Lack of mature B cells in nude mice with X-linked immune deficiency

B-CD8+ T Cell Interactions in the Anti-Idiotypic Response against a Self-Antibody

P3 is a murine, germline, IgM mAb that recognizes N-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+ T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+ T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VH region was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens.

Mediation of transitional B cell maturation in the absence of functional Bruton's tyrosine kinase

X-linked immune-deficient (Xid) mice, carrying a mutation in Bruton’s tyrosine kinase (Btk), have multiple B cell lineage differentiation defects. We now show that, while Xid mice showed only mild reduction in the frequency of the late transitional (T2) stage of peripheral B cells, the defect became severe when the Xid genotype was combined with either a CD40-null, a TCRbeta-null or an MHC class II (MHCII)-null genotype. Purified Xid T1 and T2 B cells survived poorly in vitro compared to wild-type (WT) cells. BAFF rescued WT but not Xid T1 and T2 B cells from death in culture, while CD40 ligation equivalently rescued both. Xid transitional B cells ex vivo showed low levels of the p100 protein substrate for non-canonical NF-kappaB signalling. In vitro, CD40 ligation induced equivalent activation of the canonical but not of the non-canonical NF-kappaB pathway in Xid and WT T1 and T2 B cells. CD40 ligation efficiently rescued p100-null T1 B cells from neglect-induced death in vitro. These data indicate that CD40-mediated signals, likely from CD4 T cells, can mediate peripheral transitional B cell maturation independent of Btk and the non-canonical NF-kappaB pathway, and thus contribute to the understanding of the complexities of peripheral B cell maturation.

CD4+ T cells and CD40 participate in selection and homeostasis of peripheral B cells

Control of peripheral B cell development and homeostasis depends critically on coordinate signals received through the BAFFRs and BCRs. The extent to which other signals contribute to this process, however, remains undefined. We present data indicating that CD4(+) T cells directly influence naive B cell development via CD40 signaling. Loss of CD4(+) T cells or CD40-CD40L interaction leads to reduced B cell homeostatic proliferation and hindered B cell reconstitution posttransplantation. Furthermore, we demonstrate that in the absence of CD40 signals, these events are modulated by BCR self-reactivity. Strikingly, murine models lacking CD40 reveal a broadly altered BCR specificity and limited diversity by both single-cell cloning and high-throughput sequencing techniques. Collectively, our results imply that any setting of T cell lymphopenia or reduced CD40 function, including B cell recovery following transplantation, will impact the naive B cell repertoire.

Reconstitution of immunodeficient SCID/beige mice with human cells: applications in preclinical studies

Experimental studies of the in vivo behaviour of human cells and tissues have become possible with the development of immunodeficient mice strains. Such mice accept readily allogeneic or xenogeneic grafts, including grafts of human cells or tissues, without rejection. In this review we describe different immunodeficient mouse strains that have been used for reconstitution by human immune cells. We subsequently go through the experience that we and others have had with reconstitution, and mention the adverse effects, in particular xenogeneic graft versus host reactions. The use of haematopoietic stem cells avoids such reactions but the immunological reconstitution may take several months. We then report the use of immunodeficient mice for the study of chronic vascular rejection of human mesenteric arteries due to cellular or humoral alloreaction. We have shown that SCID/beige mice grafted with a human artery at the place of the aorta developed a thickening of the intima of the human artery after 5-6 weeks, when they were reconstituted with spleen cells from another human donor. The thickening is mainly due to a proliferation of smooth muscle cells. The same type of lesion developed if they received injection of antibodies towards HLA class I antigens. The arteries of the mouse did not develop any lesion. The arterial lesions closely resembled those seen after clinical organ transplantation. Mice that received spleen cells from the same human donor developed little or no lesions. An important aspect of this experimental transplantation model is the possibility to test drugs that may be used in clinical transplantation. In recent experiments we have shown that novel immunosuppressive drugs can inhibit the hyperproliferation of smooth muscle cells in vitro. Preclinical testing in reconstituted SCID/beige mice grafted with human arteries will permit the evaluation of the potential use of these drugs to prevent chronic vascular rejection. The model also allows pharmacodynamic studies that give information on the biological impact of different drugs that may be used in experimental or clinical transplantation.

A New Molecular Genetic Diagnosis of the Btkxid Mice

A new method of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was developed for genetic typing of a point mutation of the Bruton's tyrosine kinase (Btk) gene in CBA/N mice bearing an X-linked recessive immunodeficiency (xid). Since restriction site useful for RFLP analysis does not exist in the spontaneous mutant Btk(xid) locus, an artificial restriction site was introduced by PCR amplification with a modified primer. The five genotypes of the Btk locus (Btk(xid)/ Btk(xid), Btk(xid) /Btk+ and Btk+/Btk+ females and Btk(xid)/Btk(null) and Btk+/Btk(null) males) could be distinguished by three patterns clearly and easily. This PCR-RFLP analytic method will be useful as a tool in the production of congenic mice and mice with multiple immunodeficient genes.

Naive CD4 T cells constitutively express CD40L and augment autoreactive B cell survival

Chronic engagement of the B cell receptor by soluble autoantigen leads to reduced B cell survival. Using the Ig and hen egg lysozyme double transgenic mouse model, we demonstrate that the survival of soluble autoantigen-engaged B cells is further reduced in mice lacking CD4 T cells or deficient in CD40. Mixed bone marrow chimera experiments reveal that, under homeostatic conditions, the CD40L-CD40 pathway can augment autoreactive B cell survival in a non-cell-autonomous manner. Naive CD4 T cells are shown to constitutively express CD40L mRNA and protein, although cell surface CD40L abundance is low because of engagement with CD40 on other cells. These observations indicate that the CD40L-CD40 pathway can augment the survival of autoantigen-engaged B cells in the absence of T cell activation. We propose that constitutive CD40L expression by naive CD4 T cells influences the composition of the B cell repertoire and may also affect the homeostasis of other cell types such as regulatory T cells in lymphoid organs.

T cells are required for the peripheral phase of B-cell maturation

B-lymphocyte maturation is considered to be independent of the thymus. However, there is circumstantial evidence suggesting that it may be impaired in nude animals that lack the thymus. Our study shows that the proportion of immature B-lymphocyte subsets (CD90(high) IgM(high) and CD90(high) IgM(low)) was significantly increased, whereas that of mature B-lymphocyte subsets (CD90- IgM(low) and CD90- IgM(high)) was decreased in the blood and lymph nodes of nude rats. In addition, the expression of major histocompatibility complex class II, intercellular adhesion molecule-1, CD44 and l-selectin was significantly down-regulated both on immature and mature B-lymphocyte subsets. After implantation of thymic tissue under the kidney capsule of nude rats the block in B-lymphocyte maturation was alleviated and the expression of surface molecules was normalized. Comparable effects were seen after the adoptive transfer of T lymphocytes. Thus, we show that in nude rats B cells do not mature properly because of the lack of T-cell help and that T lymphocytes are required for the peripheral phase of B-lymphocyte maturation, as well as for the appropriate expression of surface molecules. This should be considered when treating patients with T-cell deficiencies.

Reconstitution of a human immune system in immunodeficient mice: models of human alloreaction in vivo

Rodents have been widely used for studies in transplantation immunology because of their short reproduction period and the relative ease of generating inbred mutant or transgenic strains. However, although many biological mechanisms are similar between rodents and humans, several features clearly distinguish the immune system in these species. Consequently, it is rarely possible to extrapolate observations from rodent models directly into clinical practice. In vitro studies with human cells are useful for elucidation of basic mechanisms, but in order to study complex biological phenomena, in vivo studies are indispensable. In later years, a number of interesting models have been described where immunodeficient mice have been reconstituted with human cells, so-called humanized mice, in order to study human immune responses in vivo. This has opened a new field of experimental immunology that has been applied to areas such as cancer, autoimmunity, allergy, infections, and transplantation biology. In this review, we shall concentrate on the use of severe combined immunodeficient mice reconstituted with human immune or stem cells for studies of human alloreaction in vivo.

B cell signaling and tumorigenesis

The proliferation and differentiation of lymphocytes are regulated by receptors localized on the cell surface. Engagement of these receptors induces the activation of intracellular signaling proteins that transmit the receptor signals to distinct targets and control the cellular responses. The first signaling proteins to be discovered in higher organisms were the products of oncogenes. For example, the kinases Src and Abelson (Abl) were originally identified as oncogenes and were later characterized as important proteins for signal transduction in various cell types, including lymphocytes. Now, as many cellular signaling molecules have been discovered and ordered into certain pathways, we can better understand why particular signaling proteins are associated with tumorigenesis. In this review, we discuss recent progress in unraveling the molecular mechanisms of signaling pathways that control the proliferation and differentiation of early B cells. We point out the concepts of auto-inhibition and subcellular localization as crucial aspects in the regulation of B cell signaling.

Correction of X-Linked Immunodeficient Mice by Competitive Reconstitution With Limiting Numbers of Normal Bone Marrow Cells

Gene therapy for inherited disorders is more likely to succeed if gene-corrected cells have a proliferative or survival advantage compared with mutant cells. We used a competitive reconstitution model to evaluate the strength of the selective advantage that Btk normal cells have in Btk-deficient xid mice. Whereas 2,500 normal bone marrow cells when mixed with 497,500 xid cells restored serum IgM and IgG3 levels to near normal concentrations in 3 of 5 lethally irradiated mice, 25,000 normal cells mixed with 475,000 xidcells reliably restored serum IgM and IgG3 concentrations and the thymus-independent antibody response in all transplanted mice. Reconstitution was not dependent on lethal irradiation, because sublethally irradiated mice all had elevated serum IgM and IgG3 by 30 weeks postreconstitution when receiving 25,000 normal cells. Furthermore, the xid defect was corrected with as few as 10% of the splenic B cells expressing a normal Btk. When normal donor cells were sorted into B220+/CD19+ committed B cells and B220−/CD19− cell populations, only the B220−/CD19− cells provided long-term B-cell reconstitution in sublethally irradiated mice. These findings suggest that even inefficient gene therapy may provide clinical benefit for patients with XLA.

Tec family of protein-tyrosine kinases: an overview of their structure and function

The Tec family is a recently emerging subfamily of non-receptor protein-tyrosine kinases (PTKs) represented by its first member, Tec. This family is composed of five members, namely Tec, Btk. Itk/Emt/Tsk, Bmx and Txk/Rlk. The most characteristic feature of this family is the presence of a pleckstrin homology (PH) domain in their protein structure. The PH domain is known to bind phosphoinositides; on this basis, Tec family PTKs may act as merge points of phosphotyrosine-mediated and phospholipid-mediated signaling systems. Many Tec family proteins are abundantly expressed in hematopoietic tissues, and are presumed to play important roles in the growth and differentiation processes of blood cells. Supporting this, mutations in the Btk gene cause X chromosome-linked agammaglobulinemia (XLA) in humans and X chromosome-linked immunodeficiency (Xid) in mice, indicating that Btk activity is indispensable for B-cell ontogeny. In addition, Tec family kinases have been shown to be involved in the intracellular signaling mechanisms of cytokine receptors, lymphocyte surface antigens, heterotrimeric G-protein-coupled receptors and integrin molecules. Efforts are being made to identify molecules which interact with Tec kinases to transfer Tec-mediated signals in vivo. Candidates for such second messengers include PLC-gamma2, guanine nucleotide exchange factors for RhoA and TFII-I/BAP-135. This review summarizes current knowledge concerning the input and output factors affecting the Tec kinases.

Regulation of nuclear localization and transcriptional activity of TFII-I by Bruton's tyrosine kinase

Bruton's tyrosine kinase (Btk) is required for normal B-cell development, as defects in Btk lead to X-linked immunodeficiency (xid) in mice and X-linked agammaglobulinemia (XLA) in humans. Here we demonstrate a functional interaction between the multifunctional transcription factor TFII-I and Btk. Ectopic expression of wild-type Btk enhances TFII-I-mediated transcriptional activation and its tyrosine phosphorylation in transient-transfection assays. Mutation of Btk in either the PH domain (R28C, as in the murine xid mutation) or the kinase domain (K430E) compromises its ability to enhance both the tyrosine phosphorylation and the transcriptional activity of TFII-I. TFII-I associates constitutively in vivo with wild-type Btk and kinase-inactive Btk but not xid Btk. However, membrane immunoglobulin M cross-linking in B cells leads to dissociation of TFII-I from Btk. We further show that while TFII-I is found in both the nucleus and cytoplasm of wild-type and xid primary resting B cells, nuclear TFII-I is greater in xid B cells. Most strikingly, receptor cross-linking of wild-type (but not xid) B cells results in increased nuclear import of TFII-I. Taken together, these data suggest that although the PH domain of Btk is primarily responsible for its physical interaction with TFII-I, an intact kinase domain of Btk is required to enhance transcriptional activity of TFII-I in the nucleus. Thus, mutations impairing the physical and/or functional association between TFII-I and Btk may result in diminished TFII-I-dependent transcription and contribute to defective B-cell development and/or function.

Bruton's tyrosine kinase controls a sustained calcium signal essential for B lineage development and function

Genetic data support a role for Btk during the B lineage development transitions regulated by signaling through both the pre-B and the B cell antigen receptors. Dysregulated signaling at each of these transitions can result in failure of these cell populations to proliferate and subsequent cell death. Btk-dependent IP3 production is crucial for maintaining the sustained calcium signal in response to BCR engagement and is likely to regulate a subset of transcriptional events essential for B lineage growth or survival. Identification of these Btk-dependent signals will be important in understanding B cell activation, differentiation, and cell death. This information may lead to therapies specifically targeting these events in B cell autoimmunity or malignancy and provide a fuller understanding of the appropriate target populations and potential negative consequences of Btk gene therapy in XLA. Identification of Btk/Tec family kinases in an increasing number of vertebrate and invertebrate cell lineages suggests that the link between Btk and the PLC gamma/IP3/calcium signaling pathways may be broadly conserved.

B-1 cell development: evidence for an uncommitted immunoglobulin (Ig)M+ B cell precursor in B-1 cell differentiation

Murine phosphatidyl choline (PtC)-specific B cells in normal mice belong exclusively to the B-1 subset. Analysis of anti-PtC (VH12 and VH12/Vkappa4) transgenic (Tg) mice indicates that exclusion from B-0 (also known as B-2) occurs after immunoglobulin gene rearrangement. This predicts that PtC-specific B-0 cells are generated, but subsequently eliminated by either apoptosis or differentiation to B-1. To investigate the mechanism of exclusion, PtC-specific B cell differentiation was examined in mice expressing the X-linked immunodeficiency (xid) mutation. xid mice lack functional Bruton's tyrosine kinase (Btk), a component of the B cell receptor signal transduction pathway, and are deficient in B-1 cell development. We find in C57BL/ 6.xid mice that VH12 pre-BII cell selection is normal and that PtC-specific B cells undergo modest clonal expansion. However, the majority of splenic PtC-specific B cells in anti-PtC Tg/xid mice are B-0, rather than B-1 as in their non-xid counterparts. These data indicate that PtC-specific B-0 cell generation precedes segregation as predicted, and that Btk function is required for efficient segregation to B-1. Since xid mice exhibit defective B cell differentiation, not programmed cell death, these data are most consistent with an inability of PtC-specific B-0 cells to convert to B-1 and a single B cell lineage.

B-cell receptor regulation of peripheral B cells

Recent studies indicate that immature B cells compete with recirculating B cells for survival signals. The signals, delivered through the B-cell receptor for antigen, induce immature cells to differentiate into recirculating cells and maintain the survival of recirculating cells. They do not induce proliferation or differentiation to antibody-producing cells.

An essential role for Bruton's [corrected] tyrosine kinase in the regulation of B-cell apoptosis

Mutations of the Bruton's tyrosine kinase (btk) gene cause X-linked agammaglobulinemia (XLA) in humans and X-linked immune deficiency (Xid) in mice. To establish the BTK role in B-cell activation we examined the responses of wild-type and Xid B cells to stimulation through surface IgM and CD40, the transducers of thymus independent-type 2 and thymus-dependent activation, respectively. Wild-type BTK was necessary for proliferation induced by soluble anti-IgM (a prototype for thymus independent-type 2 antigen), but not for responses to soluble CD40 ligand (CD40L, the B-cell activating ligand expressed on T-helper cells). In the absence of wild-type BTK, B cells underwent apoptotic death after stimulation with anti-IgM. In the presence of wild-type but not mutated BTK, anti-IgM stimulation reduced apoptotic cell death. In contrast, CD40L increased viability of both wild-type and Xid B cells. Importantly, viability after stimulation correlated with the induced expression of bcl-XL. In fresh ex vivo small resting B cells from wild-type mice there was only barely detectable bcl-XL protein, but there was more in the larger, low-density ("activated") splenic B cells and peritoneal B cells. In vitro Bcl-XL induction following ligation of sIgM-required BTK, was cyclosporin A (CsA)-sensitive and dependent on extracellular Ca2+. CD40-mediated induction of bcl-x required neither wild-type BTK nor extracellular Ca2+ and was insensitive to CsA. These results indicate that BTK lies upstream of bcl-XL in the sIgM but not the CD40 activation pathway. bcl-XL is the first induced protein to be placed downstream of BTK.

Defective B cell development and function in Btk-deficient mice

Mutations in the Bruton's tyrosine kinase (Btk) gene have been linked to severe early B cell developmental blocks in human X-linked agammaglobulinemia (XLA), and to milder B cell activation deficiencies in murine X-linked immune deficiency (Xid). To elucidate unequivocally potential Btk functions in mice, we generated mutations in embryonic stem cells, which eliminated the ability to encode Btk pleckstrin homology or kinase domains, and assayed their effects by RAG2-deficient blastocyst complementation or introduction into the germline. Both mutations block expression of Btk protein and lead to reduced numbers of mature conventional B cells, severe B1 cell deficiency, serum IgM and IgG3 deficiency, and defective responses in vitro to various B cell activators and in vivo to immunization with thymus-independent type II antigens. These results prove that lack of Btk function results in an Xid phenotype and further suggest a differential requirement for Btk during the early stages of murine versus human B lymphocyte development.

Impaired expansion of mouse B cell progenitors lacking Btk

Mutations in the gene encoding the protein tyrosine kinase Btk are associated with the human B cell immunodeficiency X-linked agammaglobulinemia (XLA). In the mouse, a point mutation in the Btk pleckstrin homology domain segregates with a milder X-linked immunodeficiency (xid). To assess the importance of Btk function in murine lymphopoiesis, we generated multiple embryonic stem cell clones bearing a targeted disruption of the btk gene and examined their potential to produce lymphocytes in both C57BL/6 and RAG2-/- host chimeric animals. These mice provide a complementary set of in vivo competition assays that formally establish the genetic basis for the xid phenotype. Although the null mutation yields a phenotype quite similar to that of xid, it also compromises expansion of B cell precursors. Our results suggest that the murine and human consequences of Btk deficiency differ only quantitatively, and represent the same disease process.

CD4+ T cells determine the ability of spleen cells from F1 hybrid mice to induce neonatal tolerance to alloantigens and autoimmunity in parental mice

Spleen cells from F1 hybrid mice injected into newborn parental mice induce a state of cytolytic unresponsiveness to the corresponding alloantigens. However, these mice develop a transient autoimmune syndrome characterized by the production of multiple autoantibodies and glomerulonephritis. Previous reports indicated that the depletion of F1 donor T cells, shortly prior the injection into parental mice, does not interfere with any of these events. Here, we have explored whether the continuous absence of T cells in F1 mice influences the ability of their spleen cells to induce neonatal tolerance to alloantigens and the associated autoimmune manifestations. Our results revealed that spleen cells from athymic (BALB/c x C57BL/6) F1 hybrid (CB6F1) nu/nu mice or from euthymic CB6F1 mice depleted from birth of CD4+ T cells, but not of CD8+ T cells, are unable to induce neonatal tolerance to alloantigens and autoimmune manifestations. By contrast, the partial reconstitution of T cells in CB6F1 nu/nu mice, after the neonatal graft of a syngeneic thymus, restored the capacity of spleen cells from these mice to induce tolerance and autoimmunity when injected into newborn BALB/c mice. These results demonstrate that the functional defect of spleen cells from athymic CB6F1 nu/nu mice to induce neonatal tolerance to alloantigens is directly related to the long-term absence of mature CD4+ T cells. Interestingly, a new increase in the titers of anti-DNA Ab was observed when spleen cells from athymic CB6F1 nu/nu mice were injected into adult BALB/c mice that had been tolerized at birth with normal CB6F1 spleen cells. This finding indicates that B cells from CB6F1 nu/nu mice recover their capacity to interact with alloreactive Th2 cells when they are placed into mice having functional CD4+ T cells. These data indicate that the continuous absence of CD4+ T cells causes a reversible functional defect in F1 spleen cells that determines their inability to induce neonatal tolerance and autoimmunity.

The nude mutation results in impaired primary antibody repertoire

We have studied the effect of the nude mutation and/or T lymphocytes on the development of V gene germ-line repertoire in neonatal athymic (nu/nu) and euthymic (+/nu) littermates. A total of 2.35 x 10(6) and 1.47 x 10(6) B lymphocyte clones from nu/nu and +/nu neonates, respectively, were examined for the expression of select VH (J558, J606, S107, 36-60, 7183 and Q52) and Vx (1, 2, 8 and 9) gene families as well as VH (J558, S107) + Vx (1, 9) associations. Data showed that the nude mutation, whether homozygous or heterozygous, significantly affects VH and Vx gene expression as well as VH and Vx pairings and, thus, provide evidence for a defective development of B cell repertoire in both athymic nude (nu/nu) and euthymic (+/nu) mice. In addition, an analysis of 3.34 x 10(6) B lymphocyte clones from adult C57BL/6 mice showed non-stochastic association between VHJ558 + Vx1 gene families that suggests restrictions on clonal population in order to maintain homeostasis in the immune system. Studies outlined here, therefore, describe an hitherto unknown defect in the development of B lymphocyte repertoire as a result of the nude mutation which is independent of thymic dysgenesis.

X-linked agammaglobulinemia: new approaches to old questions based on the identification of the defective gene

The identification of a cytoplasmic tyrosine kinase, Btk, as the defective protein in human XLA and xid in the mouse, supports the hypothesis that both disorders are due to defects in B-cell activation or differentiation. Phenotypic analysis of B-lineage cells and studies on X-chromosome inactivation patterns in both mice and human patients suggest that mutations in Bth do not affect entry of stem cells into the B-lineage pathway but they do inhibit progression at multiple steps along that pathway. Although the exact function of Btk in signal transduction is not yet known, it is probable that studies which correlate specific mutations in different patients with alterations in Btk function will provide clues about critical sites in the molecule. Diagnosis and genetic counseling for families at risk of carrying the gene for XLA will be improved almost immediately by the identification of the responsible gene. Improvements in therapy may come more slowly. The possibility of curative gene therapy is attractive; however, there are several features of Btk that suggest that this will be a challenging undertaking. Overexpression or expression in inappropriate cell lineages may carry unacceptable risks. Mutant proteins may interfere with the function of wild-type proteins provided by gene therapy. However, it is likely that a better understanding of Btk function and regulation will benefit not only patients with XLA but also other patients with defects in B-cell function.

Organ-specific metastases in melanoma: experimental animal models

Metastases from certain primary tumors frequently exhibit specific organ preference. Animal models have been developed to induce in a reproducible fashion the formation of organ-specific metastases by malignant melanoma cells. Some of these models rely on the use of immunodeficient mice, which can support the growth of murine as well as human malignant melanomas. Moreover, immunodeficient mice, because of their diminished ability to mount an effective immune response, allow the expression of malignant properties (e.g., preferential colonization of certain organs), which are intrinsic to transplanted melanoma cells. This review discusses the relevant factors (and limitations) of some of the animal models used to study the in vivo properties of melanoma cells.

Colocalization of X-linked agammaglobulinemia and X-linked immunodeficiency genes

Mice that bear the X-linked immunodeficiency (xid) mutation have a B lymphocyte-specific defect resulting in an inability to make antibody responses to polysaccharide antigens. A backcross of 1114 progeny revealed the colocalization of xid with Bruton's agammaglobulinemia tyrosine kinase (btk) gene, which is implicated in the human immune deficiency, X-linked agammaglobulinemia. Mice that carry xid have a missense mutation that alters a highly conserved arginine near the amino-terminus of the btk protein, Btk. Because this region of Btk lies outside any obvious kinase domain, the xid mutation may define another aspect of tyrosine kinase function.

Role of x-linked immunodeficiency (xid) and NK activity in rejection of human tumor xenotransplants in nude mice

In order to elucidate the factors influencing the takes of human tumor xenografts in nude mice, we compared the transplantability of human tumors in nude mice with additional genetic defects in the immune system. The nude mice strains tested were classified as follows by expression of the beige gene and the x-linked immunodeficiency (xid) gene: 1) high NK nude (C57BL/6N, nu/nu), 2) low NK nude (C57BL/6 bg/bg nu/nu), 3) high NK nude with B-cell defect (CBA/N nu/nu), and 4) low NK nude with B-cell defect (NIH(S)III). Takes of human tumor xenografts including gastric carcinoma, T-cell lymphoma and B-cell lymphoma were better in nude mice with xid (CBA/N and NIH(S) III nude mice) than in nude mice without xid (B6 and beige nude mice). In addition, among the nude mice with xid expression, the takes were slightly better in nude mice with a CBA/N background than in those with a NIH(S) background. Moreover, the xenotransplantation rate in (CBA/N x C57BL/6N)F1 male nude mice with xid expression was higher than in (C57BL/6N x CBA/N)F1 males without xid expression, but did not react the same level as that in CBA/N nude. On the other hand, introduction of the beige gene into nude mice minimally improved the takes of human tumor xenografts under limited experimental conditions (inoculation of 100 x 10(5) T-cell lymphoma and 1 x 10(5) gastric carcinoma cells) despite the reduction of NK activity. In xenotransplantation of human tumors directly from patients, the take rates of the tumors were also better in CBA/N nude mice than in BALB/cA nude mice. The results in the present report confirmed the effect of xid and CBA/N genetic background on human tumor xenografts in nude mice, suggesting the existence of serum factors, possibly present in serum IgM, mediating rejection of the xenografts.

Production of 17.2.25 mu transgenic and endogenous immunoglobulin in X-linked immune deficient mice

In M54 mice transgenic for a completely rearranged mu(a) heavy chain there is a decrease in total B cells and the rearrangement of endogenous immunoglobulin genes is partially inhibited. Surprisingly, however, endogenous immunoglobulin gene rearrangement and significant heavy chain polypeptide production does occur. We tested the hypothesis that only CD5+ B cells produce endogenous immunoglobulin by taking advantage of the fact that X-linked immune deficient (xid) mice normally are deficient in CD5+ B cells. We found that the frequency of CD5+ splenic B cells was similar in XxidY transgenic and non-transgenic F1 males, and in XxidX transgenic and non-transgenic F1 females. In both XxidX and XxidY transgenic F1 mice some, but not all, splenic B cells are CD11b+. There was a striking deficit of splenic B cells expressing endogenous immunoglobulin in XxidY transgenic mice, although this was not true for peritoneal cells. Thus, the introduction of the 17.2.25 mu transgene does not prevent the development of CD5- B cells nor does it limit endogenous immunoglobulin gene arrangement and expression solely to CD5+ B cells. However, in mice capable of expressing B cell surface CD5 or CD11 this transgene can lead to expansion of the fraction of B cells positive for these molecules. We conclude that while the introduction of the 17.2.25 mu transgene alters the frequencies of B cell populations, maturation is not limited to one subpopulation.

Surface markers, heavy chain sequences and B cell lineages

A unifying theory of B cell development and lineage commitment is presented. There are two firmly established B lineages: cells which normally arise only from fetal sources and lack N insertions in their rearranged heavy chains; and N-containing cells which arise from adult bone marrow precursors (and perhaps from late fetal sources). Commitment to the expression of CD5 and the capacity for long-life (or self-renewal) are induced as a consequence of sIg cross-linking, typically by a repeating epitope, thymus independent type two antigen. Alternatively, activation resulting from cognate interaction with a helper T cell does not induce CD5 but results in lower expression of J11d. In this case activation occurs in the absence of sIg cross-linking. It is further proposed that differences in the Ig repertoire make it highly likely that fetal/neonatal, but not adult derived B cells will be induced to express CD5. The model offers a plausible explanation for the correlation of CD5 expression and natural autoantibody production by neonatal B cells. Possible sources of pathogenic autoantibody are discussed in the context of this model.

Immunological mutants of the mouse

Mutations at more than 30 loci in mice have been shown to cause deleterious effects on the immune system. Immunologic defects caused by certain of these mutations are determined at the level of hematopoietic progenitor cells or at the level of hematopoietic cell-stromal cell interactions. The immunological mutants described in this paper serve as experimental tools with which to increase our understanding of the development and regulation of the mammalian immune system.

Heterogeneity of thymic epithelial cells in promoting T-lymphocyte differentiation in vivo

To study in vivo the contribution of different thymic epithelial cells to T-lymphocyte differentiation, we have established several nontransformed thymic epithelial cell lines and developed an in vivo assay, not involving exposure to drugs or radiation, that permitted us to study the capacity of these epithelial lines to support T-cell differentiation. We found that cell lines EA2 and ET, which express markers of cortical epithelial cells, produce interleukin 7 mRNA and after being injected into the spleens of young athymic nude mice support in vivo generation of CD4+CD8- T-cell receptor alpha beta+ T lymphocytes (ET line) or both CD4+CD8- and CD4-CD8+ T-cell receptor alpha beta+ T cells (EA2 line). Both cell lines also supported generation of T-cell receptor gamma delta+ T cells but appear not to support development of double-positive (CD4+CD8+) cells. One cell line, EB3, which expresses markers of medullary epithelial cells, produces interleukin 1 alpha RNA transcripts but does not support T-lymphocyte differentiation. The results provide direct evidence for functional heterogeneity of thymic epithelial cells in vivo and show the involvement of different cortical epithelial cells in the differentiation of T-cell progenitors into distinct thymocyte subsets.

Immunoglobulin isotypes of C57BL/6 nu/nu, lpr/lpr mice. Lack of direct intrinsic effect of the lpr gene on B cell hyperactivity

The absolute concentrations of mouse immunoglobulin (Ig) heavy chain isotypes were determined by specific ELISAs in the serum of C57BL/6 (B6) mice doubly homozygous at the nude (nu) and the lymphoproliferation (lpr) locus (B6 nu, lpr mice), and compared with normal B6 nu mice. The distribution and the absolute concentrations of all Ig isotypes were found to be very similar in B6 nu, lpr and B6 nu mice, for both sexes and with similar increases in titers with ageing. Thus, the major part of the severe autoimmunity and hyperglobulinemia characteristic of the lpr syndrome of euthymic B6 lpr mice, including their elevated titers of thymus-independent IgM and IgG3 isotypes, is abrogated by the nude mutation, an effect of which is the lack of thymus differentiation. Though a postulated intrinsic activity of the lpr gene directly on B cell hyperactivity cannot be discarded, its expression would then require the presence of either the thymus or of T cells or of other cells or factors whose expression is also abrogated by the homozygosity at the nude locus.

Lymphoid cell transfers between adult C57BL/6 mice differing at the lpr and/or nu locus. Humoral immunity phenotype of the chimeras

Congenic C57BL/6 mice (B6) homozygous only at the nu (nude, athymic) locus (B6 nu) or also at the lpr (lympho-proliferation) locus (B6 nu, lpr) were used as recipients for the transfer of spleen and/or lymph node cells from either normal B6 mice (B6+) or lpr-homozygous B6 mice (B6 lpr). Highly increased survival was obtained for [B6 lpr----B6 nu, lpr] chimeras, but not for [B6+----B6 nu, lpr] and [B6 nu----B6 nu, lpr] chimeras. All long-term survivors that were killed showed an increased responsiveness to the T-cell mitogen concanavalin A (Con A) but no change of responsiveness to the B-cell mitogen lipopolysaccharide (LPS). Some enlargement of spleen and lymph nodes was observed only in some specific [B6----B6 nu, lpr] chimeras (female recipients of spleen cells). Within a few weeks after cell grafting, all but [B6 nu----B6 nu, lpr] chimeras developed highly increased levels of serum immunoglobulins, as well as a higher occurrence of anti-single-stranded (ss) DNA containing sera. These chimeras had been constructed in order to dissect the components of the lpr phenotype etiopathology (primordial involvement of B and/or T lineage cells, lymphoid and/or environmental influences). Though the evolution of serological parameters showed some chimera type-specific features, it seems difficult to reconstitute the entire expression of the lpr phenotype.

B cell precursors are present in the thymus during early development

An in vitro system for transforming immature lymphoid cells present in the thymus at early development has been established. By phenotype analysis of the transformants obtained, we observed that B cell precursors, susceptible to Abelson murine leukemia virus (A-MuLV)- or Harvey murine sarcoma virus (H-MuSV)-induced lymphogenesis, were present at high frequency in the fetal thymus of BALB/c mice. These precursors recolonized alymphoid thymus lobes in vitro, as do T cell precursors. It was further observed that B precursors in the fetal liver were also capable of recolonizing alymphoid thymus lobes and were stored in a thymic environment. These results suggest that stroma cells of the fetal thymus may possess the capacity to support the growth of B precursors. On the other hand, B cell precursors sensitive to the viral transformation were undetectable in the fetal thymus of C57BL/6, although immunohistochemical analysis suggested their presence. However, in the fetal liver of the same strain, B precursors recolonizing alymphoid thymus in vitro were sensitive to the viral transformation. Based on these results, we will discuss both the role and fate of thymic B precursors. In addition, we also obtained T cell lymphomas at different stages of differentiation from the fetal thymus of C57BL/6 infected with A-MuLV or H-MuSV. These data indicate the usefulness of our system in establishing cell lines derived from intrathymic lymphogenesis at early development.

Strain variation in the frequency of Abelson murine leukemia virus-transformed fetal liver pre-B cells bearing complete immunoglobulin heavy chain rearrangements

Fetal liver Abelson pre-B cell lines obtained from CBA/Tufts.xid and (CBA/Tufts.xid x CBA/Tufts)F1 mice have complete VDJH rearrangements on at least one allele. Such high frequencies of VDJH rearrangements have previously been observed in adult derived but not fetal liver derived Abelson pre-B cell lines. Genetic analyses suggest that CBA/Tufts.xid carries an autosomal dominant gene(s) that determines the predominance of VDJH rearrangements among transformants. This autosomal gene(s) might affect the intrinsic development of the early B cell lineage in the fetus or the fetal microenvironment, expanding pre-B cells of the "more mature" VDJH phenotype.

Nonrandom X chromosome inactivation in B cells from carriers of X chromosome-linked severe combined immunodeficiency

X chromosome-linked severe combined immunodeficiency (XSCID) is characterized by markedly reduced numbers of T cells, the absence of proliferative responses to mitogens, and hypogammaglobulinemia but normal or elevated numbers of B cells. To determine if the failure of the B cells to produce immunoglobulin might be due to expression of the XSCID gene defect in B-lineage cells as well as T cells, we analyzed patterns of X chromosome inactivation in B cells from nine obligate carriers of this disorder. A series of somatic cell hybrids that selectively retained the active X chromosome was produced from Epstein-Barr virus-stimulated B cells from each woman. To distinguish between the two X chromosomes, the hybrids from each woman were analyzed using an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. In all obligate carriers of XSCID, the B-cell hybrids demonstrated preferential use of a single X chromosome, the nonmutant X, as the active X. To determine if the small number of B-cell hybrids that contained the mutant X were derived from an immature subset of B cells, lymphocytes from three carriers were separated into surface IgM positive and surface IgM negative B cells prior to exposure to Epstein-Barr virus and production of B-cell hybrids. The results demonstrated normal random X chromosome inactivation in B-cell hybrids derived from the less mature surface IgM positive B cells. In contrast, the pattern of X chromosome inactivation in the surface IgM negative B cells, which had undergone further replication and differentiation, was significantly nonrandom in all three experiments [logarithm of odds (lod) score greater than 3.0]. These results suggest that the XSCID gene product has a direct effect on B cells as well as T cells and is required during B-cell maturation.

Development of Ly-1+ B cells in immunodeficient CBA/N mice

Spleen cells from CBA/N mice developing a systemic autoimmune disease after daily injection of CsA during an autologous bone marrow reconstitution were transferred into unmanipulated syngeneic recipients. Adoptive transfer allowed the development of Ly-1+ B cells, which shared Mac-1 differentiation antigen expression with the myelomonocytic lineage. Interestingly, expansion of formerly absent Ly-1+ B cells was paralleled by a severe reduction in common, Ly-1-, B cell development in the recipient. We conclude that precursors for Ly-1+ B lineage do exist in CBA/N mice.

Basal and lipopolysaccharide-inducible membrane alkaline phosphatase of lymphoid cells from mice with immune system dysfunctions

The expression of membrane alkaline phosphatase (mAlPase) activity is an enzymatic marker of activated but not resting B cells which can be used on unseparated lymphoid cell suspensions. It is higher in lymphoid cell suspensions from mice with higher proportions of B cells (athymic mice) or with more activated B cells (autoimmune mice) than in those of control mice.

Development of plasmacytoid cells with Russell bodies in autoimmune "viable motheaten" mice

Mice homozygous for the autosomal recessive mutation "viable motheaten" (mev) are severely immunodeficient, show polyclonal B-cell activation, and express multiple autoantibodies over a maximum life span of 25 weeks. Lymphoid tissues from these mice contain large numbers of atypical plasma cells in which discrete glycoprotein inclusions are found within the endoplasmic reticulum. Such plasma cells are termed "Mott cells," and the inclusions are called "Russell bodies." Dense accumulations of Mott cells are present in the marginal zones of the spleen and in the lymph nodes of mev/mev mice. Russell bodies in Mott cells from mev/mev mice contain immunoglobulin (Ig) as shown by immunofluorescence microscopy at the light-microscopic level and by indirect protein A-immunogold localization at the electron-microscopic level. Ultrastructural analyses reveal the presence of amorphous, lamellar, and crystalline Russell bodies. These Ig crystals have a periodicity of 150-190 A. Lymph node cell preparations which were enriched in Mott cells by velocity sedimentation failed to secrete Ig in a polyclonal reverse plaque assay. An obligate role of the thymus in Mott cell development is evidenced by the absence of Mott cells in neonatally thymectomized mev/mev mice and in mice doubly homozygous for the nude (nu) and mev mutations. These data suggest that Mott cells in mev/mev mice are thymic-dependent plasmacytoid cells resulting from chronic B-cell activation accompanied by impaired Ig secretion.

Thymus grafts induce B cell development in nude, X-linked immune deficient mice

Mice simultaneously expressing the mutations nude and X-linked immune deficiency (xid) were previously shown to have pro-B cells and/or early pre-B cells while lacking C mu+ and surface Ig+ cells. We now report that thymus grafts restore both T cells and B cells in nude-xid mice. By the use of Thy-1 and Igh allogeneic donors it was shown that both the T and B cells were host derived. The B cells had a functional phenotype typical of xid mice. It is concluded that the maturation of xid B cells past the pro-B or early pre-B stage is T cell dependent.

Functional analysis of influenza-specific helper T cell clones in vivo. T cells specific for internal viral proteins provide cognate help for B cell responses to hemagglutinin

We compared the effects of adoptively transferred Th cell clones specific for the influenza hemagglutinin (HA), matrix (M), or nucleoprotein (NP) on the antibody response of nude mice infected with A/PR/8/34 influenza virus. We show that the production of antibodies to the HA absolutely requires the presence of virus-specific Th cells. Further, transfer of a Th clone specific for the internal proteins, M or NP, was as effective as was transfer of an HA-specific clone in supporting an antibody response to the HA. With each of the clones, the kinetics of the response were accelerated by approximately 3 d compared with the antibody response of normal BALB/c mice. The HA- and M-specific clones supported an isotype switch from IgM to IgG and IgA similar to that which occurs during a normal antibody response. Finally, as shown by coinfection experiments, the response required a cognate T-B interaction whether the determinants recognized by the Th and B cell are located on the same viral protein or on different viral proteins within the same virus particle. The implications of these findings for understanding the T-B interactions that occur during an effective antiviral antibody response are discussed.