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

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.

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.

A common idiotope on T cell receptors and antibodies expressed in the absence of network selection

The monoclonal antibody F6(51), directed to an idiotope of MOPC 460-like anti-1,4,6-trinitrophenl (TNP) antibodies produced in IgHa mouse strains, identifies in helper T cells from C57BL/6 (IgHb) mice with (4-hydroxy-3-nitrophenyl)acetyl (NP)-self specificity, a clonotypic determinant functionally and biochemically associated with the specific T cell receptor. The expression of this antibody-related T cell clonotype in C57BL/6 mice, although "recurrent", is independent of network selection, as shown by its presence in B mice suppressed from birth with anti-mu antibodies, and in IgH-congenic mouse strains. These results indicate aleatory cross-reactivity between T cell receptors and antibodies and command caution in network interpretations for "idiotype sharing".

Turning (Ir gene) low responders into high responders by antibody manipulation of the developing immune system

The ability of helper T cells directed against trinitrophenyl-modified syngeneic spleen cells to recognize low-hapten densities on target cells is under major histocompatibility complex-linked Ir gene control. Thus, BALB/c (H-2d) mice are low responders while H-2 congenic BALB.C3H (H-2k) mice are high responders. Immunization of adult BALB/c mice with the monoclonal antibody F6(51), directed to shared idiotopes by anti-trinitrophenyl antibodies and clonal receptors on anti-trinitrophenyl-self helper T cells, leads to the production of high titers of circulating idiotype, has no influence on helper T cell idiotypic profiles, but shifts to a high-responder phenotype the ability of helper T cells to recognize low-hapten densities. These effects on Ir gene phenotype are even more striking in untreated progenies from F6(51)-immunized BALB/c females, which are better responders than genetically high-responder BALB.C3H mice, although completely different in the expression of the F6(51)-defined clonotype. The general significance of these findings on Ir gene-directed T-cell repertoire selection is discussed, for they constitute formal evidence against antigen-presentation as a mechanism of Ir gene effects and strong support for the importance of maternal influences on the development of T-cell repertoires.

Clonal analysis of the anti-DNA repertoire of murine B lymphocytes

The present studies characterize at the clonal level the repertoire of lipopolysaccharide-responsive murine B lymphocytes committed to the production of antibodies reactive with denatured DNA. This repertoire is vast in normal mice as 1-5% of total mitogen-induced antibody-forming cell clones secreted denatured DNA-reactive antibodies when the splenocyte donors were CBA (Ighj), BALB/c (Igha), C57BL/6 (Ighb), CBA nu/nu, and C57BL/6 nu/nu athymic mice. The autoimmune NZB (Ighe) strain did not display elevated proportions of anti-denatured DNA antibody-forming cell precursors. Cross-reactions shown by CBA anti-denatured DNA antibodies suggest that many antibodies might derive significant binding energy from interaction with the bases or similar hydrophobic moieties. Cross-reactions with other tested polynucleotides were frequent, but cross-reactions with phospholipids and phosphocholine were undetectable. Most anti-DNA antibodies bound preferentially or exclusively to single-stranded denatured DNA as compared to double-stranded native DNA. The frequency of anti-denatured DNA antibody-forming cell precursors among CBA peritoneal cells was not elevated. Fluorescence-activated cell sorter-selected Ly-1-positive NZB splenic B cells were not enriched, and Ly-1 negative B cells were not depleted of anti-DNA antibody-forming cell precursors. These results show that antibody-forming cell precursors specific for denatured DNA are not restricted to the Ly-1 positive B-cell subset.

Murine lupus anti-DNA antibodies cross-react with the hapten (4-hydroxy-5-iodo-3-nitrophenyl)acetyl, but immunization-induced anti-DNA antibodies do not

The antigen-binding selectivity of 2 sets of anti-DNA antibodies from autoimmune mice and from normal mice was examined. Eighteen affinity-purified anti-DNA auto-antibodies from MRL-lpr/lpr mice were examined for binding to the haptens azobenzenearsonate, phosphorylcholine, (4-hydroxy-3-nitrophenyl)acetyl and (4-hydroxy-5-iodo-3-nitrophenyl)acetyl (NIP). Five of these autoantibodies bound to NIP-protein conjugates. In contrast, none of 12 monoclonal antibodies to single-stranded DNA or left-handed Z-DNA induced by immunization of BALB/c and C57BL/6 mice with nucleic acid antigens reacted with the tested haptens. In a reciprocal test of the relationship between anti-DNA and anti-NIP binding, we examined 24 monoclonal antibodies to NIP, from various strains of mice, for binding to DNA. One such antibody from a BALB/c mouse also bound to DNA. These results are discussed in the context of the mechanisms underlying autoantibody hyperproduction.

A synthetic vaccine constructed by copolymerization of B and T cell determinants

Synthetic vaccines are based on the identification of short peptide sequences responsible for inducing a protective immune response. These sequences could contain B and/or T cell determinants. In this study, we have examined the recognition by B and T mouse lymphocytes of several synthetic peptides corresponding to regions of a bacterial and two viral proteins. These include a streptococcal S-34 peptide, H(99-121) and two other synthetic hepatitis B virus surface peptides. A lymph node proliferation assay was employed to detect T cell determinants. Limiting dilution analysis was used to estimate the frequency of clonal precursor B cells specific for an antigenic determinant. This study indicates that the synthetic hepatitis B virus surface peptides are recognized by B cells but not by T cells, whereas the S-34 peptide possesses both B and T epitopes. The copolymerization of the B determinant H(99-121) with S-34 has conferred immunogenicity to the H(99-121) peptide. After copolymerization, the synthetic hybrid molecule retained the S-34 T epitope and acquired a new determinant recognized by T cells. These results demonstrate that synthetic vaccines could be constructed by appropriate selection and organization of B and T determinants.

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.

Repertoire of murine lambda-positive variable domains: polyclonal induction of lambda isotypes and their associated pattern of antibody specificities

The diversity of lambda variable (V lambda) domains is extremely restricted when compared to those of VH and V kappa. In addition, each V lambda domain is determined by the C lambda domain. For these reasons, the lambda system is an excellent model for the study of the associated VH region repertoire. The study of V lambda domain diversity has been limited by the small contribution (approximately 5%) of lambda-bearing proteins to the total Ig pool. We now show that treatment of BALB/c mice with rabbit anti-lambda 1 antibodies coupled to lipopolysaccharide induces a production of polyclonal lambda 1 light chain-bearing Ig whereas, conversely, treatment with rabbit anti-lambda 2 antibodies induces a production of polyclonal lambda 2 + lambda 3 light chain-bearing Ig. The antigenic specificities of these two distinct lambda populations were then studied using B1355 dextran, (4-hydroxy-3-nitrophenyl)acetyl (NP) and 2,4-dinitrophenyl (DNP) as antigens. The anti-alpha(1-3)dextran antibody specificity was found to be mediated exclusively by antibodies bearing the lambda 1 isotype whereas the anti-NP and anti-DNP antibody specificities are mediated by both the lambda 1 and lambda 2 + lambda 3 isotypes. In addition, various mouse strains with the VHa or VHb allotypic haplotype and the rlo lambda 1 or r+ lambda 1 phenotype were treated with rabbit anti-lambda 1 antibodies. The lambda 1 anti-NP and anti-DNP antibody specificities were similar in all strains whereas the lambda 1 anti-alpha(1-3)dextran specificity was linked to the presence of the VHa allotypic haplotype. The mouse strains with the rlo lambda 1 or r+ lambda 1 phenotype did not differ in terms of their patterns of lambda 1 antibody specificities.

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.

The expression of a private idiotope requires pretreatment with noncomplementary anti-idiotypic antibodies

The levan-binding ABPC48 myeloma protein is characterized by 3 idiotopes, (Ids), defined by 3 syngeneic monoclonal anti-idiotypic antibodies (IDA 10, IDA 16 and IDA 17). When BALB/c mice are immunized with levan, they produce anti-levan antibodies, some of which carry the Id 10 and Id 16 but not the Id 17 determinants. In the present study, we attempted to induce the synthesis of Id 17 positive anti-levan molecules. We found that immunization with IDA 17 antibodies alone was ineffective in inducing an Id 17 positive anti-levan response. By contrast, successive immunizations with IDA 10, IDA 16 and IDA 17 antibodies resulted in the synthesis of Id 17 positive anti-levan immunoglobulins. The synthesis of these molecules was concommitant with the induction of Id 10 and Id 16 positive anti-levan antibodies. Thus our data suggest that the Id 17 determinant on anti-levan antibodies is coexpressed with Id 10 and Id 16, and that successive anti-idiotypic treatment may result in the selective expansion of rare ABPC48 cross-reactive idiotype B-cell clone precursors.

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.

Immune response induced by a single or several syngeneic monoclonal antiABPC48 antiidiotypic antibodies: no predominant coexpression of ABPC48 idiotopes

BALB/c mice were immunized with monoclonal BALB/c antibodies IDA10, IDA16 and IDA17 raised against the BALB/c ABPC48 myeloma protein. Several procedures of immunization--copolymers with lipopolysaccharide or keyhole limpet hemocyanin, simultaneous or sequential injections of different IDAs--were performed in an attempt to orient the immune response towards the production of ABPC48-like idiotypes. We used a binding assay which identifies two idiotopes on the same molecule to measure the population of antibodies induced in these responses. The expression of ABPC48 cross-reactive idiotypes in immune sera was analyzed. The results show that, with all immunization protocols, immune responses to different monoclonal antiidiotypic antibodies are mostly independent of each other: the coexpression of ABPC48 idiotopes, either private or recurrent on the induced antibodies, is rarely found; it makes it difficult to discriminate by a serological approach between cross-reactive idiotypes and anti-antiidiotypic antibodies. We discuss the interest of combining molecular and serological approaches to identify these two populations of antibodies.

Molecular analysis of induced idiotypes associated with autoanti-thyroglobulin

Idiotype (Id) and autoanti-thyroglobulin were induced in different strains of mice by priming with anti-Id to monoclonal anti-thyroglobulins (D8 and G4) and challenged with a subimmunogenic dose of thyroglobulin (Tg). Both D8.Id and G4.Id were induced in CBA mice by priming with the appropriate anti-Id, but only priming with anti-D8.Id also induced an increase in anti-Tg. D8.Id was induced in other strains by the same schedule but it only appeared to be associated with anti-Tg in 129 and, to a lesser extent, BALB/c mice, both of which have the allotype Iga. The extent of the overlap between the D8 Id and the anti-Tg was estimated and shown to be greatest in the CBA strain from which the D8 clone was originally derived. Spectrotypic analysis of the induced Ids in CBA mice showed that some of the D8.Id, but none of the G4.Id, was identical to the original clonotype, implying that CBA mice normally have cells which can be induced to produce D8.Id-positive autoanti-Tg, which are normally weakly expressed or regulated. The observation that anti-D8.Id priming in some strains increased D8.Id-negative anti-Tg responses suggests that the D8.Id may also be associated with anti-Tg T-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.

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.

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.

Incomplete expression of the MOPC 460 idiotype in the sera of BALB/c mice immunized either with DNP antigen or with anti-idiotypic antibodies

The MOPC 460 idiotype, as defined by polyclonal probes, has been described as a recurrent marker among the anti-DNP antibodies synthetized by IghCa mice. In this paper, we demonstrate, using syngeneic monoclonal anti-idiotypic probes, that only a part of the idiotopes of this idiotype are indeed recurrently expressed in BALB/c mice (IghCa) after immunization with DNP antigen. We will also show that the immunization of BALB/c mice with monoclonal anti-idiotypic antibody specific for the recurrent determinant results firstly in the synthesis of anti-DNP antibodies and secondly in the expression of the same recurrent M460 idiotope present on a part of induced anti-DNP molecules. Contrary to this, the immunization with the monoclonal anti-idiotypic antibody specific for the private idiotope never resulted in the synthesis of anti-DNP antibodies. These results clearly suggest that, after DNP or anti-idiotypic immunization, the M460 idiotype is not expressed in its entirety.

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 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

An analysis is presented in which we measure the expression of a subset of antibody variable (V) regions in lipopolysaccharide (LPS)-reactive precursor B cells at various stages of ontogeny. The V regions were characterized by hapten (4-hydroxy-3-nitrophenyl)acetyl (NP)-binding specifity and/or expression of idiotypic determinants whose genetic basis had been explored in previous studies. Only V regions containing the V lambda 1 domain were considered: this allowed an unequivocal determination of idiotopes and reduced heterogeneity in the system essentially to the multiplicity of VH and D genes. It was found that approximately every fourth lambda 1-bearing LPS-reactive splenic B cell produces an NP-binding antibody. Approximately 1 in 40 lambda 1-bearing cells expressed an idiotope (Ac38) which is encoded by V lambda 1 and a set of related VH genes in combination with D and J elements. Of these cells, only a minority produce an NP-binding antibody and a few percent of the latter express a second idiotope (Ac146) which is known to be restricted to a subset of Ac38-positive, NP-binding humoral antibodies. All these frequencies are in good accord with previous analyses of anti-idiotope-induced antibodies in the serum. They can be easily accommodated into a simple model of random selection of VH genes in LPS-reactive B lymphocytes. The frequencies of the V regions under study were essentially the same in LPS-reactive B cells from spleens of adult and newborn animals and in LPS-reactive B cells generated from bone marrow pre-B cells in vitro. In the case of the latter cells the frequencies were independent of the absence or presence of T cells in the culture system. While we could thus detect, in naive mice, neither positive nor negative selection of the cells from the time of their generation in the bone marrow until their arrival in the periphery, negative selection is in principle possible: the presence of microgram amounts of anti-idiotope antibodies during maturation from pre-B to B cells specifically blocks the appearance of idiotope-bearing LPS-reactive cells in vitro. The potential physiological role of the latter effect in the sense of self-stabilization of the expressed antibody repertoire in ongoing immune responses and the possibility that frequency determinations in LPS-reactive B cells may be not representative for the repertoire expressed in the population of mature B cells is discussed.