The immunodominant antibody response to Zika virus NS1 protein is characterized by cross-reactivity to self

Besides antigen-specific responses to viral antigens, humoral immune response in virus infection can generate polyreactive and autoreactive antibodies. Dengue and Zika virus infections have been linked to antibody-mediated autoimmune disorders, including Guillain-Barré syndrome. A unique feature of flaviviruses is the secretion of nonstructural protein 1 (NS1) by infected cells. NS1 is highly immunogenic, and antibodies targeting NS1 can have both protective and pathogenic roles. In the present study, we investigated the humoral immune response to Zika virus NS1 and found NS1 to be an immunodominant viral antigen associated with the presence of autoreactive antibodies. Through single B cell cultures, we coupled binding assays and BCR sequencing, confirming the immunodominance of NS1. We demonstrate the presence of self-reactive clones in germinal centers after both infection and immunization, some of which present cross-reactivity with NS1. Sequence analysis of anti-NS1 B cell clones showed sequence features associated with pathogenic autoreactive antibodies. Our findings demonstrate NS1 immunodominance at the cellular level as well as a potential role for NS1 in ZIKV-associated autoimmune manifestations.

TLR9 Signaling Suppresses the Canonical Plasma Cell Differentiation Program in Follicular B Cells

The relative potency and quality of mouse B cell response to Toll-like receptors (TLRs) signaling varies significantly depending on the B cell subset and on the TLR member being engaged. Although it has been shown that marginal zone cells respond faster than follicular (FO) splenic B cells to TLR4 stimulus, FO B cells retain full capacity to proliferate and generate plasmablasts and plasma cells (PBs/PCs) with 2–3 days delayed kinetics. It is not clear whether this scenario could be extended to other members of the TLR family. Here, using quantitative cell culture conditions optimized for B cell growth and differentiation, we show that TLR9 signaling by CpG, while promoting vigorous proliferation, completely fails to induce differentiation of FO B cells into PBs/PCs. Little or absent Ig secretion following TLR9 stimulus was accompanied by lack of expression of cell surface markers and canonical transcription factors involved in PB/PC differentiation. Moreover, not only TLR9 did not induce plasmocyte differentiation, but it also strongly inhibited the massive PB/PC differentiation of FO B cells triggered by LPS/TLR4. Our study reveals unexpected opposite roles for TLR4 and TLR9 in the control of plasma cell differentiation program and disagrees with previous conclusions obtained in high-density cultures conditions on the generation of plasmocytes by TRL9 signaling. The potential implications of these findings on the role of TLR9 in controlling self-tolerance, clonal sizes and regulation of humoral responses are discussed.

The Global Self-Reactivity Profile of the Natural Antibody Repertoire Is Largely Independent of Germline DH Sequence

Natural antibodies (NAbs) are produced in the absence of exogenous antigenic stimulation and circulate in the blood of normal, healthy individuals. These antibodies have been shown to provide one of the first lines of defense against both bacterial and viral pathogens. Conservation of the NAb repertoire reactivity profile is observed both within and across species. One view holds that this conservation of NAb self-reactivities reflects the use of germline antibody sequence, whereas the opposing view holds that the self-reactivities reflect selection driven by key conserved self-antigens. In mice, B-1a B cells are a major source of NAbs. A significant fraction of the B-1a antibody repertoire is devoid of N nucleotides in H chain complementarity determining region 3 (CDR-H3) and, thus, completely germline encoded. To test the role of germline D_H sequence on the self-reactivity profile of the NAb repertoire, we examined the composition and self-antigen specificity of NAbs produced by a panel of D_H gene-targeted BALB/c mice, each strain of which expresses a polyclonal, altered CDR-H3 repertoire that differs from the wild-type norm. We found that in most cases the same key self-antigens were recognized by the NAbs created by each D_H-altered strain. The differences in reactivity appeared to represent the genetic signature of the NAb repertoire of each mouse strain. These findings suggest that although germline CDR-H3 sequence may facilitate the production of certain NAbs, a core set of self-antigens are likely the main force driving the selection of Nab self-specificities.

Abstract B39: Neutrophils G-CSF stimulated promotes specific protection against graft vs. host disease and keeps the graft vs. leukemia effect

Allogeneic hematopoietic stem cell transplantation (HSCT) is used to treat a series of hematological diseases. While the presence of T cells mediates the graft-versus-leukemia (GVL) effect and improves engraftment, it is also responsible for the graft-versus-host disease (GVHD), which is the main barrier of HSCT. Patients transplanted with cells from G-CSF treated donors show an unexpected low rate of acute GVHD given the high numbers of T cells present. We have previously shown that blood from G-CSF treated donors have high numbers of inhibitory granulocytes. Experimentally these granulocytes are able to prevent aGVHD in a semi-allogeneic mouse model. Here, our goal is to characterize the granulocytes and its mechanism of action. When we compare this granulocytes from the spleens of 5 day G-CSF treated donors and its untreated control, we observed on flow cytometry that the percentage of this granulocytes/neutrophils Ly6G+ increases from about 2% to about 20%. These cells have some differences among themselves after treatment as increased burst oxidative (measured by DHR) and phagocytosis of E.coli, as well as differences in the pattern of expression of some important surface molecules, such as MHC-II. Levels of myeloperoxidase are lower after treatment with G-CSF, and we confirmed by transmission electron microscopy that these neutrophils have a degranulated profile, with 83% fewer cytoplasmic granules than controls. Indeed, the spleens from 5 day G-CSF treated donors together with control bone marrow cells (G-B6) injected into irradiated F1(B6XBALB/c) mice shows survival rate of 100%, against 10% in non-G-B6 transplants. This protection depends on Gr1+ cells and presents milder pathological and clinical manifestations in gastrointestinal mucosa, skin and liver. However, when these G-B6 neutrophils are from IL-10 KO mice, protection is abolished both in survival curve and in clinical score. Surprisingly, 25 days after transplantation the percentage of the subtype of T regulatory Foxp3+ cells in protected chimeras is increased in all lymphoid organs analyzed and this can be associated with the long term specific tolerance observed. Finally, the anti-tumoral effect in G-B6 chimeras is as potent as in the B6 control chimera and this effect was maintained for more than 20 weeks after HSCT. So we can conclude that treatment with G-CSF generates degranulated neutrophils that reduce GVHD in an IL-10 dependent manner while keeping GVL effect opening a promising road in the prevention of human aGVHD. Financial Support: FAF, INCA, Swiss Bridge, INCT Cancer, FAPERJ, CNPQ, CAPES, Fiocruz.

Citation Format: Suelen Martins Perobelli, Ana Carolina Terra Mercadante, Triciana Gonçalves-Silva, Rômulo Galvani, Antônio Pereira-Neves, Marlene Benchimol, Alberto Nobrega, Adriana Bonomo. Neutrophils G-CSF stimulated promotes specific protection against graft vs. host disease and keeps the graft vs. leukemia effect. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B39.

The role of evolutionarily conserved germ-line DH sequence in B-1 cell development and natural antibody production

Because of N addition and variation in the site of VDJ joining, the third complementarity-determining region of the heavy chain (CDR-H3) is the most diverse component of the initial immunoglobulin antigen-binding site repertoire. A large component of the peritoneal cavity B-1 cell component is the product of fetal and perinatal B cell production. The CDR-H3 repertoire is thus depleted of N addition, which increases dependency on germ-line sequence. Cross-species comparisons have shown that DH gene sequence demonstrates conservation of amino acid preferences by reading frame. Preference for reading frame 1, which is enriched for tyrosine and glycine, is created both by rearrangement patterns and by pre-BCR and BCR selection. In previous studies, we have assessed the role of conserved DH sequence by examining peritoneal cavity B-1 cell numbers and antibody production in BALB/c mice with altered DH loci. Here, we review our finding that changes in the constraints normally imposed by germ-line-encoded amino acids within the CDR-H3 repertoire profoundly affect B-1 cell development, especially B-1a cells, and thus natural antibody immunity. Our studies suggest that both natural and somatic selection operate to create a restricted B-1 cell CDR-H3 repertoire.

The link between antibodies to OxLDL and natural protection against pneumococci depends on D(H) gene conservation

Germline D_H sequences are required for the generation of natural antibodies reactive to bacterial phosphorylcholine but not for those reactive to self-antigen.

Selection and physiological production of protective natural antibodies (NAbs) have been associated with exposure to endogenous antigens. The extent to which this association depends on germline NAb sequence is uncertain. Here we show that alterations in germline D_H sequence can sever the association between the production of self-reactive NAbs and NAbs that afford protection against a pathogen. In unmanipulated hosts, the availability of the evolutionarily conserved DFL16.1 gene segment sequence profoundly affected the serum levels of NAbs against bacterial phosphorylcholine but not oxidized low-density lipoprotein. Mice with partially altered DFL16.1 sequence could use N nucleotides to recreate the amino acid sequence associated with the classical protective T15 idiotype–positive NAbs, whereas those without DFL16.1 could not. DFL16.1 gene–deficient mice proved more susceptible to challenge with live Streptococcus pneumoniae. Our findings indicate that although production of self-reactive NAbs can be independent of germline D_H sequence, their capacity to provide protection against pathogens cannot. The potential relevance of these findings for the rational design of vaccines is discussed.

A rapid and quantitative method for the evaluation of V gene usage, specificities and the clonal size of B cell repertoires

The quantitative simultaneous description of both variable region gene usage and antigen specificity of immunoglobulin repertoires is a major goal in immunology. Current quantitative assays are labor intensive and depend on extensive gene expression cloning prior to screening for antigen specificity. Here we describe an alternative method based on high efficiency single B cell cultures coupled with RT-PCR that can be used for rapid characterization of immunoglobulin gene segment usage, clonal size and antigen specificity. This simplified approach should facilitate the study of antibody repertoires expressed by defined B cell subpopulations, the analysis of immune responses to self and nonself-antigens, the development and screening of synthetic antibodies and the accelerated study and screening of neutralizing antibodies to pathogenic threats.

Modulation of mature B cells in mice following treatment with ouabain

Ouabain (OUA) is an endogenous hormone released by the adrenal gland under stress situations. Steroid hormones and glucocorticoids have been characterized as selective inhibitors of lymphopoiesis. The present report shows in vivo modulation of mature B cells in bone marrow, spleen and peripheral blood by ouabain. Mice injected intraperitonially (i.p.) with ouabain 0.56 mg/kg for 3 consecutive days displayed, 24 h after last injection, a decreased cellularity in the bone marrow with diminution of the mature B cell subpopulation while the other B cell subpopulations were preserved. Percentually, the myeloid lineage in bone marrow was increased by ouabain. Numbers of mature B lymphocytes in spleen and peripheral blood were reduced following in vivo treatment. In vitro, the B cell populations were not affected. The effects appear to be independent of steroid hormones and strain. The presence of stable levels of glucocorticoids seems to be important because the effects could only be observed from the fourth week animal's life, when glucocorticoid levels are stable. These results open new perspectives for a potential use of ouabain as an immunomodulator.

TLR4 promotes B cell maturation: independence and cooperation with B lymphocyte-activating factor

We have previously shown that TLR4 triggering promotes the generation of CD23(+)CD93(+) transitional T2-like cells in vitro from mouse B cell precursors, suggesting a possible role for this receptor in B cell maturation. In this study, we perform an extensive study of cell surface markers and functional properties of B cells matured in vitro with LPS, comparatively with the well-known B cell maturation factor B lymphocyte-activating factor (BAFF). LPS increased generation of CD23(+) transitional B cells in a TLR4-dependent way, upregulating IgD and CD21 and downregulating CD93, without inducing cell proliferation, in a manner essentially equivalent to BAFF. For both BAFF and LPS, functional maturation of the IgM(+)CD23(+)CD93(+) cells was confirmed by their higher proliferative response to anti-CD40 plus IL-4 compared with IgM(+)CD23(neg)CD93(+) cells. BAFF-R-Fc-mediated neutralization experiments showed that TLR4-induced B cell maturation was independent of BAFF. Distinct from BAFF, maturation by LPS relied on the activation of canonical NF-kappaB pathway, and the two factors together had complementary effects, leading to higher numbers of IgM(+)CD23(+)CD93(+) cells with their simultaneous addition. Importantly, BCR cross-linking abrogated the generation of CD23(+) B cells by LPS or BAFF, indicating that signals mimicking central tolerance act on both systems. Addition of cyclosporin A reverted BCR-mediated inhibition, both for BAFF and LPS, suggesting similar regulation of signaling pathways by calcineurin. Finally, LPS-injected mice showed a rapid increase of mature B cells in the bone marrow, suggesting that TLR4 signaling may effectively stimulate B cell maturation in vivo, acting as an accessory stimulus in B cell development, complementary to the BAFF physiological pathway.

Innate profiles of cytokines implicated on oral tolerance correlate with low- or high-suppression of humoral response

SUMMARY

Oral tolerance (OT) is being studied with great interest because of its therapeutic potential in allergy and autoimmunity. In the present study, two mouse strains with extreme phenotypes of OT susceptibility (TS) or resistance (TR) to ovalbumin (OVA) were used to demonstrate whether the tr and ts genes, cumulated during 18 generations of bi-directional genetic selection, influence expression of immunobiological traits in naive or antigen-gavaged TR/TS mice. The difference in anti-OVA titres was 2048-fold between OVA-gavaged TS and TR mice. Tolerance susceptibility to OVA gavage in individuals from a (TS x TR)F(2) population was 24% high-susceptibility, 62% low-susceptibility and 14% non-tolerant. Different antigens, unrelated to OVA, were tested by gavage and TS mice were generally susceptible while TR mice were resistant. The stability of TS and TR phenotypes was not affected by the use of strict protocols of intraperitoneal immunization or feeding over 30 consecutive days. The levels of interleukin-2 (IL-2), IL-4, interferon-gamma and IL-10 cytokines evaluated in concanavalin A-stimulated spleen cells from naive mice and in OVA-stimulated spleen cells from OVA-gavaged mice were higher in TS mice. Interleukin-10 was up-regulated in OVA-gavaged TS mice and down-regulated in TR mice. In naive mice, the percentage of CD4(+) CD25(+) and CD4(+) Foxp3(+) spleen cells and IL-10 expression by CD4(+) cells was significantly higher in TS mice. These results indicate that regulation of IL-10 expression could be an important factor contributing to the mechanisms controlling OT susceptibility, and that the OT responses of TR and TS individuals strongly correlate with their innate potential to secrete this cytokine.

Genetic control of the B cell response to LPS: opposing effects in peritoneal versus splenic B cell populations

Lipopolysaccharide (LPS) from gram-negative bacteria activates B cells, enabling them to proliferate and differentiate into plasma cells. This response is critically dependent on the expression of TLR4; but other genes, such as RP105 and MHC class II, have also been shown to contribute to B cell LPS response. Here, we have evaluated the role of genetic control of the B cell response to LPS at the single cell level. We compared the response to LPS of peritoneal cavity (PEC) and splenic B cells on the BALB/c genetic background (LPS-low responder) to those on the C57BL/6J background (LPS-high responder) and their F1 progeny (CB6F1). Both PEC and splenic B cells from B6 exhibited 100% clonal growth in the presence of LPS; whereas, BALB/c PEC and splenic B cells achieved only 50% and 23% clonal growth, respectively. Adding CpG to the LPS stimulus pushed PEC B cell clonal growth in the low responder strain BALB/c up to 90%, showing that the nonresponse to LPS is a specific effect. Surprisingly, PEC B cells on the F1 background behaved as high responders, while splenic B cells behaved as low responders to LPS. The data presented here reveals a previous unsuspected behavior in the genetic control of the B cell response to LPS with an opposing impact in splenic versus peritoneal cavity B cells. These results suggest the existence of an, as yet, unidentified genetic factor exclusively expressed by coelomic B cells that contributes to the control of the LPS signaling pathway in the B lymphocyte.

Inhibition of B cell development by kalanchosine dimalate

Kalanchoe brasiliensis (Kb) is a medicinal plant from the Crassulaceae family, used in folk medicine to treat inflammatory and infectious diseases. Here we show that short-term treatment of mice with a highly purified compound named kalanchosine dimalate (KMC), obtained from Kb, led to a strong and selective inhibition of B cell development in the bone marrow, without affecting the myeloid lineage development. Numbers of mature B lymphocytes in bone marrow or peripheral lymphoid organs were preserved in KMC treated mice. The inhibitory effect of KMC was acute and rapidly reverted with the interruption of the treatment. In vitro, KMC, inhibited the interleukin-7 dependent proliferation of B cell precursors and do not induce cell death. Also in vitro, the maturation of B cell precursors was not affected by KMC. KMC does not inhibit the proliferative response to IL-3 or IL-2. These results suggest that KMC is selectively affecting B cell lymphopoiesis, possibly acting on the IL-7 signaling pathway, opening new perspectives for a potential therapeutic usage of Kb derived drugs.

Selective blockade of lymphopoiesis induced by kalanchosine dimalate: inhibition of IL-7-dependent proliferation

Lymphopoiesis and myelopoiesis continuously generate mature cells from hematopoietic cell progenitors during the lifetime of the organism. The identification of new endogenous or exogenous substances that can act specifically on the differentiation of distinct cell lineages is of relevance and has potential therapeutical use. Kalanchoe brasiliensis (Kb) is a medicinal plant from the Crassulaceae family, used in folk medicine to treat inflammatory and infectious diseases. Here, we show that short-term treatment of naïve mice with Kb led to a strong and selective inhibition of lymphopoiesis, affecting B and T cell lineages without reduction of the myeloid lineage development. Similar effects were observed after treatment with the highly purified compound kalanchosine dimalate (KMC), obtained from Kb. Numbers of mature lymphocytes in secondary lymphoid organs were preserved in Kb(KMC)-treated mice. The effect of Kb(KMC) was not a result of secondary augmentation of plasma levels of endogenous corticoids; neither involves TNF-alpha, type-I IFN, or TLR2/TLR4 ligands, which have all been described as selective inhibitors of lymphopoiesis. Flow cytometry analysis of the phenotypes of T and B cell precursors indicate a blockade of maturation on IL-7-dependent, proliferative stages. In vitro, Kb(KMC) inhibited the IL-7-dependent proliferation of pre-B cells and does not induce massive apoptosis of B and T cell precursors. These results suggest that Kb(KMC) is selectively blocking lymphopoiesis through a mechanism that does not involve the previously characterized substances, possibly acting on the IL-7 signaling pathway, opening new perspectives for a potential therapeutic use of Kb-derived drugs.

Toll-like receptor 4 (TLR4)-dependent proinflammatory and immunomodulatory properties of the glycoinositolphospholipid (GIPL) from Trypanosoma cruzi

We have demonstrated recently that the glycoinositolphospholipid (GIPL) molecule from the protozoan Trypanosoma cruzi is a TLR4 agonist with proinflammatory effects. Here, we show that GIPL-induced neutrophil recruitment into the peritoneal cavity is mediated by at least two pathways: one, where IL-1beta acts downstream of TNF-alpha, and a second, which is IL-1beta- and TNFRI-independent. Moreover, NKT cells participate in this proinflammatory cascade, as in GIPL-treated CD1d(-/-) mice, TNF-alpha and MIP-2 levels are reduced significantly. As a consequence of this inflammatory response, spleen and lymph nodes of GIPL-treated mice have an increase in the percentage of T and B cells expressing the CD69 activation marker. Cell-transfer experiments demonstrate that T and B cell activation by GIPL is an indirect effect, which relies on the expression of TLR4 by other cell types. Moreover, although signaling through TNFRI contributes to the activation of B and gammadelta+ T cells, it is not required for increasing CD69 expression on alphabeta+ T lymphocytes. It is interesting that T cells are also functionally affected by GIPL treatment, as spleen cells from GIPL-injected mice show enhanced production of IL-4 following in vitro stimulation by anti-CD3. Together, these results contribute to the understanding of the inflammatory properties of the GIPL molecule, pointing to its potential role as a parasite-derived modulator of the immune response during T. cruzi infection.

Frequency of Natural Regulatory CD4+CD25+ T Lymphocytes Determines the Outcome of Tolerance across Fully Mismatched MHC Barrier through Linked Recognition of Self and Allogeneic Stimuli

We show in this study that long-term tolerance to allogeneic skin grafts can be established in the absence of immunosuppression by the combination of the following elements: 1) augmenting the frequency of regulatory CD4(+)CD25(+) T cells (Treg) and 2) presentation of the allogeneic stimuli through linked recognition of allo- and self-epitopes on semiallogeneic F(1) APCs. BALB/c spleen cells enriched for CD4(+)CD25(+) T lymphocytes were transferred either to BALB/c nu/nu mice or to BALB/c nu/nu previously injected with F(1)(BALB/c x B6.Ba) spleen cells, or else grafted with F(1)(BALB/c x B6.Ba) skin (chimeric BALB/c nu/nu-F(1)). Chimeric BALB/c nu/nu-F(1) reconstituted with syngeneic CD25(+)-enriched spleen cells were unable to reject the previously transferred F(1)(BALB/c x B6.Ba) spleen cells or F(1)(BALB/c x B6.Ba) skin grafts, and a specific tolerance to a secondary B6 graft was obtained, with rejection of third-party CBA grafts. BALB/c nu/nu mice reconstituted only with syngeneic CD25(+)-enriched spleen cells rejected both B6 and CBA skin grafts. In contrast, when chimeric BALB/c nu/nu-F(1) were reconstituted with spleen populations comprising normal frequencies of Treg cells, the linked recognition of allo and self resulted in breaking of self tolerance and rejection of syngeneic grafts, strongly suggesting that linked recognition works in both directions, either to establish tolerance to allo, or to break tolerance to self, the critical parameter being the relative number of Treg cells.

Role of TLR in B cell development: signaling through TLR4 promotes B cell maturation and is inhibited by TLR2

The role of TLR4 in mature B cell activation is well characterized. However, little is known about TLR4 role in B cell development. Here, we analyzed the effects of TLR4 and TLR2 agonists on B cell development using an in vitro model of B cell maturation. Highly purified B220(+)IgM(-) B cell precursors from normal C57BL/6 mouse were cultured for 72 h, and B cell maturation in the presence of the TLR agonists was evaluated by expression of IgM, IgD, CD23, and AA4. The addition of LPS or lipid A resulted in a marked increase in the percentage of CD23(+) B cells, while Pam3Cys had no effect alone, but inhibited the increase of CD23(+) B cell population induced by lipid A or LPS. The TLR4-induced expression of CD23 is not accompanied by full activation of the lymphocyte, as suggested by the absence of activation Ag CD69. Experiments with TLR2-knockout mice confirmed that the inhibitory effects of Pam3Cys depend on the expression of TLR2. We studied the effects of TLR-agonists on early steps of B cell differentiation by analyzing IL-7 responsiveness and phenotype of early B cell precursors: we found that both lipid A and Pam3Cys impaired IL-7-dependent proliferation; however, while lipid A up-regulates B220 surface marker, consistent with a more mature phenotype of the IgM(-) precursors, Pam3Cys keeps the precursors on a more immature stage. Taken together, our results suggest that TLR4 signaling favors B lymphocyte maturation, whereas TLR2 arrests/retards that process, ascribing new roles for TLRs in B cell physiology.

Expression of functional TLR4 confers proinflammatory responsiveness to Trypanosoma cruzi glycoinositolphospholipids and higher resistance to infection with T. cruzi

TLRs function as pattern recognition receptors in mammals and play an essential role in the recognition of microbial components. We found that the injection of glycoinositolphospholipids (GIPLs) from Trypanosoma cruzi into the peritoneal cavity of mice induced neutrophil recruitment in a TLR4-dependent manner: the injection of GIPL in the TLR4-deficient strain of mice (C57BL/10ScCr) caused no inflammatory response. In contrast, in TLR2 knockout mice, neutrophil chemoattraction did not differ significantly from that seen in wild-type controls. GIPL-induced neutrophil attraction and MIP-2 production were also severely affected in TLR4-mutant C3H/HeJ mice. The role of TLR4 was confirmed in vitro by testing genetically engineered mutants derived from TLR2-deficient Chinese hamster ovary (CHO)-K1 fibroblasts that were transfected with CD14 (CHO/CD14). Wild-type CHO/CD14 cells express the hamster TLR4 molecule and the mutant line, in addition, expresses a nonfunctional form of MD-2. In comparison to wild-type cells, mutant CHO/CD14 cells failed to respond to GIPLs, indicating a necessity for a functional TLR4/MD-2 complex in GIPL-induced NF-kappaB activation. Finally, we found that TLR4-mutant mice were hypersusceptible to T. cruzi infection, as evidenced by a higher parasitemia and earlier mortality. These results demonstrate that natural resistance to T. cruzi is TLR4 dependent, most likely due to TLR4 recognition of their GIPLs.

Regeneration of natural antibody repertoire after massive ablation of lymphoid system: robust selection mechanisms preserve antigen binding specificities

Natural Abs (NAbs) are Igs present in the serum and body fluids of healthy vertebrate animals, without any previous intentional immunization. NAbs often exhibit autoreactivity but also play an essential role in immunity, being a first line of defense against infectious microorganisms. We have previously analyzed the natural serum IgM Ab repertoire of normal mice, characterizing their reactivity with hundreds/thousands of self Ags; a significant similarity among different individuals was observed, and it was found that many reactivities of NAbs stably kept during adulthood were established early in life, implicating that period as a critical time window in the physiology of NAb repertoire selection. In the work reported here, experiments were conducted to address the role of normal lymphocyte ontogeny to the formation and stability of adult NAb repertoire. The massive destruction of the lymphoid system was promoted in adult mice with gamma-irradiation, and regeneration of hemopoietic tissues was granted by bone marrow or fetal liver inoculum. NAb repertoire regeneration was followed for 60 days after gamma-irradiation in bone marrow or fetal liver chimeric animals. The analysis of serum IgM reactivity with hundreds/thousands of self Ags showed that the NAb repertoire regenerated most of its original format after massive destruction of lymphoid compartments, characterizing autoreactive repertoire selection as a robust biological process. The data also show that regeneration of the NAb repertoire occurred similarly in fetal liver and bone marrow chimeras, although the latter animals poorly reconstituted their CD5(+) B1 cell compartment, suggesting that B1 cells are not essential for natural Ab regeneration.

Functional diversity of natural IgM

This paper proposes a method for the quantitative characterization of repertoire diversity of an unknown mixture of antibodies on the basis of its reactivity profile in the quantitative immunoblot (QIB). The QIB is calibrated by measuring the reactivity profiles of supernatants of known 'diversity' (i.e. known numbers of B cell clones). We define a quantitative 'index of variability' (IV) which decreases regularly as the diversity increases and the profiles tend towards a common 'convergence profile'. The calibration procedure is consolidated by a mathematical model based on the Poisson distribution; this theoretical model accounts correctly for the observed convergence behavior. On the basis of this calibration curve, it is possible to estimate the diversity of an unknown antibody mixture from a measure of its IV. We conclude that the functional diversity of natural serum IgM in mice can be estimated at approximately 16,000 clones.

Functional diversity and clonal frequencies of reactivity in the available antibody repertoire

The present experiments address functional antibody diversity and clonal distribution in murine available repertoires. IgM-containing supernatants were prepared by unbiased, polyclonal stimulation of resting splenic B cells from C57BL/6 mice, to ensure similar numbers of responding clones/culture and equivalent growth and maturation of all clones. The repertoires of clones and clonal mixtures were quantitatively assayed by limiting dilution analysis (LDA) on immunoblots of sodium dodecylsulfate polyacrylamide gel electrophoresis of homologous liver extracts, allowing to determine specific clonal frequencies towards the many hundred blotted antigens. The clonal frequency of reactivity of B cells with the extract was shown to be a bi-modal distribution of specific frequencies between 1/220 and 1/100,000. Cross-correlation analysis of reactivity to different bands in individual supernatants revealed low levels of cross-reactivity, suggesting that the blotted extract provides a very diverse set of antigens. Investigation of the affinity/concentration thresholds for detection of antigen-antibody interactions of our assay supports the notion that global repertoire analyses on immunoblots were highly discriminative and non-degenerate. Furthermore, reactivity patterns obtained with complex antibody mixtures correlated with the frequency of clonal reactivities as determined by LDA. The results demonstrate a large functional diversity of resting B lymphocytes, indicating a minimal repertoire size that is orders of magnitude higher than previous theoretical proposals suggested, and extensively heterogeneous in the size of clonal specificities.

Genetic control of natural antibody repertoires: I. IgH, MHC and TCR beta loci

Global analysis of natural antibody repertoires has revealed a marked conservation of reactivity patterns within inbred mouse strains, and characteristic strain-specific differences. We have now analyzed the genetic control of reactivity repertoires, aiming at identifying the respective selection mechanisms. Multiparametric statistics of a large number of serum antibody reactivities scored by quantitative Western blot analyses using extracts from homologous tissues and bacteria readily distinguish the reactivity patterns of C57BL/6 and BALB/c, revealing homogeneity among genetically identical individuals. Antibody repertoires in the prototype strains can also be segregated from those expressed by the respective IgH congenics, BC.8 and CB.20, demonstrating that IgH-linked genes contribute to determining natural antibody repertoires. Conversely, strains sharing IgH haplotype also express distinct reactivity patterns, indicating that other genes participate in the selection of serum IgM repertoires. Two such non-IgH loci were now identified. Thus, analysis of four MHC-congenic strains demonstrated that MHC-linked control of natural antibody repertoires is likely to operate through differential selection of T cell repertoires, since (1) mice that are congenic at the TCR beta locus, and (2) BALB/c nude mice grafted at birth with pure thymic epithelium from either C57BL/6 or BALB/c also differ in their natural antibody repertoires.

The repertoire of serum IgM in normal mice is largely independent of external antigenic contact

Antigen-free (AGF) and germ-free (GF) mice, although essentially free of serum IgG, maintain normal levels of circulating IgM. Using a quantitative immunoblot assay, we have now analyzed the repertoire of serum IgM from AGF, GF, and specific pathogen-free (SPF) BALB/c mice, on large panels of natural antigens from homologous tissues and bacteria. The reactivity profiles were very similar in the three groups of mice. Multiparametric statistic evaluation of the data showed that BALB/c animals, SPF, GF, and AGF mice constitute an homogeneous group with similar immunoreactivity profiles when compared to C57BL/6. Differences between immunoreactivity profiles of GF and AGF mice were observed, but were not statistically significant. These results suggest that the serum IgM repertoire of normal mice is strictly regulated and selected by endogenous ligands.

Characteristic generated alterations of autoantibody patterns in idiopathic thrombocytopenic purpura

Using a Western blot technique that allows quantitative detection of antibody reactivities to a large number of antigens, serum IgG and IgM antibody repertoires were compared in a group of 19 patients with a diagnosis of idiopathic thrombocytopenic purpura (ITP) and respective healthy controls. The results show that, irrespective of the duration of thrombocytopenia, age of the patients, and type of therapy, all ITP donors share characteristic alterations of serum antibody reactivity patterns on homologous erythrocyte and liver antigens. Multiparametric analyses of the immunoreactivity data readily segregated the groups of ITP and healthy donors. Similar analyses also distinguished ITP sera from those of a group of patients with systemic lupus erythematosus (SLE). We conclude that ITP is an autoimmune disease associated with generalized alterations of antibody repertoires, that may be characteristic enough to allow for diagnosis.

Instability of natural antibody repertoires in systemic lupus erythematosus patients, revealed by multiparametric analysis of serum antibody reactivities

Recent views on autoimmune diseases invoke generalized but specific perturbations in antibody repertoires, rather than the clonally restricted or non-specific polyclonal alterations proposed thus far. The present experiments analyse serum antibody reactivities in 24 systemic lupus erythematosus (SLE) patients and 17 healthy controls, using a method that quantitatively scores a large number of antibody reactivities and allows for multiparametric statistical analyses. The results show global but relatively specific perturbations in SLE antibody repertoires, and identify novel disease-associated reactivity patterns. Furthermore, a time series analysis of serum antibodies over 3 months demonstrates instability of natural antibody repertoires in individual SLE patients, contrasting with their remarkable conservation in healthy donors. Moreover, the method used clusters controls and patients independently, and might prove of diagnostic value, once large data bases are established.

The age-associated increase in autoreactive immunoglobulins reflects a quantitative increase in specificities detectable at lower concentrations in young mice

Serum immunoglobulins reactive with several autoantigens have been reported to increase with age. The authors have studied the reactivity of serum immunoglobulins from mice between 2 and 24 months of age with antigens present in lysates of syngeneic tissue extracts from young mice. The profile of immunoglobulin binding with the immunoblots of spleen and brain tissue increased progressively with age, showing only minor differences from mouse to mouse and, with one exception, revealing that the age-associated increase in binding of immunoglobulins occurred with antigens with the same migratory position in the immunoblots detectable, at lower concentration, in sera from young mice. Not all sera from older mice had increased immunoglobulin binding when tested with extracts of skin, muscle and liver but those that did expressed increased binding with antigens in all three lysates and with the same profile shown by sera from young mice. These results are consistent with the hypothesis that the age-associated increase in autoreactive immunoglobulins represents a selective increase in autoreactive specificities expressed by serum immunoglobulins from young animals at lower levels.

The self-reactive antibody repertoire of normal human serum IgM is acquired in early childhood and remains conserved throughout life

The authors have used a quantitative immunoblotting technique to analyse the antibody repertoire of IgM in cord blood and in the serum of young children, young adult males and aged males directed towards antigens in homologous tissues utilized as sources of self antigens. The reactivities of IgM with self antigens exhibited striking homogeneity and invariance among newborns. Self-reactive IgM repertoires of children, young adults and aged males were markedly conserved among individuals and comprised most of the anti-self reactivities that prevailed in neonates. Reactivities of IgM with bacterial antigens showed a high degree of homogeneity among newborns but were more diverse in children, young adults and elderly individuals. Diversity of IgM reactivities with self and non-self antigens did not vary significantly with aging. Principal component analysis (PCA) and linear discriminant analysis (LDA) of the data discriminated between self-reactive IgM repertoires of newborns and children, but failed to discriminate between repertoires of children, young adults and aged males. The data indicate that the self-reactive antibody repertoire of IgM differentiates during the first years of life and remains relatively constant thereafter.

Murine acariasis. II. Immunological dysfunction and evidence for chronic activation of Th-2 lymphocytes

The authors describe the immunological profile of BALB/c mice with Mite-Associated Ulcerative Dermatitis (MAUD)-like disease, due to Myocoptes musculinus (Koch 1844) infestation. The disease probably involves allergic mechanisms and is characterized by erythematous and pruritic skin lesions, widespread hair loss, lymphadenopathy, lymphocytopenia, granulocytosis and wasting. Affected individuals had much reduced numbers of pre-B and B cells in bone marrow and B cells in blood; decreased T-cell numbers in peripheral lymphoid organs and blood; hypergammaglobulinaemia with selective increases of IgG1, IgE and IgA, and depletion on IgM and IgG3, the same isotype distribution being detected in splenic plasmocytes; qualitative modifications of the serum antibody reactivity pattern; and increased production of IL-4 with decreased IL-2 production after in vitro polyclonal stimulation of T cells. Taken together, these results suggest that infestation by M. musculinus in BALB/c mice leads to a significant immunological disorder resulting in a T-helper-2 (Th-2) type response, with marked systemic consequences. This pathological condition may thus provide a useful model system for the immunobiological perturbation associated with chronic allergic disease.

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.

Invariance and restriction toward a limited set of self-antigens characterize neonatal IgM antibody repertoires and prevail in autoreactive repertoires of healthy adults

Analysis of the reactivity of IgM with self-antigens in tissues by a quantitative immunoblotting technique showed striking invariance among newborns in the human and in the mouse. The self-reactive repertoire of IgM of adults was also markedly conserved; it comprised most anti-self reactivities that prevailed among neonates. Multivariate analysis confirmed the homogeneity of IgM repertoires of neonates toward self- and non-self-antigens. Multivariate analysis discriminated between newborn and adult repertoires for reactivity with two of five sources of self-proteins and with non-self-antigens. Our observations support the concept that naturally activated B lymphocytes are selected early in development and throughout life for reactivity with a restricted set of self-antigens.

Analysis of natural and disease-associated autoantibody repertoires: anti-endothelial cell IgG autoantibody activity in the serum of healthy individuals and patients with systemic lupus erythematosus

The present study demonstrates that natural IgG with anti-endothelial cell activity is present in the serum of healthy individuals and in pooled normal human Ig. By using a novel method that allows for the simultaneous and quantitative assessment of reactivities of antibodies with a large number of antigens in tissues, we observed that natural anti-endothelial cell antibody (AECA) recognizes a restricted set of self antigens in endothelial cells that is conserved among healthy individuals. The extent to which natural AECA activity is expressed in serum and the pattern of reactivity of AECA with endothelial cell antigens showed little variability between individuals. Analysis of AECA in the serum of patients with systemic lupus erythematosus (SLE) revealed a higher amount of activity and a wider spectrum of antigenic specificities than that recognized by natural antibodies in endothelial cell extracts. AECA activity of IgG in whole serum was lower than that of purified IgG in the case of healthy individuals and showed little variation among individuals. In contrast, no difference was found between AECA activity of purified IgG and that of IgG in patients' serum suggesting that SLE sera lack the factors that control expression of AECA activity in the serum of healthy individuals. Our results indicate that natural autoantibodies recognize a restricted and conserved set of self antigens. Our observations further suggest that defective regulation of the expressed autoreactive B cell repertoire is the basis for expansion of novel clonal specificities and enhanced autoantibody activity in serum of patients with autoimmune disease.

Negative selection of multireactive B cell clones in normal adult mice

In the absence of intentional immunizations, normal mice produce natural antibodies that react with a variety of self and foreign antigens. We have now addressed the putative physiological selection of such reactivities and some of their clonal characteristics, by analyzing antibodies produced by B cells at different stages of differentiation. Using an antigen-specific spot-enzyme-linked immunosorbent assay (ELISA) with a panel of self and foreign antigens, we found that newly formed B cells, either from adult bone marrow or from newborn spleen, contain the highest frequencies of IgM antibodies with reactivities towards the panel. Resting peripheral B cells show lower frequencies of such antibodies, that are lowest among naturally activated splenic plasma cells. Analyses of monoclonal IgM antibodies derived from lipopolysaccharide-stimulated bone marrow and spleen cell hybridomas in normal mice show that the majority of reactivities scored in spot-ELISA originate from multireactive IgM clones. In Western blots against a large number of self antigens, each multireactive IgM antibody studied shows a unique and specific pattern of reactivity. We conclude that multireactive B cell clones are very frequent in the emergent repertoires of newborns and adults, but are subsequently negatively selected from bone marrow to periphery, and from the available repertoire to that of natural plasma cells. It, thus, seems that multireactivity of natural antibodies is not a positively selected property, but represents the sum of unique multireactive clones that have escaped inactivation or deletion.

Selectivity of recognition of variable (V) regions of autoantibodies by intravenous immunoglobulin (IVIg)

In the present study, we demonstrate that intravenous immunoglobulin (IVIg) is capable of binding to variable (V) regions of anti-endothelial cell antibodies (AECA) of healthy donors and patients with systemic lupus erythematosus (SLE). Among V regions of AECAs, IVIg selectively recognized certain idiotypes expressed by the autoantibodies of a given individual, in the case of both natural and SLE-associated AECAs. These observations provide new and direct evidence that IVIg interacts idiotypically with V regions of autoantibodies and that the efficacy of such interaction depends on individual autoantibody specificity. Our findings may be relevant for the understanding of the mechanisms that control expression of natural autoantibody activity in serum and for that of the differences in response to IVIg therapy that are seen between patients with autoimmune disease.

Global analysis of antibody repertoires. 1. An immunoblot method for the quantitative screening of a large number of reactivities

This paper describes a procedure for analysing multiple antibody reactivities that explores a commercially available immunoblot system, and is based on a double staining of nitrocellulose membranes, revealing both antibody reactivities and the migration position of the blotted proteins in the membrane. Quantification of both stainings by densitometry allowed the accurate superposition of the immunoreactivity and total protein profiles of each lane. Moreover, the protein stainings of the different lanes could be adjusted with a simple-scale transformation algorithm, correcting for possible distortions during electrophoretic migration, and allowing for the precise comparison of the immunoreactivity profiles in different lanes. The procedure is discriminatory enough to identify unique reactivity patterns in random pools of 10(4) activated B cells, and to define strain-specific natural antibody repertoires. The utility of this immunoblot method as an assay for simultaneously scoring multiple reactivities to hundreds of antigens in complex mixtures of antibodies, and thus defining antibody repertoires in a global manner, is discussed.

Global analysis of antibody repertoires. II. Evidence for specificity, self-selection and the immunological "homunculus" of antibodies in normal serum

The serum IgM repertoires of C57BL/6, DBA/2 and BALB/c mouse strains were analyzed using a recently developed global and quantitative assay that measures antibody reactivities to a very large number of antigens. A characteristic repertoire could be assigned to each strain. The different repertoires could be successfully classified with multivariate statistics. Many common reactivities were also observed among the different strains, which allows the definition of a mouse-specific repertoire. Analysis of human sera support this notion. To investigate the impact of minor genetic differences on the serum IgM repertoire, the congenic strains B10.D2/oSn and B10.D2/nSn, which differ in the expression of the C5 component of complement, were analyzed. The two strains could be separated based on the reactivity profiles obtained. The analysis of the results reveals that many antigenic proteins are not recognized at all by natural antibodies, while others are disproportionately reactive, the resulting patterns giving rise to what could be the definition of an "immunological homunculus". The relevance of this type of analysis for clinical applications is discussed.