefore, should reflect the readout of immunoglobulin variable region genes as they are expressed in progenitors to B cells. The results of these studies indicate that, as in mature primary B cell pools of BALB/c mice, the majority of PC-responsive sIg- bone marrow cells are of the T15 clonotype. Thus, environmental selective mechanisms would not appear to be required for the high frequency of B cells of the T15 idiotype in the primary B cell repertoire of BALB/c mice. Analysis of the sIg- bone marrow cells in (CBA/N X BALB/c)F1 male mice demonstrated that the deficit of PC-responsive mature B cells, which is a characteristic of this murine strain, must occur after receptor expression, since a normal frequency of PC-responsive and T15-expressing cells is present in their sIg- bone marrow population. Finally, these same mice were used to obtain bone marrow cell preparations from individual leg bones, so as to permit an analysis of the occurrence of T15+ and T15- clonotypes within individual bone marrow populations. The findings from these studies indicate that T15+ B cells occur as a high frequency event within bone marrow generative cell pools. Furthermore, bone marrow populations that are positive for PC-responsive precursor cells often display multiple copies of such precursor cells that are exclusively either T15+ or T15-. This finding indicates that clonal expansion of cells within the B cell lineage apparently occurs before immunoglobulin receptor acquisition.

B cell repertoire diversification precedes immunoglobulin receptor expression

68 monoclonal antibodies specific for the hemagglutinin (HA) of the influenza virus, PR8, were obtained from sIg- bone marrow B cell precursors stimulated in splenic fragment cultures. Reactivity pattern (RP) analysis demonstrated that these anti-HA antibody responses included at least 29 distinguishable clonotypes. Comparison of the specificities of anti-HA antibodies obtained from sIg- bone marrow cells with those obtained from adult spleen cells indicates that the anti-HA repertoires of the two populations are comparable in diversity. Since the sIg- bone marrow B cell precursor pool presumably has not encountered V region-specific regulatory mechanisms in vivo, our data suggest that substantial diversification of the B cell repertoire precedes surface immunoglobulin (sIg) expression and subsequent interaction with environmental regulatory processes.

The immune response against anti-idiotope antibodies II. The induction of antibodies bearing the target idiotope (Ab3 beta) depends on the frequency of the corresponding B cells

In the present study we use two monoclonal anti-idiotope antibodies (Ac38 and Ac146; Ab1) against the germ line-encoded, lambda 1 chain-bearing and (4-hydroxy-3-nitrophenyl)acetyl (NP)-binding antibody B1-8 (Ab1) for the induction of complementary antibodies (Ab3) and ask the question to what extent antibodies bearing B1-8-like idiotopes (Ab3 beta) are represented in the Ab3 population. In this experimental system, Ab3 beta is distinguished from the remaining Ab3 population (Ab3 alpha) by three properties which Ab3 beta may share with B1-8: (a) the binding of NP, (b) the binding to Ac146 (if induced by Ac38) or the binding to Ac38 (if induced by 146) and (c) that they carry lambda 1 chains. Antibodies with all three properties are induced in low amounts by both anti-idiotopes. Also, Ac146 induces only Ab3 alpha (bearing kappa chains and not binding NP and Ac38). In contrast, Ac38 triggers almost exclusively a lambda 1 chain-bearing response, i.e. Ab3 beta. The response has an unusually large size, reaches its maximum after a week and is long-lasting. An analysis at the level of lipopolysaccharide-reactive precursor B cells demonstrates that, in this case, cells expressing Ab3 beta occur at exceedingly high frequency (approximately equal to 10(-3] and are at least 10 times more frequent than cells expressing Ab3 alpha. The high frequency of Ab3 beta-expressing cells correlates with the contribution of several VH, D and J genes to the expression of this particular idiotope. In the case of the Ac146 anti-idiotope antibody, the response is dominated by Ab3 alpha. Ab3 beta represents less than 10% of the total response, reaches maximal levels 2 weeks after immunization and declines rapidly. This correlates with a low frequency of precursor B cells expressing Ab3 beta (approximately equal to 10(-5] and a restriction of the corresponding idiotope to rare VH-D combinations, caused presumably by a stringent contribution of the H chain to this idiotope which covers the NP-binding site. Our data suggest that anti-idiotypic antibodies (Ab2) against Ab1 will preferentially induce antibodies idiotypically related to Ab1 if the corresponding idiotopes are expressed in high frequency in the B cell compartment. This is expected in cases where Ab2 recognizes an idiotope that can be formed by many germ line-encoded VH-D-VL-combinations.

Symmetry and asymmetry in idiotypic interactions

At the level of antibody molecules, the partners in an idiotypic interaction are functionally equivalent, and the distinction between "idiotype" and "anti-idiotype" is merely operational. This point must be taken into account in the interpretation of regulatory experiments with "idiotypic" and "antiidiotypic" antibodies. Indeed, consistent interpretations of certain sets of data can be obtained if "idiotype" and "antiidiotype" are used as operational terms for functionally equivalent molecules with complementary binding sites. For interacting antibody populations, symmetrical and asymmetrical situations can occur. The latter case is when an antibody family whose members express a set of idiotypes in various combinations--a typical situation in germ-line encoded immune responses--interacts with a heterogenous population of anti-idiotypes, the common denominators of which are binding sites for the common idiotopes expressed in the idiotypic antibody family. Through this type of interaction, one can explain in a first approximation the experiments of Urbain, Cazenave and others in which antiidiotypic antibody populations (ab2) induce antibodies (ab3) which resemble the original idiotypic population (ab1) idiotypically, but not primarily in antigen-binding specificity. Such a model would also describe an idiotypic network in which germline-encoded recurrent idiotypes (expressed in antibody families of the type described above) interact with anti-idiotypes generated by somatic mutation.

The selection and maintenance of the V region determinant repertoire is germ-line encoded and T cell-independent

The number of lipopolysaccharide-sensitive precursor cells synthesizing immunoglobulin (Ig) which reacts with the monoclonal anti-M460 antibody F6(51) has been determined in the spleen and in the bone marrow of different strains of mice. These precursor frequencies fall into two quantitatively different groups. The first group includes mice with the same Igh haplotype as BALB/c animals (Igha). In this group, spleen cells contained between 1:10(4) to 1:5 X 10(4) B cell precursors secreting Ig which bound F6(51). The second level of precursor was obtained with animals with allotypic haplotypes other than Igha. These values were too low to allow accurate frequency determinations. The frequency of these cells in mice of the latter group, however, increased dramatically when these animals were hyperimmunized with the monoclonal anti-M460 antibody. Similar results were obtained when the frequencies were determined using the Ig- fraction of bone marrow cells. Surprisingly, the numbers of lipopolysaccharide-sensitive B cell precursors secreting F6(51)-binding Ig in spleen cells of nude mice was found to be similar to the one in splenocytes of normal mice, and even in this case, the frequencies reflected the genetic background of the animals tested. Taken together these data support the notion that the establishment and the maintenance of the M460 idiotypic repertoire is germ-line encoded and independent of regulatory T cells.