B-cell differentiation in the bone marrow and the periphery

Chronic Lymphocytic Leukemia B-Cell Normal Cellular Counterpart: Clues From a Functional Perspective

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of small mature-looking CD19+ CD23+ CD5+ B-cells that accumulate in the blood, bone marrow, and lymphoid organs. To date, no consensus has been reached concerning the normal cellular counterpart of CLL B-cells and several B-cell types have been proposed. CLL B-cells have remarkable phenotypic and gene expression profile homogeneity. In recent years, the molecular and cellular biology of CLL has been enriched by seminal insights that are leading to a better understanding of the natural history of the disease. Immunophenotypic and molecular approaches (including immunoglobulin heavy-chain variable gene mutational status, transcriptional and epigenetic profiling) comparing the normal B-cell subset and CLL B-cells provide some new insights into the normal cellular counterpart. Functional characteristics (including activation requirements and propensity for plasma cell differentiation) of CLL B-cells have now been investigated for 50 years. B-cell subsets differ substantially in terms of their functional features. Analysis of shared functional characteristics may reveal similarities between normal B-cell subsets and CLL B-cells, allowing speculative assignment of a normal cellular counterpart for CLL B-cells. In this review, we summarize current data regarding peripheral B-cell differentiation and human B-cell subsets and suggest possibilities for a normal cellular counterpart based on the functional characteristics of CLL B-cells. However, a definitive normal cellular counterpart cannot be attributed on the basis of the available data. We discuss the functional characteristics required for a cell to be logically considered to be the normal counterpart of CLL B-cells.

Somatostatin Improved B Cells Mature in Macaques during Intestinal Ischemia-Reperfusion

AIMS

Intestinal ischemia-reperfusion has been taken as an important pathophysiological process for multiple organ dysfunctions in critical patients. Recent studies reported that dual expression programs of the B cells receptors and Toll-like receptors on B-lymphocytes permit these ubiquitous cells to integrate both adaptive and innate immune functions. Our previous studies found that somatostatin inhibited the intestinal inflammatory injury after ischemia-reperfusion in macaques. However, the changes of B cells and the effects of somatostatin on B cells after intestinal ischemia-reperfusion were unclear.

METHODS

15 macaques were divided into control, intestinal ischemia-reperfusion and somatostatin pretreatment groups. Immunohistochemistry was performed to identify the distributions of adaptive and innate immunity markers in the iliac mucosa. Hmy2.cir B lymphoblastoid cell line was cultured in vitro study. Enzyme-linked immunosorbent assay was used to measure IgM, IL-6 and SIgA, and the expressions of B cells transcription factors, PAX-5 and BLIMP-1, were detected by Western blotting.

RESULTS

B2 lymphocytes in normal Peyer's patches were presented the phenotype of PAX-5+CD20+CD5-. Ischemia-reperfusion increased the numbers and sizes of Peyer's patches but with PAX-5+CD20-CD5- B cells, an unmatured set of B cells. Somatostatin partly kept the phenotype of mature B cells during ischemia-reperfusion. The innate immunity of B cells was inhibited whereas the adaptive immunity was increased in the intestinal mucosa in the somatostatin group, compared to the ischemia-reperfusion group. In vitro, somatostatin significantly inhibited IL-6 and promoted IgM by increasing the expression of both PAX-5 and BLIMP-1 in the proinflammatory condition.

CONCLUSION

Intestinal ischemia-reperfusion resulted in the proliferation of unmatured B cells which were involved in the augmentation of innate immunity. Somatostatin, with a bi-directional regulation function on innate as well as adaptive immunity of B cells, greatly improved B cells mature in macaques during ischemia-reperfusion. Preventive supplements of somatostatin may greatly limit intestinal injury and bacterial translocation during ischemia-reperfusion.

Immunology of normal pregnancy

Since Medawar's initial contemplations in 1953 on the mechanisms of immune evasion allowing for the survival of the allogeneic conceptus in an immunologically competent mother, physicians and immunologists alike have struggled to understand the immunological paradox of pregnancy. Ultimately, our attempts to define the immunology of normal pregnancy have broadened our appreciation of the myriad mechanisms at play that enable the promotion of implantation and maintenance of pregnancy. In this review, we summarise what is known regarding the immunology of normal pregnancy, with special emphasis on the relation to common disorders of pregnancy.

Overproduction of corticotropin-releasing hormone blocks germinal center formation: role of corticosterone and impaired follicular dendritic cell networks

Corticotropin-releasing hormone (CRH) is a central mediator in the response to stress, coordinating behavioral, autonomic and neuroendocrine activation. CRH overproduction is implicated in several affective disorders, including major depression, panic-anxiety disorder and anorexia--diseases also associated with altered immune function. We investigated the link between CRH overdrive and immune function using CRH transgenic mice. Following immunization, CRH transgenic mice fail to form germinal centers; chronic glucocorticoid administration recapitulates this effect in wild-type mice. Regulation of germinal centers by glucocorticoids appears to be mediated, in part, through effects on follicular dendritic cells (FDC), providing a novel mechanism by which CRH dysregulation may significantly impair humoral immune responses.

Apoptosis in primary lymphoid organs with aging

Age-associated changes in the immune system are responsible for an increased likelihood of infection, autoimmune diseases, and cancer in the elderly. Immunosenescence is characterized by reduced levels of the peripheral naive T cell pool derived from thymus and the loss of immature B lineage cells in the bone marrow. Primary lymphoid organs, i.e., bone marrow and thymus, exhibit a loss of cellularity with age, which is especially dramatic in the thymus. A summary of major changes associated with aging in primary lymphoid organs is described in this article. The participation of apoptosis in cell loss in the immune system, a change associated with age, as well as a description of molecular machinery involved, is presented. Finally, the involvement of different hormonal and non-hormonal agents in counteracting apoptosis in thymus and bone marrow during aging is explained. Here, we underlie the important role of glucocorticoids as immunodepressors and melatonin as an immunostimulatory agent.

Bruton's tyrosine kinase cooperates with the B cell linker protein SLP-65 as a tumor suppressor in Pre-B cells

Expression of the pre-B cell receptor (pre-BCR) leads to activation of the adaptor molecule SLP-65 and the cytoplasmic kinase Btk. Mice deficient for one of these signaling proteins have an incomplete block in B cell development at the stage of large cycling pre-BCR+CD43+ pre-B cells. Our recent findings of defective SLP-65 expression in approximately 50% of childhood pre-B acute lymphoblastic leukemias and spontaneous pre-B cell lymphoma development in SLP-65-/- mice demonstrate that SLP-65 acts as a tumor suppressor. To investigate cooperation between Btk and SLP-65, we characterized the pre-B cell compartment in single and double mutant mice, and found that the two proteins have a synergistic role in the developmental progression of large cycling into small resting pre-B cells. We show that Btk/SLP-65 double mutant mice have a dramatically increased pre-B cell tumor incidence ( approximately 75% at 16 wk of age), as compared with SLP-65 single deficient mice (<10%). These findings demonstrate that Btk cooperates with SLP-65 as a tumor suppressor in pre-B cells. Furthermore, transgenic low-level expression of a constitutive active form of Btk, the E41K-Y223F mutant, prevented tumor formation in Btk/SLP-65 double mutant mice, indicating that constitutive active Btk can substitute for SLP-65 as a tumor suppressor.

Long-term kinetics of adult human antibody repertoires

In healthy humans, antibody repertoires change during ontogeny and senescence. The dynamics of antibody repertoires among adults over a longer period of time in one and the same individual has, however, not been extensively studied. In this study we analysed peripheral blood samples from five healthy adults, taken over a period of 10 weeks and once 9 years later. A competitive, quantitative polymerase chain reaction (PCR) was developed to investigate short and long-term variations in VH gene family repertoires. Serum antibody levels to common self and non-self antigens were determined in samples taken at the same time-points as the cell samples to analyse possible correlations between molecular and serological expression profiles. We found a high degree of stability in the VH gene family repertoire over time as well as between individuals with a Caucasian background. A specific change in the usage of primarily the VH3 and VH5 gene families was observed in one individual at one time-point. The deviating pattern resembled the VH gene family utilization pattern observed in naturally activated B lymphocytes. The fluctuations in VH3 and VH5 gene family expression correlated with the presence of rheumatoid factor in serum. We discuss the possible influence of polyclonal, transient stimulation of B cells on VH gene repertoires, as measured in circulating B cells.

Bone marrow stromal cells mediate androgenic suppression of B lymphocyte development

Castration of normal male mice induces expansion of the bone marrow B cell population, an effect that can be reversed by androgen replacement. We employed in vitro cultures and two in vivo models to investigate whether androgens exert these effects directly on marrow lymphoid precursors or whether actions on marrow stromal elements are required. Immature B cells from normal mouse bone marrow were not responsive to the suppressive effect of androgens unless they were cocultured with marrow stromal cells or with supernatants from androgen-treated stromal cells, suggesting that the androgen effects are exerted through marrow stromal elements by production of a diffusible mediator. Further experiments revealed that bone marrow stromal cells produced TGF-beta in response to dihydrotestosterone (DHT), and neutralization of TGF-beta in the DHT-treated stromal cells reversed the suppressive effects. The stromal cell requirement for androgen-mediated effects was confirmed in vivo by experiments using chimeric animals created by bone marrow transplantation in which androgen receptor expression was restricted to either the stromal or lymphoid cells of the bone marrow. Androgens only affected B cell development in chimeric mice with androgen-sensitive stromal cells. These experiments suggest that effects of androgens on developing B cells are mediated through androgen receptors in bone marrow stromal cells. TGF-beta is a candidate mediator for these hormonal effects.

A distinct role for apoptosis in the changes in lymphopoiesis and myelopoiesis created by deficiencies in zinc

Reduced numbers of lymphocytes in the peripheral immune system appeared to be a significant cause of the loss in host defense capacity in humans and animals that are zinc deficient (ZD). A series of studies verified that ZD substantially reduced the lymphocyte compartment of both the marrow and thymus in young adult mice, with large losses noted among the pre-B and pre-T cells. Suboptimal nutriture along with chronic production of glucocorticoids generated during ZD had accelerated apoptosis among these precursor lymphocytes two- to threefold. Thus, the primary cause of the lymphopenia created by ZD was reduced production of lymphocytes and heightened cell death among precursor cells. The data will also show that myelopoiesis in the marrow was protected and enhanced numbers of myeloid progenitor cells were found in S and G2/M. Thus, as zinc became limiting the second line of defense appeared to be down-regulated via reduction of lymphopoiesis while cells of the myeloid lineage were protected to maintain the first line of defense that provides innate immunity. This may represent an important adaptation of the immune system to suboptimal nutriture that deserves further exploration.

Annexin V binds to positively selected B cells

Recombinant annexin V (rAnV) has been used in flow cytometry to identify cells undergoing apoptosis, based on its ability to bind to phosphatidylserine, a negatively charged lipid normally restricted to the cytoplasmic face of the plasma membrane but externalized early during apoptosis. When we stained murine bone marrow (BM) cells with fluorescently labeled rAnV, we found that a surprisingly large fraction of BM B cells bearing selectable transgenic Ag receptors bind significant amounts of rAnV, but that these cells are not apoptotic. Here, we show that binding of rAnV to developing B cells in normal mice correlates with B cell receptor-dependent selection events at several stages of development within both B-1 and B-2 cell subsets. In fact, nearly all B-1 B cells and splenic marginal zone B cells bind rAnV, suggesting that the externalization of phosphatidylserine occurs once mature B cells are selected through BCR-mediated signaling. However, this plasma membrane alteration is apparently not shared by all lymphocytes, because we did not find a parallel population of rAnV-binding viable T cells in vivo in normal or TCR transgenic mice. We also show that BM stromal cell lines can influence the extent of rAnV binding by viable BM B cells during coculture in vitro. We suggest that rAnV detects a potentially important membrane alteration that occurs as B cells develop in the BM and are readied for export to the peripheral lymphoid organs and again among mature B cells recruited to the marginal zone or the B-1 compartment.

The dynamic link between the integrity of the immune system and zinc status

The results of more than three decades of work indicate that zinc deficiency rapidly diminishes antibody- and cell-mediated responses in both humans and animals. The moderate deficiencies in zinc noted in sickle cell anemia, renal disease, chronic gastrointestinal disorders and acrodermatitis enteropathica; subjects with human immunodeficiency virus; children with diarrhea; and elderly persons can greatly alter host defense systems, leading to increases in opportunistic infections and mortality rates. Conversely, short periods of zinc supplementation substantially improve immune defense in individuals with these diseases. Mouse models demonstrate that 30 d of suboptimal intake of zinc can lead to 30-80% losses in defense capacity. Collectively, the data clearly demonstrate that immune integrity is tightly linked to zinc status. Lymphopenia and thymic atrophy, which were the early hallmarks of zinc deficiency, are now known to be due to high losses of precursor T and B cells in the bone marrow. This ultimately leads to lymphopenia or a failure to replenish the lymphocytic system. Glucocorticoid-mediated apoptosis induced by zinc deficiency causes down-regulation of lymphopoiesis. Indeed, zinc itself can modulate death processes in precursor lymphocytes. Finally, there is substantial evidence that zinc supplementation may well reduce the impact of many of the aforementioned diseases by preventing the dismantling of the immune system. The latter represents an important area for research.

Annexin V binds to viable B cells and colocalizes with a marker of lipid rafts upon B cell receptor activation

Recombinant annexin V (rAnV) has been used to identify apoptotic cells based on its ability to bind phosphatidylserine (PS), a lipid normally restricted to the cytoplasmic face of the plasma membrane, but externalized early during apoptosis. However, this association of rAnV binding and apoptosis is not an obligatory one. We demonstrate that rAnV binds to a large fraction of murine B cells bearing selectable Ag receptors despite the fact that these cells are not apoptotic. Phosphatidylserine, which is uniformly distributed on resting B cells, is mobilized to co-cap with IgM on anti-IgM-treated B cells and to colocalize with GM1, a marker of lipid rafts. Cross-linking PS before anti-IgM treatment sequesters this lipid and alters signaling through IgM. Thus, PS exposed on the majority of B cells in vivo does not reflect early apoptosis, but, instead, plays a role in receptor-mediated signaling events.

Effects of in utero alcohol exposure on B cell development in neonatal spleen and bone marrow

The effects of in utero alcohol exposure on neonatal lymphopoiesis were examined in a murine model of fetal alcohol syndrome. At birth, both immature and mature B cells were decreased in the spleens of neonatal animals and these subpopulations of B cells did not recover to normal levels until 3-4 weeks of life. Pre-B cells and total B cells were decreased as well in the bone marrow of ethanol-exposed animals. By 3-4 weeks of life, the number of B cells in the bone marrow recovered to normal levels, but the pre-B cells remained below normal levels through 5 weeks of age. Furthermore, a recently described early B cell progenitor was reduced in frequency in ethanol-exposed neonates. Together, these data suggest that in utero exposure to ethanol can result in abnormalities in B cell development that may initiate at an early stage of B cell development.

Somatic Mutation in the Neonatal Mouse

Several mechanisms that diversify the adult immune repertoire, such as terminal deoxynucleotidyl transferase-dependent N region addition, are not available to the neonatal mouse. One important process that contributes to protective immunity in the adult is somatic mutation, which plays a major role in the generation of high affinity memory B cells. It is not clear whether B cells in the neonatal mouse can activate the somatic mutation machinery. To investigate this, we immunized neonates with poly(l-Tyr,l-Glu)-poly-d, l-Ala–poly-l-Lys complexed with methylated BSA, or (4-hydroxy-3-nitrophenyl)acetyl coupled to chicken γ-globulin. Eight to fourteen days after priming, V(D)J rearrangements of known VH genes (VHSM7 family) were screened for mutations using a temperature-melt hybridization assay and oligonucleotide probes specific for complementarity-determining regions I and II; possible mutations were confirmed by sequence analysis. More mutations per sequence were found in heavy chains from neonates immunized with (4-hydroxy-3-nitrophenyl)acetyl coupled to chicken γ-globulin than in those from neonates immunized with poly(l-Tyr, l-Glu)-poly-d,l-Ala-poly-l-Lys complexed with methylated BSA. Mutations were found in heavy chains lacking N regions, suggesting that B cells of the putative fetal lineage can somatically mutate and diversify an initially limited repertoire. Since neonates immunized as early as 1 or 2 days after birth had mutations, the somatic mutation machinery can be activated soon after birth, suggesting that early vaccination should result in affinity maturation and protective immunity in the neonate.

B-cell reconstitution and xenoreactive anti-pig natural antibody production in severe combined immunodeficient mice reconstituted with immunocompetent B cells from varying sources

BACKGROUND

Little is known about the B-cell subsets that produce xenoreactive natural antibodies (NAb). This study was undertaken to investigate the potential role of varying B-cell populations in anti-pig NAb production in mice.

METHODS

Severe combined immunodeficient (scid) mice were reconstituted with bone marrow or splenic or peritoneal B cells from immunocompetent mice. B-cell reconstitution and anti-pig NAb were evaluated by flow cytometric analysis.

RESULTS

Adult marrow failed to reconstitute normal numbers of CD5+ B1a cells, but fully reconstituted CD5- Mac1- B2 and CD5- Mac1+ B1b cell populations in scid mice. Recipients of peritoneal B cells showed poor reconstitution of B2 cells, and an overshoot of B1 cells in the peritoneal cavity. Although B2 cells predominate in the adult spleen, splenic B cells from immunocompetent mice preferentially reconstituted B cells, including B1 cells, in the peritoneal cavity, but did not reconstitute splenic B2 cells. Therefore, neither adult marrow, splenocytes nor peritoneal cells can fully reconstitute scid mice with all B-cell subpopulations. Nevertheless, serum anti-pig NAb in marrow-reconstituted mice recovered to normal levels by 3 weeks, and were maintained for at least 30 weeks. Serum NAb in scid mice receiving peritoneal B cells reached normal levels by 4-7 weeks after transfer. However, NAb in sera of scid mice receiving splenic B cells took longer (>25 weeks) to reach normal levels.

CONCLUSIONS

These results indicate that adult marrow-derived B cells can efficiently produce anti-pig NAb, and that peritoneal B cells have greater NAb-producing ability than splenic B cells or their immediate progeny.

Molecular and immunophenotypical characterization of a feline immunodeficiency virus (FIV)-associated lymphoma: a direct role for FIV in B-lymphocyte transformation?

We describe the histopathological, immunohistochemical, and molecular characterization of a lymphoma arising in a 7-year-old cat following experimental infection with feline immunodeficiency virus (FIV). The tumor was high grade and of B-cell lineage. The transformed cell had an immature phenotype (CD79a+, CD79b-, CD21-, immunoglobulin heavy and light chain negative), confirmed by antigen receptor gene analysis, which showed germ line configuration. Single-copy, clonally integrated FIV provirus was detected in tumor genomic DNA. FIV p24 antigen was not detected in tumor cells by immunostaining. This study provides the first evidence that the feline lentivirus may play a direct role in cell transformation under certain circumstances.

Age-related impaired affinity maturation and differential D-JH gene usage in human VH6-expressing B lymphocytes from healthy individuals

To elucidate the basic molecular events underlying humoral immunity during ontogeny and senescence, we analyzed a panel of 179 polymerase chain reaction-derived VH6-D-JH rearrangements from cord blood, peripheral blood, and spleen. Nucleotide sequence analysis of the CDR3 region shows that there is a difference in D and JH gene usage in functional rearrangements between lymphocytes from peripheral blood and spleen. Analysis of the VH6 gene shows that the mutational frequencies rise from 0.81% in cord blood to 1.96% in peripheral blood lymphocytes derived from young adults, and decrease to 0.80% in samples from individuals older than 50 years. The number of rearrangements carrying mutations follows a similar pattern: 22% in cord blood, 73% in the age group 20-49 years, and 57% in the age group over 50 years. The mutational frequencies among the mutated genes are, however, similar for cord blood and young adults, 2.76% and 2.51%, respectively, and 1.3% in older adults. These data show an age-related impaired affinity maturation which might relate to the decrease in immunological responsiveness among the elderly.

Ontogeny of neuroepithelial bodies: correlations with mitogenesis and innervation

This paper summarizes current knowledge and advances speculation about the formation of the neuroendocrine system of mammalian lungs (comprising uninnervated solitary and clustered small-granule cells and innervated neuroepithelial bodies). It relates the initial appearance of neuroendocrine cells to regulation of mitotic activity in the epithelium during the development of the lung and pays special attention to the later in growth of nerves that converts some of them into neuroepithelial bodies, structures considered ideally adapted to function as chemoreceptors. A few original observations from ongoing immunohistochemical, electron microscopic, and analytical studies have been included here and there to point the discussion. The neuroendocrine cells are derived from undifferentiated precursors present in the endodermal pulmonary epithelium. At an early pseudoglandular stage of lung development these precursors begin to differentiate into neuroendocrine small-granule cells, commencing in the larynx and upper trachea, and expanding centrifugally into pulmonary airways almost as rapidly as these are laid down. Subsequently many of the intrapulmonary small-granule cell clusters become innervated. This event, the delayed appearance of small-granule cells synthesizing other than the dominant peptides and amines (calcitonin gene-related peptide and serotonin in rodents, gastrin-releasing peptide and serotonin in human beings), and other regional adjustments yield the population distribution present in the lungs of adults. Neuroendocrine cell precursors normally differentiate into typical serotonin- or peptide-synthesizing small-granule cells without requiring direct contact by nerves, and dissociated cells from a previously innervated population continue to exhibit physiological characteristics of oxygen sensors despite the loss of contact with nerves. Development of the innervation occurs in stages. Small-granule cell clusters are reached first by ganglion cells derived from pulmonary neuroblasts and later on by processes of extrinsic sensory nerves. The latter not only convey information to the central nervous system but also serve in a variety of ways to extend the neuroepithelial bodies' sphere of influence within the lung itself.

Correction of the X-linked immunodeficiency phenotype by transgenic expression of human Bruton tyrosine kinase under the control of the class II major histocompatibility complex Ea locus control region

Bruton tyrosine kinase (Btk) is essential for the development of pre-B cells to mature B cell stages. Btk-deficient mice manifest an X-linked immunodeficiency (xid) defect characterized by a reduction of peripheral IgMlow IgDhigh B cells, a lack of peritoneal CD5+ B cells, low serum levels of IgM and IgG3, and impaired responses to T cell independent type II (TI-II) antigens. We have generated transgenic mice in which expression of the human Btk gene is driven by the murine class II major histocompatibility complex Ea gene locus control region, which provides gene expression from the pre-B cell stage onwards. When these transgenic mice were mated onto a Btk- background, correction of the xid B cell defects was observed: B cells differentiated to mature IgMlowIgDhigh stages, peritoneal CD5+ B cells were present, and serum Ig levels and in vivo responses to TI-II antigens were in the normal ranges. A comparable rescue by transgenic Btk expression was also observed in heterozygous Btk+/- female mice in those B-lineage cells that were Btk-deficient as a result of X chromosome inactivation. These findings indicate that the Btk- phenotype in the mouse can be corrected by expression of human Btk from the pre-B cell stage onwards.

B1 and B2 cells differ in their potential to switch immunoglobulin isotype

The ability of purified B1a (Ly-1 B) and B2 cells to switch immunoglobulin isotype was assessed by limiting dilution analysis in two in vitro culture systems. When stimulated in the presence of interleukins-4 and -5 by either lipopolysaccharide or CD40 ligand, the frequency of IgG1 precursors in the B1a population was at most one third that of IgM precursors. In B2 cells, however, the frequency of IgG1 precursors was up to seven times that of IgM precursors. B1a cells were shown to respond to interleukin-4 by virtue of up-regulating major histocompatibility complex class II expression when exposed to the cytokine, precluding non-responsiveness as a reason for not switching to IgG1. Indeed, interleukin-4 was found to specifically induce transcription of the germ-line IgG1 constant region locus in B1a cells as it did in B2 cells. Collectively these results suggest that the ability of B1 cells to respond to isotype switch commitment factors such as interleukin-4 may be secondary to the production of IgM by these cells.