Monoclonal rat antibodies to murine IgM determinants

Isolation of Ly-1+/CD5+ B cells by cell sorting

Ly-1/CD5 is a 68-kDa glycoprotein that was originally thought to mark the helper subset of T cells. Later it was shown to be present on all T cells and, more recently, on a subset of B cells. Although its function remains the subject of speculation, CD5 expression serves as a useful marker for a functionally distinct population of B cells that has attracted a considerable amount of interest from investigators of both murine and human immune systems. Of critical importance in much of this work is the isolation of pure populations of CD5+ B cells along with appropriate control populations. A flow cytometry technique is presented in this unit, which results in the selection and isolation of two populations of cells from a complex mixture based on physical properties (e.g., size and internal granularity) and correlated expression of several surface molecules.

IFN-alpha/beta enhances BCR-dependent B cell responses

Type I interferon (IFN-I) is constitutively produced in the bone marrow (BM), and induced at sites of inflammation and following infection by viruses or microorganisms. We have previously shown that IFN-I regulates the generation and selection of normal B cell populations in the BM. In the present work, we assess the effects of IFN-I on mature B cell function by monitoring the responses of IFN-alpha/beta-treated murine splenic B cells to apoptotic, mitogenic and activating stimuli. A similar analysis is performed on BM mature B cells obtained from wild-type or IFN-I receptor-deficient mice. IFN-alpha/beta is shown to induce B cells to a state of partial activation characterized by the up-regulation of CD69, CD86 and CD25 molecules in the absence of either proliferation or terminal differentiation. B cells treated with IFN-alpha/beta show an increased survival and resistance to Fas-mediated apoptosis. IFN-alpha/beta also enhances B cell responses to BCR ligation such as calcium fluxes, IgM internalization, induction of activation markers and proliferation. These results indicate that in addition to its inhibitory effect on viral replication and T cell apoptosis, IFN-alpha/beta plays an essential role during an inflammatory response by lowering the threshold for B cell induction, thereby promoting fast and polyclonal antibody responses.

Cross-linking surface Ig delays CD40 ligand- and IL-4-induced B cell Ig class switching and reveals evidence for independent regulation of B cell proliferation and differentiation

T cells stimulate B cells to divide and differentiate by providing activating signals in the form of inducible membrane-bound molecules and secreted cytokines. Provision of these signals in vitro reproduces many of the consequences of T-B collaboration in the absence of any form of Ag stimulation. Although clearly not obligatory, Ag signals appear to play an important regulatory role in numerous aspects of the B cell response. To examine directly the effect of an Ag signal, naive B cells were stimulated in the presence of rCD40 ligand, with or without IL-4 in the presence or absence of different anti-Ig mAbs. Anti-Ig mAbs exerted variable effects on the B cell division rate, from enhancement to no effect to inhibition. In contrast, all anti-Ig mAbs tested inhibited division-linked isotype switching to IgG1 and IgE. Thus, B cell Ag receptor ligands could modify the rates of B cell expansion and class switching independently. The ability of anti-Ig reagents to modify class switching suggests the B cell Ag receptor may play an important role in the selection of Ig isotypes during T cell-dependent humoral immune responses to Ags of different physical structure.

P, Martínez-M. JA, Morales-A. S, Copín SG, Marcos MAR, Gaspar ML. Differential Involvement of the Transcription Factor Blimp-1 in T Cell-Independent and -Dependent B Cell Differentiation to Plasma Cells

Along humoral immune responses, different stimuli drive the differentiation of B lymphocytes to Ig-secreting plasma cells in discrete microenvironments. The Blimp-1 transcription factor is up-regulated early during the transition of mature B cells to IgM-secreting plasma cells. In the present study, we have examined the requirement of Blimp-1 in plasma cell formation after both T cell-independent (LPS) and -dependent (CD40 + IL-4, Th cell lines) stimulation of spleen B cells. B lymphocyte-induced maturation protein (Blimp-1) was expressed early after in vitro LPS stimulation, mainly in a population of IgM+Syndecan+CD43+ preplasma cells. In contrast, the BSAP transcription factor expressed in mature B cells was down-regulated during the differentiation to plasma cells. Treatment of these cultures with Blimp-1-specific antisense phosphorothioate oligonucleotides suppressed both Blimp-1 protein levels and the emergence of IgM+Syndecan+ cells and plasma cells. However, T-B cell cocultures of spleen B cells from C3H/HeJ (H-2k) mice and syngeneic autoreactive SR.10 Th2 cells submitted to the anti-Blimp-1 therapy did not show any significant reduction in IgM- and IgG1-secreting plasma cell formation. Spleen B cells treated with anti-CD40 mAb + IL-4 differentiated to IgG1-secreting cells without significant transcription of the Blimp-1 gene; anti-Blimp-1 treatment subsequently did not have any effect in the later cultures. Altogether, these results suggest that Blimp-1 transcription factor specifically promotes T cell-independent B cell differentiation to plasma cells, probably at preplasma cell stages. In contrast, T cell-dependent plasma cell formation likely evolves through Blimp-1-independent pathways.

Role of positive and negative cis-regulatory elements in the transcriptional activation of the lysozyme locus in developing macrophages of transgenic mice

Expression of the chicken lysozyme locus in macrophages is regulated by at least six different positive and negative cis-regulatory elements. Chromatin of the chicken lysozyme locus is gradually reorganized during macrophage differentiation, indicating that each cis-regulatory element is activated at a different developmental stage. Irrespective of their differential developmental activation, individual cis-regulatory regions are capable of driving transcription of the lysozyme gene in mature macrophages of transgenic mice. In order to examine the role of different cis-regulatory regions in lysozyme locus activation, we analyzed the time course of transcriptional up-regulation of deletion mutants of the lysozyme locus in a new in vitro differentiation system based on enriched primary macrophage precursor cells from the bone marrow of transgenic mice. We show that constructs carrying cis-regulatory elements which are structurally reorganized early in development are also transcriptionally active at an early stage. A construct in which the early enhancer has been deleted shows a delay in transcriptional activation. The presence or absence of a negative regulatory element has no influence on the time course of transcriptional activation of the lysozyme locus.

Expression of HIS50 Ag: a rat homologue of mouse heat-stable antigen and human CD24 on B lymphoid cells in the rat

Recently, a cDNA encoding a newly identified rat antigen (HIS50 Ag) that binds to monoclonal antibody (mAb) HIS50 was cloned and shown to be homologous to cDNA encoding murine heat-stable antigen (HSA) and human CD24. Here we show that, like CD24 and HSA, at least part of HIS50 Ag is inserted into the plasma membrane by a glycosylphosphatidylinosito: (GPI)-lipid linkage and we describe its expression in rat haemolymphopoietic tissues. HIS50 Ag expression was almost exclusively confined to B lymphoid cells, the vast majority of T lymphoid cells, erythroid and myeloid cells were HIS50+. Cell suspension analysis indicated that in bone marrow (BM) almost all Thy-1+ cells, HIS24+ cells [HIS24 recognizes the B-cell form of leucocyte common antigen (LCA)], terminal deoxynucleotidyl transferase-positive (TdT+) cells and (c + s)kappa cells expressed HIS50 Ag, and all (c + s)mu 1 cells. A presumably early population of B lymphoid cells, expressing HIS24 Ag without HIS50 Ag, TdT or immunoglobulin HIS24+HIS50+ TdT Ig+), constituted 1.6% of BM nucleated cells. In blood, one-fifth of mononuclear cells were HIS50+, and about 85% of these expressed mu and/or kappa chains. In spleen, flow cytometry analysis and immunohistology demonstrated heterogeneous expression of HIS50 Ag: immunoglobulin M (IgM)bright cells (as found largely in red pulp and marginal zone) were HIS50bright, while IgMdull cells expressed low or undetectable levels of HIS50 Ag. Germinal centre B cells expressed high levels of HIS50 Ag. Germinal centres of lymph nodes and tonsil of man also bound HIS50. We conclude that HIS50 Ag expression in the haemolymphopoietic system of rat is virtually restricted to the B lineage.

Increased sensitivity to apoptotic stimuli in c-abl-deficient progenitor B-cell lines

The protooncogene c-abl encodes a nonreceptor tyrosine kinase whose cellular function is unknown. To study the possible involvement of c-Abl in proliferation, differentiation, and cell cycle regulation of early B cells, long-term lymphoid bone marrow cultures were established from c-abl-deficient mice and their wild-type littermates. Interleukin 7-dependent progenitor B-cell clones and lines expressing B220 and CD43 could be generated from both mutant and wild-type mice. The mutant and wild-type lines displayed no difference in their proliferative capacity as measured by thymidine incorporation in response to various concentrations of interleukin 7. Similarly, c-abl deficiency did not interfere with the ability of mutant clones to differentiate into surface IgM-positive cells in vitro. Analysis of cultures after growth factor deprivation, however, revealed a strikingly accelerated rate of cell death in c-abl mutant cells, due to apoptosis as confirmed by terminal deoxynucleotidyltransferase-mediated UTP nick end labeling analysis. Furthermore, a greater susceptibility to apoptotic cell death in c-abl mutant cells was also observed after glucocorticoid treatment. These results suggest that mutant c-Abl renders the B-cell progenitors more sensitive to apoptosis, and may account for some of the phenotypes observed in c-abl-deficient animals.

Studies on the T cell dependence of natural IgM and IgG antibody repertoires in adult mice

The present experiments address the thymic dependence of IgM and IgG natural antibody repertoires in adult euthymic and athymic BALB/c mice, as well as in athymic animals reconstituted with a fixed number of syngeneic T cells. Within 3 weeks of the transfer of 10(7) syngeneic splenic T lymphocytes to athymic mice, the T cell compartment is essentially reconstituted in the peritoneal cavity (up to 80% of the numbers in euthymic animals), but is only 10-20% of controls in the spleen and lymph nodes. Early after transfer, there is an increase in the numbers of activated B cells and of immunoglobulin-secreting cells in the spleen, and within 1-2 weeks, the serum concentrations of IgG1 and IgG2a are fully reconstituted to control levels (30-40-fold increased). Multiparametric analyses of serum IgM and IgG repertoires revealed that euthymic and athymic mice share essentially all natural antibody reactivities towards syngeneic extracts of liver and muscle. When tested at the same immunoglobulin concentrations, however, nude sera consistently show higher values of reactivity in all detectable bands. The transfer of 10(7) splenic T cells into athymic mice results in a general decrease of serum IgM reactivities, some of which become undetectable, and in alterations of the serum IgG repertoire as early as 1 week, and for at least 4 weeks after transfer. T cell transfer, however, fails to restore the euthymic IgM and IgG repertoires within 4 weeks. The present observations demonstrate that, after limited T cell reconstitution of nude mice, there is a rapid and quantitatively important increase of serum IgG1 and IgG2a production; the serum IgM reactivity repertoire is qualitatively similar in euthymic and athymic animals, but is generally decreased by T cell activity; and the serum IgG repertoire, which is qualitatively similar in euthymic and athymic animals, is amplified by T cell activity and partially altered by T cell transfer into athymic animals. These results raise questions on the mechanisms of B cell activation and natural antibody repertoire selection in T cell-deficient adult individuals.

Bcl-2 increases memory B cell recruitment but does not perturb selection in germinal centers

To address the role of apoptosis in the humoral immune response, we have examined a well-characterized T cell-dependent B cell response in mice expressing transgenic Bcl-2 in their B lymphocytes. The selection of somatic mutants and the appearance of high affinity antibodies was not affected by constitutive Bcl-2 expression. Such expression did, however, disproportionately increase the antigen-specific memory B cell pool, suggesting that the final size of the memory compartment may be regulated by an apoptotic process, which, in turn, can be influenced by Bcl-2. In addition, transgenic mice showed prolonged survival of foci of early antibody-producing cells, suggesting their removal is mediated by apoptosis that can be blocked by Bcl-2.

The role of B cells in lpr/lpr-induced autoimmunity

The primary roles of T cells and B cells in the initiation of systemic autoimmunity are unclear. To investigate the role of B cells, we crossed the "Jh knockout" mutation onto the autoimmune lpr/lpr background. Animals homozygous for both traits were obtained. As expected, these animals lack B cells. These animals also show no signs of autoimmune kidney destruction nor vasculitis, in spite of carrying the lpr/lpr mutation. In contrast, lpr/lpr littermates that had B cells had severe nephritis and vasculitis, as well as autoantibodies. These results demonstrate a primary role for B cells and/or (auto)antibodies in initiating several types of autoimmune-mediated tissue destruction. The implications of this finding for models and therapy of autoimmunity are discussed.

Expression of HLA-DR4 and human CD4 transgenes in mice determines the variable region beta-chain T-cell repertoire and mediates an HLA-DR-restricted immune response

Inherited susceptibility to rheumatoid arthritis is associated with genes encoding the human major histocompatibility complex class II molecule HLA-DR4. To study the immune function of HLA-DR4 and attempt to generate a murine model of rheumatoid arthritis we have produced triple transgenic mice expressing HLA-DRA*0101, -DRB1*0401, and human CD4. The expression of the HLA transgenes is driven by the promoter of the murine major histocompatibility complex class II I-E alpha gene and was found on murine cells that normally display major histocompatibility complex class II molecules. The expression of the human CD4 transgene is driven by the murine CD3 delta-promoter, and therefore its gene product was found on cells that express murine CD3. In contrast to other HLA-DR and HLA-DQ transgenic mouse lines, the transgenes are functional in our mice. In H-2 I-E-negative transgenic mice, T cells expressing variable region beta chain (V beta) 3, 5, 6, 7, 9, 11, 12, or 13 were either absent or significantly reduced, in contrast to H-2 I-E-negative nontransgenic littermates. In addition, the peptide antigen influenza A virus hemagglutinin 307-319, which binds to the HLA-DRA*0101/-DRB1*0401 heterodimer with high affinity and induces an HLA-DR-restricted and CD4+ T-cell response in humans, also induced a T-cell response in the triple transgenic mice but not in nontransgenic littermates. Thus, these transgenic mice should permit extensive testing of the antigen-presentation capabilities of the HLA-DRA*0101/-DRB1*0401 molecule.

Isolation of peritoneal precursors of B-1 cells in the adult mouse

Two weeks of daily peritoneopheresis of adult mice result in the selective depletion of B-1 cells, followed by the appearance of a population of B220+IgM-lymphocytes in the peritoneal cavity. These cells share with bone marrow (BM) pre-B cells expression of lambda 5, VpreB, and RAG-1 genes and a higher fraction of unrearranged V to DJ heavy (H) chain immunoglobulin (Ig) gene segments, when compared with mature B lymphocytes. Upon transfer to SCID recipients, sorted peritoneal B220+IgM- cells fail to colonize the BM, repopulate very few B cells in the spleen, but entirely reconstitute the B-1 cell compartment in the peritoneal and pleuropericardial cavities. In contrast, parallel transfers of sorted BM and pleuropericardial cavities. In contrast, parallel transfers of sorted BM B220+IgM- cells result in reconstitution of the BM and spleen B lineage cell compartments, but in no coelomic B cell repopulation. Both types of pre-B cells reconstitute splenic plasma cells of donor origin, but with markedly distinct efficiencies: the ratio of IgM-plasma cell/B cell numbers in the spleens of peritoneal pre-B cell recipients is more than 500-fold higher than that of recipients reconstituted by BM pre-B cells. We take these data to indicate that (1) differentiative commitment to the B-1 cell population occurs before selection events on mature cells; (2) B-1 precursors exist or may be locally produced in the adult mouse; (3) there is a lineage-related differential ability of mature B cells to undergo terminal differentiation to high-rate Ig secretion.

Reactivity and structure of a mouse anti-F(ab')2 IgM. Comparison of its variable region sequences with those of a structurally close polyreactive natural IgM

IE12 is a monoclonal IgM with strong anti-F(ab')2 activity that inhibits the binding of normal mouse IgG to self antigens. In this study, we found that this IgM was also reactive with several monoclonal antibodies (mAbs), myeloma proteins and B lymphocytes from normal BALB/c mouse. The nucleotide sequences of the variable region of the heavy and light chains of IE12 were determined, and compared to those of another mAb already described in the literature. This mAb uses the same light chain and also the same VH, D and JH segments, but unlike IE12, is polyreactive. The comparison of the amino acid composition of these two mAbs and of the computer predictions for their structure and hydrophilicity indicated that the most striking difference between them was located in the third complementarity determining region (CDR3) of the heavy chain. Indeed, they used the same D segment but translated in two different reading frames, leading to different amino acid compositions. The CDR3 of IE12 contains aliphatic amino acids, while that of the polyreactive IgM does not. In addition, IE12 has two prolines, one at each at each extremity of its D segment, that could confer a certain rigidity to this region. Finally, the CDR3 of IE12 is predicted to be hydrophobic, while the one of the polyreactive IgM is predicted to be hydrophilic and more flexible, suggesting that the hydrophilicity and the flexibility of this region might be critical for polyreactivity.

H-2z homozygous New Zealand mice as a model for B-cell chronic lymphocytic leukemia: elevated bcl-2 expression in CD5 B cells at premalignant and malignant stages

In New Zealand mice, the major histocompatibility complex (MHC) controls the development of both autoimmune disease and B cell chronic lymphocytic leukemia (B-CLL). While H-2d/H-2z heterozygosity acts as one major predisposing genetic element for autoimmune disease, H-2z/H-2z homozygosity acts as an element for B-CLL. In the H-2z/H-2z homozygotes, there was an age-dependent increase in frequencies of CD5 B cells in the blood and spleen, and such CD5 B cells showed oligoclonal to monoclonal expansion, giving rise to B-CLL. B-CLL cells from these mice had surface phenotypes typical of CD5 B lineage cells, and expressed high levels of proto-oncogene bcl-2. Elevated bcl-2 expression was also observed in premalignant B cells in the aged mice, thereby suggesting that apoptosis-resistant, long-surviving CD5 B cells with a self-renewal capacity form the basis of malignant transformation. This model not only provides clues for analyzing multiple steps of genetic alterations involved in the generation of B-CLL, but also sheds light on the correlation between B-CLL and autoimmune disease.

Peripheral lymphoid hyperplasia and central lymphoid depletion in mice treated with a bacterial B-cell mitogen (F3'EP-Si/p90)

In order to further understand the mechanism mediating the mitogenic and immunosuppressor effects of p90, a protein produced by Streptococcus intermedius, flow cytometric studies were performed on peripheral and central lymphoid organs of mice treated with this protein. p90 induced a strong blastogenic B-cell response in the spleen and lymph nodes, followed by a slight but significant polyclonal T-cell activation. B-cell repertoire analysis indicated that polyclonal B-cell responses affected similarly both CD5+ and conventional (CD5-) B cells in the spleen. Repertoire analysis of T cells failed to reveal any preferential stimulation of the V beta T-cell receptor (V beta-TcR) families studied. Peripheral lymphoid hyperplasia was observed concomitantly with central lymphoid depletion. In the bone marrow, pre-B and B cells were profoundly depleted, with a more pronounced effect on small pre-B cells. In the thymus, double-positive (CD4+CD8+) thymocytes were preferentially eliminated, with a relative enrichment of single positive (either CD4+ or CD8+) and double-negative (CD4-CD8-) thymocytes.

Differential sensitivity to interleukins of CD5+ and CD5- anti-DNA antibody-producing B cells in murine lupus

We studied the effects of interleukins (IL) on in vitro IgM and IgG anti-DNA antibody production by splenic B cells from autoimmune disease-prone NZBxNZW (NZB/W) F1 mice. It was found that different interleukins regulate phenotypically distinct B cells producing separate isotype of anti-DNA antibodies. IL-2 slightly but significantly inhibited the production of IgM anti-DNA antibodies. IL-4 and IL-6 significantly enhanced the antibody production, but the effects were not so marked and inconsistent, particularly with respect to IL-6. By contrast, the effects of IL-5 were remarkable, particularly on splenic B cells from young mice. As for IgG anti-DNA antibodies, IL-6, but not other interleukins, markedly up-regulated the antibody production by splenic B cells from mice over 6 months of age, in a dose dependent fashion. Thus, the ability of B cells to produce IgG anti-DNA antibodies appears to be dependent on the surface expression of IL-6 receptor (IL-6R) at the ages when the mice begin to develop the disease. Studies of the surface phenotypes showed that while the IL-5-sensitive major IgM anti-DNA producers were CD5+Lp-3(CD43)-sIgM+, the IL-6-sensitive major IgG anti-DNA producers were CD5-Lp-3+sIgM-. However, significant amounts of IgG antibodies were also produced, in the presence of IL-6, by CD5+Lp-3+sIgM+, but not by CD5-Lp-3+sIgM+ B cells from 6-month-old mice. We suggest that surface phenotypes of anti-DNA antibody producers change from CD5+Lp-3-sIgM+IL-5R+, CD5+Lp-3+sIgM+IL-6R+ and subsequently to CD5-Lp-3+sIgM-(sIgG+)IL-6R+ in NZB/W F1 mice with aging.

Differential expression of a CD45R epitope(6B2) on murine CD5+ B cells: Possible difference in the post-translational modification of CD45 molecules

Although murine peritoneal B cells were homogenously positive for an epitope Lp-2, coded for by the alternative exon 4 of the CD45 gene, they were heterogenous with respect to the expression of another CD45R epitope, 6B2, of unknown exon dependency. While the majority of 6B2-high peritoneal B cells was composed of CD5- B cells, those with low or negative 6B2 were CD5+ B cells. Both 6B2+ and 6B2- peritoneal B cells expressed mainly the same largest CD45R transcripts, with all three alternative exon (4, 5, and 6) sequences. Further, a CD5+ B lymphoma cell line, BCL-1, which was found to be Lp-2+6B2- also had the largest isoform of CD45R molecules with all three alternate structures. Although enzyme digestion studies suggested that the 6B2 epitope resides in protein, not in sugar structures, it is likely that a post-translational modification of CD45R molecules is responsible for the presence or absence of 6B2 epitope expression on peritoneal CD5+ B cells. This event may be related to the differential role of CD45R molecules in regulating lymphocyte function.

Peritoneal B cells regulate the numbers of allotype-matched pre-B and B cells in bone marrow

The mechanisms regulating growth and differentiation of B-cell precursors in adult bone marrow (BM) and/or selecting immunocompetent cells for peripheral export are poorly understood. We report here that small numbers of activated peritoneal B cells selectively suppress the numbers of small pre-B (B220+IgM-) and B (B220+IgM+) cells in BM, if transferred into syngeneic adult mice. No significant alterations are detected in other BM cell lineages or in peripheral lymphocytes of recipient mice. Both CD5+ and CD5- peritoneal B cells display this activity, but the same or higher numbers of similarly activated splenic B cells have no effect. Suppression of B-lineage cells is independent of T lymphocytes but requires that both donor and recipient are matched for immunoglobulin allotypes. These findings provide evidence for regulation of BM B-cell production by peripheral B cells, especially when located in the peritoneal cavity, and ascribe regulatory roles to the peritoneal B-cell compartment. They also could contribute to understanding the control of total B-lymphocyte numbers in the organism.

Major histocompatibility complex controls clonal proliferation of CD5+ B cells in H-2-congenic New Zealand mice: a model for B cell chronic lymphocytic leukemia and autoimmune disease

By employing H-2-congenic NZB, NZW and (NZB x NZW)F1 mice with either the homozygous H-2d/H-2d, H-2z/H-2z or heterozygous H-2d/H-2z haplotype, we found that in the spleen of all the congenic strains homozygous for H-2z, there were extremely high frequencies of CD5+ B cells. These cells eventually proliferated in an oligoclonal or even monoclonal fashion, and B cell-chronic lymphocytic leukemia (B-CLL) developed in some cases. Because this feature was not observed in H-2d/H-2d homozygotes or H-2d/H-2z heterozygotes, the high CD5+ B cell frequencies are apparently controlled by the homozygosity of a locus or cluster of loci closely linked to H-2z complex of NZW strain. As the CD5+ B cell frequencies in the peritoneal cavity did not differ among the H-2-congenic strains, the frequencies of these cells in the peritoneal cavity and in the spleen appear to be at least in part under separate control. Flow cytometry and Southern blot analyses using an immunoglobulin gene JH probe revealed that the H-2z/H-2z homozygotes, there was a propagation of distinct clonal populations between the spleen and the peritoneal cavity, a finding which suggested that in the major histocompatibility complex (MHC)-related microenvironments for CD5+ B cell propagation differ between the two compartments. All our findings taken together imply that certain different but related MHC haplotypes may predispose either to B-CLL or to autoimmune disease, in close relatives.

Biased VH gene expression in murine CD5 B cells results from age-dependent cellular selection

Flow cytometry-purified, peritoneal and splenic CD5+ and CD5- B cells from neonatal and adult C57BL/6 mice were studied for expression of VH and Vx gene families in RNA colony blot assays, and for frequencies of clones secreting antibodies to bromelain-treated mouse red blood cells (BrMRBC), single-stranded DNA, trimethyl ammonium and bovine gamma-globulin, by limiting dilution. The results show few overall differences between the two B cell subsets, which both manifest ontogenic D-proximal VH preferences that are lost with age. Biased VH11 expression in CD5 B cells is high in adult peritoneum and spleen but absent in newborns. It only partly correlates with the selection of anti-BrMRBC reactivity, which is considerably higher in peritoneum than in spleen. No particular Vx bias was observed in any of the populations studied with the possible exception of Vx22 in peritoneal CD5+ B cells. We conclude that the antibody repertoire expressed by peritoneal CD5+ B cells of adult mice is not the result of a genetic program, but rather the consequence of local, age-dependent cellular selection mechanisms.

Normal serum immunoglobulins influence the numbers of bone marrow pre-B and B cells

The homeostatic mechanisms controlling B lymphocyte output from bone marrow are not well understood. The present experiments evaluated putative influences of circulating immunoglobulins (Ig) on bone marrow (BM) pre-B and B cell populations. Injections into normal mice of Ig isolated from normal mouse serum, resulted in a dose-dependent and reversible reduction in numbers of BM B lineage cells, in particular of small B220+ surface IgM- cells. Maximal effects were observed upon injection of isologous polyclonal Ig and were independent of mature T cells. These results suggest a feedback modulation of peripheral Ig on cellular activities in BM B lineage compartments, mediated by mechanisms that seem to involve the variable regions of the Ig molecule.

Stimulation of B and T cells by in vivo high dose immunoglobulin administration in normal mice

Adult BALB/c mice were injected intravenously with a preparation of pooled normal murine IgG (400 mg/kg/day, on five consecutive days) and studied 8, 15, and 60 days later. High dose IgG administration increased the total numbers of splenic activated B and CD4+ (but not CD8+) T cells, as well as the numbers of splenic Ig-secreting cells, particularly in the IgG isotypes. Reactivities to some autoantigens, but not to bacterial or other heteroantigens, were selectively amplified amongst IgM-secreting cells. IgG administration did not alter the specific primary immune response to heterologous erythrocytes or bacterial dextran. No cellular alterations were detected in the lymph nodes or peritoneal cavity of treated animals. Most of these effects subsided with time, but some autoantibody reactivities remained elevated 60 days later. The present results suggest that the therapeutic effects of high dose IgG administration which have been reported in human diseases might be associated with the immunostimulatory activities of such treatment.

A mouse monoclonal antibody specific for an allotypic determinant of the Igha allele of murine IgM: genetic and functional analysis of Igh-6a epitopes using anti-IgM monoclonal antibodies

An IgG1 mouse monoclonal antibody (MAb) specific for a mouse IgM allotypic determinant in the a, c, f, g, h, and j haplotypes was derived from a fusion of SP2/O-Ag14 mouse myeloma cells with C57BL/6 mouse spleen cells (Igh-Cb) immune to TC31, a MAb of the IgMa allotype. MAb from one hybridoma derived from this fusion (designated DS1) was demonstrated to bind in an ELISA to immunoglobulin bearing the IgMa allotype (TC31, MOPC104E), but not to immunoglobulin bearing the IgMb allotype (C.BPC112). Fluorescein-conjugated DS1 was shown to bind to the surface of BALB/cByJ splenic B cells, but was shown to have negligible binding on C57BL/6J cells. Similarly, DS1-conjugated Sepharose beads were able to stimulate in vitro proliferation of BALB/c, but not C57BL/6 splenic B cells. DS1 was unable to bind to spleen cells from BALB/c allotype congenic strains, BAB/14 (Igh-Cb) and C.AL-20 (Igh-Co), demonstrating that DS1 recognizes a determinant under the control of a gene linked to the Igh-C gene complex. Using sera from recombinant inbred lines, the determinant defined by DS1 was shown to be linked to the Igh-1 locus. Furthermore, the determinant was localized to the CH1 domain of the mu heavy chain. Sera from BALB/cByJ, NMRI, CBA/J, SEA/GnJ, RIIIs/J, and CE/J mouse strains were shown to bind to DS1 in an ELISA, while sera from A/J, SJL/J, NZB/B1NJ, AKR/J, C57BL/6J, and C57BL/10SnJ mouse strains did not bind to DS1. From these data we propose that DS1 is reactive with specificity Igh-6.1, which was originally defined by an allotypic antiserum developed by Black et al. (Immunogenetics 7:213, 1978).

2-Hydroxyethylnitrosourea induction of B cell lymphoma in female Swiss mice

Groups of 30 adult Swiss mice of both sexes from the Eppley Institute breeding colony were treated with 37.5 or 75 mg 2-hydroxyethylnitrosourea (HENU)/l citrate buffer, given as drinking water on 4 days/week from 6-8 weeks of age for life. A third group of mice was untreated. Incidences of generalized B cell lymphoma (BCL) were 67% (males) and 87% (females) for the higher dose of the nitrosourea, 29% (males) and 79% (females) for the lower dose and 0% (males) and 7% (females) for the untreated mice. Tumor latencies were 23 weeks (high dose) and 27 weeks (low dose) in the females and 6-7 weeks longer in the males. A B-cell origin of the lymphomas was indicated by the pathology and tumor distribution and was confirmed in 4 mice by immunophenotyping and in 6 mice by probes for gene rearrangements. This system may be an effective means of inducing B cell lymphoma with a carcinogen.

Inside the thymus, Mls antigen is exclusively presented by B lymphocytes

The ability to stimulate an Mls-1 mixed lymphocyte reaction (MLR) is predominantly expressed by low density B lymphocytes in the spleen and peritoneal cavity of normal adult mice, and is absent in splenic B cells 1 month after lethal irradiation and reconstitution from autologous bone marrow. Coreconstitution of these mice with normal syngeneic peritoneal cells restores the stimulatory potential of splenic B cells, but sorted CD5+ or CD5- IgM+ lymphocytes from peritoneum are equally good stimulators, suggesting that functional Mls-1 expression may require long life spans and selection. Bone-marrow-reconstituted DBA/2 mice that fail to express Mls-1 antigens in the periphery nevertheless maintain T-cell receptor V beta 6 and 8.1 deletions among the newly formed T cells. These findings led us to directly investigate the Mls stimulatory ability of purified antigen-presenting cell populations inside the thymus. We report here that thymic B lymphocytes seem to represent the only intrathymic cell population able to stimulate Mls-1 MLR.

Immune deficiency due to high copy numbers of an Ak beta transgene

Because allelic polymorphism of the major histocompatibility complex class II antigens affects the immune response at several levels, we wished to characterize the contribution of a particular alpha or beta chain in vivo using transgenic mice. We have established and characterized 12 lines of H-2s/s mice carrying from 1 to 65 copies of an Ak beta transgene. The transgene was coexpressed with the endogenous allele in a tissue-specific manner, and Ak beta mRNA expression correlated well with transgene copy number. High copy number (extreme overexpression) of the transgene was associated with a variety of defects, including a significant reduction in Ia cell-surface expression, a severe decrease in B-cell number, abnormal extramedullary granulopoiesis, and an increased susceptibility to infection. In this paper we describe in detail the phenotype associated with high copy numbers of the Ak beta transgene. The defects we have observed may be relevant to similar phenomena seen in other transgenic mice. In addition, these mice have fortuitously provided a system in which to assess the effect of various levels of class II cell-surface expression in the thymus on selection of the T-cell repertoire.

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

Selective peripheral expansion and activation of B cells expressing endogenous immunoglobulin in mu-transgenic mice

Two different lines of C57BL/6 mice (IgHb) carrying complete rearranged mu chain genes from BALB/c (IgMa) were analyzed for the expression and secretion of endogenous as well as transgenic immunoglobulins at the level of single cells. Quantitation of B cells expressing endogenous IgMb by cytofluorometry, limiting dilution analyses of clonal precursors and secretory cell assays revealed a marked selective expansion, activation and terminal differentiation of those cells producing endogenous immunoglobulins. Thus, the very infrequent IgMb-bearing B cells produced in bone marrow of transgenic mice accumulate in spleen, where they are activated and account for roughly half of all natural immunoglobulin-secreting cells. These observations indicate that mu-transgenic mice are valuable in studies of the antibody repertoire selection operating in unprimed animals but their use could be misleading in the analyzing "monoclonal" immune system.

Development of B-lineage cells in the bone marrow of scid/scid mice following the introduction of functionally rearranged immunoglobulin transgenes

Mice homozygous for the mutation scid (scid mice) are severely immunodeficient and generally lack detectable numbers of pre-B, B, and T cells. This condition is believed to result from a defect in the mechanism responsible for rearrangement of immunoglobulin and T-cell receptor genes in developing B and T lymphocytes. To test this hypothesis and evaluate whether scid affects only the process of gene recombination, we introduced functionally rearranged immunoglobulin genes into the scid mouse genome. As scid mice appear to contain early lymphoid cells committed to the B lineage (pro-B cells), we asked whether the introduction of an IgM heavy-chain gene alone (mu-transgenic scid mice) or both IgM heavy- and kappa light-chain genes (mu kappa-transgenic scid mice) would allow further differentiation of scid pro-B cells into pre-B and B cells. We found that normal numbers of pre-B cells appeared in the bone marrow of mu-transgenic scid mice and that both pre-B and B cells appeared in the bone marrow of mu kappa-transgenic scid mice. However, in the latter case, the number of pre-B and B cells was 2- to 3-fold less than in the controls (mu kappa-transgenic scid heterozygotes) and few, if any, B cells were detectable in the peripheral lymphoid tissues. The implications of these results for the above hypothesis are discussed.

Distinct surface phenotypes of B cells responsible for spontaneous production of IgM and IgG anti-DNA antibodies in autoimmune-prone NZB x NZW F1 mice

Autoimmune-prone NZB x NZW F1 (B/W F1) mice produce a high titer of anti-DNA antibodies, In vivo and in vitro studies showed that in the early life of these mice, the immunoglobulin isotype of these antibodies almost exclusively belongs to IgM class, however, IgG anti-DNA antibodies begin to develop when the mice are about 5-6 months old and the titer exceeds that of IgM antibodies from age 7 months on. We asked whether or not the B cell population responsible for IgM and IgG antibody production belongs to the same lineage. The surface phenotypes of B cell populations responsible for the spontaneous production of either IgM or IgG anti-DNA antibodies were examined using panning and sorting methods with several monoclonal antibodies to B cells, including CD5 (Ly-1) and Lp-3; the latter defines a unique B cell differentiation antigen. We obtained evidence that surface phenotypes of B cells secreting IgM anti-DNA antibodies belong to CD5+ Lp-3- and those of B cells secreting IgG anti-DNA antibodies which occur only in old B/W F1 mice belong to CD5- Lp-3+ subpopulations. The majority of peritoneal B cells were CD5+ Lp-3+ throughout the life span of the mice and anti-DNA antibody production was never evidenced. These findings were discussed in relation to age-associated changes of B cell populations in the spleen of this strain of mice.

Further evidence for coelomic-associated B lymphocytes

Previous observations indicate that "CD5 B lymphocytes" are preferentially clustered in gut-related mesenchymal areas, such as peritoneum, thymus and tonsils. We have now found that pleuropericardial spaces contain an homogeneous population of large-sized, noncycling, nonsecretory B cells, expressing very high levels of surface IgM, little or no IgD, Mac-1 and low levels of B220. This phenotype and the over-representation of some antibody clonotypes suggest that the pleuropericardial cavity contains a pure "CD5 B cell" population. In all mouse strains analyzed, however, many of these cells are CD5-. These findings, together with the common origin of peritoneum and pleural layers in the primitive coelomic cavity, suggest that such B cells differentiate locally from intraembryonic precursors; we propose to designate them as "coelomic", to distinguish them from "stromal", bone marrow-derived B cells.

B lymphocytes express and lose syndecan at specific stages of differentiation

Lymphopoietic cells require interactions with bone marrow stroma for normal maturation and show changes in adhesion to matrix during their differentiation. Syndecan, a heparan sulfate-rich integral membrane proteoglycan, functions as a matrix receptor by binding cells to interstitial collagens, fibronectin, and thrombospondin. Therefore, we asked whether syndecan was present on the surface of lymphopoietic cells. In bone marrow, we find syndecan only on precursor B cells. Expression changes with pre-B cell maturation in the marrow and with B-lymphocyte differentiation to plasma cells in interstitial matrices. Syndecan on B cell precursors is more heterogeneous and slightly larger than on plasma cells. Syndecan 1) is lost immediately before maturation and release of B lymphocytes into the circulation, 2) is absent on circulating and peripheral B lymphocytes, and 3) is reexpressed upon their differentiation into immobilized plasma cells. Thus, syndecan is expressed only when and where B lymphocytes associate with extracellular matrix. These results indicate that B cells differentiating in vivo alter their matrix receptor expression and suggest a role for syndecan in B cell stage-specific adhesion.

Plasticity of T-cell function. II. Transient induction of CD8 (Ly-2) expression in cloned EL-4 lymphoma cells depending on cell density

EL-4 lymphoma cells are able to suppress the primary humoral immune response of spleen cells to sheep erythrocytes or 4-hydroxy-3-iodo-5-nitrophenylacetyl-keyhole limpet haemocyanin (NIP-KLH) in vitro. Typically, the cells suppress very efficiently in small numbers, but lose this capacity as the numbers increase. Three clones were analysed and this fluctuation in function was paralleled by a fluctuation in the expression of CD8 (Ly-2). Clones were incubated for 2 days, starting from different seeding concentrations, and analysed with cytofluorography. Neither Thy-1 nor CD5 (Ly-1), H-2 K, H-2 D, LFA-1 (all positive) nor CD4 (L3T4) or MEL-14 (both negative) were influenced by this treatment. In contrast, cells were CD8- at high seeding concentrations, and CD8+ at low seeding concentrations. When cell cultures grew to higher densities, the cells again lost the capacity to express CD8. Experiments testing the suppressive capacity of individual EL-4 clones after preculture at different densities or in the presence of antibodies against CD8 suggest that the efficiency of suppression may well be correlated to the amount of CD8 expressed.

Ontogenic development of autoantibody repertoires in spleen and peritoneal cavity of normal mice: examples of T cell-dependent and -independent reactivities

The ontogenic development of B cell clonal precursors (BCP) reactive to bromelain-treated, syngeneic erythrocytes (BrMRC) and to single-stranded DNA has been studied by limiting dilution of both spleen and peritoneal cells. It was found that the frequency of anti-BrMRC BCP in the spleen is very low up to 4 weeks of age and slowly increases thereafter, to reach adult levels by 6-10 weeks. In the peritoneal cavity, no such BCP can be found before 2 weeks, but they occur at a very high frequency already by 3 weeks of age. Injection of adult, normal syngeneic T cells at birth has no apparent effect on the representation of anti-BrMRC BCP in the peritoneal cavity, but brings these to adult levels or even higher in the spleen already at 3 weeks of age. Accordingly, adult athymic (nude) mice contain normal frequencies of BrMRC-specific BCP in the peritoneal cavity but are devoid of such clones in the spleen. In contrast, the frequency of anti-DNA BCP is very high throughout postnatal development in both spleen and peritoneal cavity, of normal and athymic mice, in both resting and naturally activated splenic B cell compartments, and it is independent of T cell transfers into nude animals. These results indicate the role of T cells in the establishment of some clonal specificities in the adult, splenic autoreactive B cell repertoire.

Immunoglobulin VH gene expression in Ly-1+ and conventional B lymphocytes

Lymphocyte populations in which Ly-1 B cells are differentially represented were studied for the expression of ten VH gene families, either by an RNA colony blot assay or by in situ hybridization of single cells, in BALB/c and C57BL/6 mice. The comparisons of cells from lymph nodes, Peyer's patches and adult spleen (poor in Ly-1 B cells) with cells from peritoneal cavity and neonatal spleen (rich in Ly-1 B cells) were confirmed by the analysis of adult peritoneal Ly-1- and Ly-1+ B cells sorted on the fluorescence-activated cell sorter. The results indicate that the peritoneal Ly-1+ B subset uses the whole spectrum of known VH gene families, and shows a preferential utilization of CP12 VH genes, most likely as a result of a selective process during life.

Permanent alteration of the murine Ly-1 B repertoire due to selective depletion of Ly-1 B cells in neonatal animals

Studies presented here demonstrate that paternal allotype Ly-1 B cells are permanently depleted following neonatal treatment with antibodies to the paternal IgM allotype. Paternal allotype conventional B cells, in contrast, are temporarily depleted by treatment with either anti-IgM or anti-IgD allotype antibodies and return rapidly to normal frequencies once the antibody treatment disappears. These differences are explained by basic developmental differences between Ly-1 B and conventional lineage B cells. That is, the conventional B cell population is replenished from Ig- precursors throughout life and, therefore, is only temporarily affected when depleted in neonates. The Ly-1 B cell population, in contrast, develops from Ig- progenitors during the prenatal and neonatal life but survives because it is exclusively self-replenishing in adults. Therefore, elimination of a population of Ly-1 B cells from neonates is tantamount to removing it forever. These findings suggest that while conventional B cells turn over rapidly and have an effectively unlimited repertoire, Ly-1 B cells express a repertoire whose composition is strongly influenced by neonatal conditions that favor or select against the retention of cells producing certain antibody molecules. Thus, Ly-1 B cells play a unique role in the immune system in that they retain indefinitely the history of the neonatal animal's immunological experience.

Immune status of a mu, kappa transgenic mouse line. Deficient response to bacterially related antigens

We have examined the immune repertoire and immune response of a mouse that carries transgenes for a mu heavy chain and kappa light chain. The expression of these genes is under the regulation of their own controlling elements. The transgenes are expressed early in ontogeny and are easily detectable from day 13 of gestation onwards. The pre-B cells seem to function normally as they generate IgM-secreting colonies at normal frequencies. Colonies show predominantly the transgenic specificity. Expression of the transgenes is not limited to B cells since around 10%-20% of peripheral T cells and 50% of thymocytes express the mu transgene as an intracellular protein. Ectopic expression of kappa was not seen. The spleen size of the transgenic mouse is decreased by around 20%; this reduction is largely caused by a reduction of the B cell pool. Almost all B cells express the transgenes, only 30% co-express endogenous heavy chain genes and all co-express endogenous light chain genes. Serum Ig levels for IgM and IgA were normal, 20% of the IgM consist of the transgenic product. Serum IgG levels were decreased. T cell functions (helper and cytotoxic) were normal. Immune responses to conventional antigens were impaired, especially in the early phases of the immune response, but after boosting they were virtually normal, except for IgG3 which remained low. Primary antibody responses to T cell-independent antigens of the class II type (bacterially related antigens) were absent, although precursor frequencies for these antigens were within the expected range. The significance of this finding, as it relates to allelic exclusion of Ig genes, is discussed.

A major peritoneal reservoir of precursors for intestinal IgA plasma cells

Studies presented examine the origin of IgA plasma cells in B lineage chimeric mice constructed by reconstituting lethally irradiated mice with a mixture of syngeneic bone marrow cells and peritoneal cells from Ig heavy chain allotype congenic donors. In these mice, essentially all B cells in spleen and Peyer's patches are derived from the bone marrow donor; however Ly-1 B lineage cells which have been mainly detected in the peritoneum are derived from the peritoneal cell donor. Surprisingly, roughly half of the IgA plasma cells in the lamina propria of the gut are also derived from the peritoneal cell donor, suggesting an important role for peritoneally-derived B cells in the mucosal immune response.

Prevention and reversal of experimental autoimmune thyroiditis (EAT) in mice by administration of anti-L3T4 monoclonal antibody at different stages of disease development

Experimental autoimmune thyroiditis (EAT) can be induced in CBA/J mice following the transfer of spleen cells from mouse thyroglobulin (MTg)-sensitized donors that have been activated in vitro with MTg. Since L3T4+ T cells are required to transfer EAT in this model, the present study was undertaken to assess the effectiveness of the anti-L3T4 monoclonal antibody (mAb) GK1.5 in preventing or arresting the development of EAT. Spleen cells from mice given mAb GK1.5 prior to sensitization with MTg and adjuvant could not transfer EAT to normal recipients and cells from these mice did not proliferate in vitro to MTg. Donor mice given GK1.5 before immunization did not develop anti-MTg autoantibody and recipients of cells from such mice also produced little anti-MTg. GK1.5 could also prevent the proliferation and activation of sensitized effector cell precursors when added to in vitro cultures. When a single injection of mAb GK1.5 was given to recipients of in vitro-activated spleen cells, EAT was reduced whether the mAb was given prior to cell transfer or as late as 19 days after cell transfer. Whereas the incidence and severity of EAT was consistently reduced by injecting recipient mice with GK1.5, the same mice generally had no reduction in anti-MTg autoantibody. Since EAT is consistently induced in control recipients by 14-19 days after cell transfer, the ability of mAb GK1.5 to inhibit EAT when injected 14 or 19 days after cell transfer indicates that a single injection of the mAb GK1.5 can cause reversal of the histopathologic lesions of EAT in mice. These studies further establish the important role of L3T4+ T cells in the pathogenesis of EAT in mice and also suggest that therapy with an appropriate mAb may be an effective treatment for certain autoimmune diseases even when the therapy is initiated late in the course of the disease.

Neuronal cell killing by the envelope protein of HIV and its prevention by vasoactive intestinal peptide

The clinical manifestations of AIDS (acquired immune deficiency syndrome) often include neuropsychiatric and neurological deficits, including early memory loss and progressive dementia. HIV (human immunodeficiency virus), the aetiological agent of AIDS, is probably carried by infected macrophages in the central nervous system. The virus enters cells by binding its envelope glycoprotein gp120 to the CD4 antigen present on brain and immune cells. From the data reported in this paper, we now suggest that the neuronal deficits associated with HIV may not be entirely a result of infectivity, but that gp120 shed from HIV could directly produce the neuropathology as a result of its interference with endogenous neurotrophic substances. It is known that an analogue of a sequence contained in vasoactive intestinal peptide (VIP) occurs in all known sequenced gp120 isolates and that VIP is important for neuronal survival in cell culture. Here we show that purified gp120 from two diverse HIV isolates and a recombinant gp120 from a third isolate were all potent in specifically producing significant neuronal cell death in dissociated hippocampal cultures derived from fetal mice, and that this could be reduced by monoclonal antibodies against the murine CD4 antigen and completely antagonized by VIP.

Feedback inhibition of immunoglobulin gene rearrangement by membrane mu, but not by secreted mu heavy chains

Previous work (6-10) has shown that allelic exclusion of Ig gene expression is controlled by functionally rearranged mu and kappa genes. This report deals with the comparison of membrane mu (micron) and secreted mu (microsecond) in promoting such feedback inhibition. Splenic B cell hybridomas were analyzed from transgenic mice harboring a rearranged kappa gene alone or in combination with either an intact rearranged mu gene or a truncated version of the mu gene. The intact mu gene is capable of producing both membrane and secreted forms of the protein, while the truncated version can only encode the secreted form. The role of the microsecond was also tested in pre-B cell lines. Analysis of the extent of endogenous Ig gene rearrangement revealed that (a) the production of micron together with kappa can terminate Ig gene rearrangement; (b) microsecond with kappa does not have this feedback effect; (c) microsecond may interfere with the effect of micron and kappa; and (d) the feedback shown here probably represents a complete shutoff of the specific recombinase by micron + kappa; the data do not address the question of mu alone affecting the accessibility of H genes for rearrangement.

Normal mouse peritoneum contains a large population of Ly-1+ (CD5) B cells that recognize phosphatidyl choline. Relationship to cells that secrete hemolytic antibody specific for autologous erythrocytes

We have found that, in the peritoneums of normal adult mice, 5-15% of lymphocytes bind a fluorescent liposome probe. In ontogeny, cells with this specificity were shown to appear by 8 d after birth, and increase to the adult frequency by 2-3 wk. Some older mice contain an expanded population of these cells. We have shown that liposome binding occurs by cell surface IgM recognizing the common membrane phospholipid, phosphatidyl choline (PtC). Virtually all of these PtC-specific cells bear the cell surface marker Ly-1. Our results indicate that roughly 1 in 10 peritoneal Ly-1+ B cells has this single specificity. We have found that the precursors to all the cells that form plaques on protease-treated autologous erythrocytes (BrMRBC) are included in the PtC-specific population and can be isolated by FACS. We believe this is the first report of sorting large numbers of B cells with a single antigen specificity from normal, unimmunized animals. This method will allow for in vitro and in vivo studies of differentiative and proliferative properties of Ly-1+ B cells, which may help define their role in development and disease.

Characterization of proximal colonic lymphoid tissue in the mouse

Here we describe a nodule of lymphoid tissue which was consistently located in the proximal colon of mice approximately 25% of the distance from the cecum to the rectum. Immunohistochemical characterization of this nodule demonstrated that the majority of lymphocytes were relatively immature 14.8+ (B220+), IgM+, Ia+ (specificity 20) B cells some of which were also Ly-1+. These nodules also possessed an occasional T cell (Thy-1+, Ly-1+, Lyt-2+) aggregate at the periphery. Rare, small areas did not stain for either T or B cell markers. These lymphoid nodules were associated with epithelial cells which stained positively with the ER-TR4 monoclonal antibody (which also recognizes thymic cortical epithelial cells) and also with ER-TR6, which has been reported to recognize thymic macrophages or dendritic cells. The overlying colonic epithelium stained intensely with the ER-TR4 monoclonal antibody. Proximal colonic lymphoid tissue was extremely sensitive to steroid treatment, losing approximately 80% of its mass within 24 hours in response to a single intraperitoneal injection of 2 mg hydrocortisone acetate. This response was similar to that of the thymus and to that reported for the bursa of Fabricius, but unlike that of other gastrointestinal lymphoid aggregates. These results indicated that proximal colonic lymphoid tissue contains a high frequency of relatively immature B cells and may be a primary site of their generation, possibly including some of the Ly-1+ phenotype. These observations correlate with new evidence suggesting that the allantois participates in the formation of the distal midgut, including its lymphoid components.

Increased expression of major histocompatibility complex antigens on lymphocytes from aged mice

Many studies have reported age-related changes in immune responses that could be due to alterations in lymphoid cell numbers or functions. Here we report the results of studies using immunofluorescent staining and in vitro assays of cellular function to compare the expression of cell surface antigens on lymphocytes from mice up to 2 years of age. No significant changes were observed in the frequencies of spleen cells bearing class I or class II major histocompatibility complex (MHC) antigens, surface immunoglobulin, or Thy-1, Ly-1, Ly-2, or L3T4 antigens. However, the densities (per cell) of both class I and class II MHC antigens were increased significantly on cells from aged as compared to young mice, whereas the densities of the other cell surface antigens studied were unchanged or slightly decreased. The increased levels of MHC antigen expression in old relative to young mice were shown to be functionally significant regarding immunological stimulation. These data suggest that T-cell clones silent in young individuals may be activated in comparable situations in older animals, leading to immunological alterations perhaps including increased autoreactivity.

Study of the DBA/2Ha immunodeficiency: X-chromosome mosaicism and in vivo immunoresponses

DBA/2Ha mice have an X-chromosome-linked immunodeficiency and lack the receptor to a TRF (T cell replacing factor) on a subpopulation of B cells. Their immunodeficiency is considered to resemble that of CBA/N, another X-chromosome-linked immunodeficiency. To facilitate direct comparisons of the two immunodeficiencies and to study the in vivo manifestations of DBA/2Ha immunodeficiency, we measured phenotypes and functions of B cells of DBA/2Ha mice. We found that the expression of sIgM among B cells is normal in DBA/2Ha mice, heterozygous females equally express both affected and normal B cell subpopulations, and DBA/2Ha mice respond well to a TI-2 antigen (TNP-Ficoll) and a polyclonal activator (LPS). Unlike CBA/N, DBA/2Ha mice demonstrate very little in vivo immunodeficiencies.

Characterization of monoclonal antibodies that recognize band 4.5 polypeptides associated with nucleoside transport in pig erythrocytes

Three monoclonal antibodies have been raised against partially purified band 4.5 polypeptides [Steck (1974) J. Cell Biol. 62, 1-19] from pig erythrocyte membranes. The antibodies were capable of binding to both intact pig erythrocytes and protein-depleted membrane preparations and recognized detergent-solubilized polypeptides from adult and neonatal pig erythrocytes that were photolabelled with [G-3H]nitrobenzylthioinosine (NBMPR), a potent specific inhibitor of nucleoside transport. The antibodies did not recognize polypeptides from neonatal pig erythrocytes that were photolabelled with the glucose-transport inhibitor [3H]cytochalasin B. Reactivity with polypeptides of apparent Mr 64,000 [10% (w/v) acrylamide gels] was demonstrated by Western-blot analysis. The antibodies recognized pig band 4.5 polypeptides after prolonged treatment with endoglycosidase F, a finding consistent with reactivity against polypeptide, rather than carbohydrate, determinants. Trypsin digestion of NBMPR-labelled protein-depleted pig erythrocyte membranes generated two labelled polypeptide fragments (Mr 43,000 and 26,000). Two of the antibodies recognized both fragments on Western blots, whereas the third bound to the larger, but not to the smaller, fragment. The antibodies had no significant effect on reversible binding of NBMPR to protein-depleted pig erythrocyte membranes and did not bind to NBMPR-labelled polypeptides in human, rabbit or mouse erythrocytes.

Isolation of high-affinity memory B cells: phycoerythrin as a probe for antigen-binding cells

In multiparameter fluorescence-activated cell sorter studies presented here, we use the highly fluorescent protein phycoerythrin (PE) as an immunizing antigen and as a fluorescent probe to reveal and isolate antigen-binding memory B cells. We demonstrate directly that memory B cells in spleens from PE-primed mice stain brightly with PE and produce strong IgG1 anti-PE responses when sorted and cultured with L3T4+ helper T cells. That is, as few as 500 sorted PE-binding cells per culture well are sufficient to produce high-level anti-PE responses, presenting antigen in a form that induces helper T cells. Three-color immunofluorescence studies reveal that cells staining brightly with PE reside primarily in a population of B220+(IgM,IgD)- cells and comprise 0.02-0.05% of the spleen cells. Complementary studies with 2,4-dinitrophenyl memory B cells show that whereas this B220+-(IgM,IgD)- population (which comprises only 1-2% of the spleen cells) gives high-affinity anti-dinitrophenyl responses, the predominant B220+(IgM,IgD)+ population yields only low-affinity antibody. Finally, we find that although both populations have similar Ia levels, cells in the high-affinity fraction have greatly reduced levels of surface immunoglobulin.

The kinetic study on cell surface antigens of a hybridoma between human B cells and a mouse B-cell line

Human B cells obtained from tonsils were fused with a mutant clone of a murine B-cell line in the presence of polyethylene glycol and dimethyl sulfoxide. THT12.58, a subclone of the human-mouse B-cell hybridoma, was shown to express human B-cell surface antigens on the cell membrane, namely B1, B2, I2, human IgM and IgD derived from human B cells by analysis of flow microfluorometry (FMF), as well as murine B-cell markers; the amount of these human B-cell markers on THT12.58 did not change for more than 1 year after establishment. Interestingly, the expression of the human B-cell antigens significantly decreased after treatment of the cells with B-cell stimulatory factors (BSF) obtained from the supernatant of the culture of PHA-P activated T cells; this was followed by significant enlargement in cell size compared with the control. A marked decrease in the amount of each antigen on the hybrid was observed when treated with Staphylococcus aureus Cowan I strain (SAC) in addition to BSF. In contrast, the expression of these markers on the cells increased after exposure of the cells to recombinant human interferon-gamma (rINF-gamma). Additionally, the effect of BSF on the generation of IgM-secreting cells by human B cells markedly decreased after absorption of BSF with the hybrid cells. These results suggest that THT12.58 may possess a receptor for BSF on the cell surface, and be capable of differentiating into much more mature stage of B-cell lineage after exposure to BSF. Thus, this kind of a human-mouse B-cell hybridoma with human B-cell differentiation antigens can be a good model to investigate the kinetics of cell surface antigens and characterization of a receptor for BSF on human B cells.