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PubMed2004

A protective role for innate immunity in systemic lupus erythematosus.

Clinical and genetic studies in humans and animal models indicate a crucial protective role for the complement system in systemic lupus erythematosus (SLE). This presents a paradox because the complement system is considered to be an important mediator of the inflammation that is observed in patients with SLE. One current view is that complement provides protection by facilitating the rapid removal of apoptotic debris to circumvent an autoimmune response. In this Opinion article, I discuss an alternative model in which complement - together with other components of the innate immune system - participates in the 'presentation' of SLE-inducing self-antigens to developing B cells. In this way, the complement system and innate immunity protect against responses to SLE (self) antigens by enhancing the elimination of self-reactive lymphocytes.

Animals↗

PubMed1986

Human skeletal growth factor stimulates collagen synthesis and inhibits proliferation in a clonal osteoblast cell line (MC3T3-E1).

Human skeletal growth factor (hSGF), an 11-kD polypeptide purified from human bone, has been proposed to be a local regulator of bone formation. To investigate the underlying cellular mechanisms in an in vitro model system, we examined the effects of hSGF on proliferation and collagen synthesis in cells of the clonal osteoblast cell line MC3T3-E1. This line was isolated from newborn mouse calvarial cells and retains many characteristics of mature osteoblasts (Sudo, H., et al., (1984) J. Cell Biol. 96:191). A 14-hr treatment with hSGF increased noncollagenous protein synthesis to 215% of unstimulated controls and increased collagen synthesis to 630% of controls as determined by [3H]proline incorporation and high-pressure liquid chromatographic separation of [3H]proline and [3H]hydroxyproline in acid hydrolysates of trichloroacetic acid-insoluble protein. HSGF did not increase cell number over a 48-hr period and caused a reversible inhibition of DNA synthesis. Half-maximal hSGF concentration for stimulation of [3H]proline incorporation and inhibition of [3H]thymidine incorporation was 100 ng/ml. HSGF also inhibited DNA synthesis in cells stimulated by serum. In contrast, hSGF stimulated both collagen synthesis and DNA synthesis in primary cultures of chick embryo bone cells, which may be developmentally less mature than MC3T3-E1 cells. The results suggest that hSGF directly stimulated mature osteoblast matrix synthetic activity and that hSGF has differential effects on proliferation of osteoblast progenitor cells and mature osteoblasts.

Animals↗

PubMed1998

Genetic instability in radiation-induced leukaemias: mouse models.

PURPOSE: Genetic instability plays a major role in multi-stage carcinogenesis. Ionizing radiation induces delayed genetic instability which can be transmitted to the clonal offspring of the irradiated cell, so it is of considerable importance to determine whether radiation-induced genetic instability contributes to radiation-leukaemogenesis. RESULTS: The experimental data obtained using radiation-induced leukaemias in mouse models were reviewed, and an attempt was made to distinguish between the instability detectable in de novo cancers and that which is associated with ionising radiation. Genetic lesions identified in mouse leukaemias include non-clonal chromosomal aberrations, loss of heterozygosity, and minisatellite/microsatellite mutations. CONCLUSIONS: Studies of mouse radiation-induced leukaemias have detected evidence of genetic instability. However, with few exceptions, most of this instability was also observed during de novo multi-stage carcinogenesis. This raises the possibility that radiation induces ongoing genetic instability that is functionally indistinguishable to that implicated in de novo tumour progression.

Animals↗

PubMedDate not supplied

Effective immunotherapy of cancer in MUC1-transgenic mice using clonal cytotoxic T lymphocytes directed against an immunodominant MUC1 epitope.

The tumor-associated autoantigen MUCI is intensively studied as a potential target for antigen-specific immunotherapy of cancer. Previous reports concerning experiments in preclinical murine tumor models have provided evidence supporting the feasibility of this approach. However, such studies have not been performed with clonal cytotoxic T lymphocyte populations displaying a highly defined MUC1 specificity. The authors demonstrate that the immunodominant MUC1-specific cytotoxic T lymphocyte response in C57BL/6 mice is directed against an H-2Kb-restricted epitope, MUC1(19-27), which is derived from the N-terminal signal sequence of the MUC1 protein. Processing of this epitope was independent of transporter of antigen presentation and proteasome function. Importantly, successful immunotherapy of MUC1-overexpressing tumors in MUC1-transgenic mice was not accompanied by damage to normal somatic MUC1-positive tissues, even when this involved the infusion of large numbers of clonal cytotoxic T lymphocyte that recognized the immunodominant MUC1 epitope. Although the risk for autoimmune pathology is limited, data indicate that immune tolerance in MUC1-positive subjects restricts the breadth of the MUC1-specific cytotoxic T lymphocyte repertoire that is available for recruitment to immunotherapeutic antitumor responses.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

A developmental model of neuroblastoma: differentiating stroma-poor tumors' progress along an extra-adrenal chromaffin lineage.

The prognosis of children with neuroblastoma (NB) is dependent upon the patient's age at diagnosis, the location of the primary tumor, and histologic tumor cell differentiation. These characteristics, as well as the presumption that NB results from clonal expansion of primitive cells involved in sympathetic nervous system (SNS) development, predict that a model of tumorigenesis based upon normal fetal SNS histogenesis might indicate tumor progenitor status and define biologic and clinical behavior. Immunohistochemistry and in situ hybridization were used to examine a panel of marker gene products predicted or shown to be expressed during SNS development in the normal human fetal SNS from 8 to 24 weeks' gestational age. A similar analysis was performed in a selection of clinical NB tumors, and the results were compared. In a subset of differentiating, often extra-adrenal NB tumors in patients who frequently had a favorable outcome; advancing morphologic tumor cell differentiation spatially paralleled an advancing fetal extra-adrenal chromaffin marker gene expression phenotype (ie, increasing TrkA, TrkC, TH, IGF-2, and neuron-specific enolase expression but a lack of phenylethanolamine N-methyltransferase expression). In these tumors, expression of gene products associated with normal fetal sympathetic ganglionic differentiation (ie, Bcl-2, HNK-1, and neuropeptide Y) was lost with morphologic tumor cell differentiation. In contrast, undifferentiated tumors, the majority of which were high stage, adrenal in origin, and prognostically unfavorable, displayed marker expression characteristics mirroring that of an early fetal ganglionic lineage. Thus, we show that morphologic differentiation in stroma-poor NB tumors, long held as an important prognostic feature in tumor grading systems, often corresponds to an extra-adrenal chromaffin rather than a ganglion cell or adrenal medullary chromaffin phenotype. Understanding the biology of extra-adrenal chromaffin tissues may provide an explanation for the clinically less aggressive nature of differentiating NB tumors and suggest potential mechanisms for spontaneous regression and/or treatment response.

Biomarkers, Tumor↗

PubMed2006

Genetic variability and adaptive evolution in parthenogenetic root-knot nematodes.

Root-knot nematodes (RKN) of the genus Meloidogyne are biotrophic plant parasites of major agricultural importance, which exhibit very variable modes of reproduction, from classical amphimixis to mitotic parthenogenesis. This review focuses on those RKN species that reproduce exclusively by mitotic parthenogenesis (apomixis), in contrast to those that have meiotic/amphimitic events in their life cycle. Although populations of clonal organisms are often represented as being ecologically isolated and evolutionary inert, a considerable volume of literature provides evidence that asexual RKN are neither: they are widely distributed, extremely polyphagous, and amenable to selection and adaptive variation. The ancestors of the genus are unknown, but it is assumed that the parthenogenetic RKN have evolved from amphimictic species through hybridization and subsequent aneuploidization and polyploidization events. Molecular studies have indeed confirmed that the phylogenetic divergence between meiotic and mitotic RKN lineages occurred early, and have revealed an unexpected level of clonal diversity among populations within apomictic species. Laboratory experiments have shown that asexual RKN can rapidly adapt to new environmental constraints (eg host resistance), although with some fitness costs. Lastly, the molecular and chromosomal mechanisms that could contribute to genome plasticity leading to persistent genetic variation and adaptive evolution in apomictic RKN are discussed. It is concluded that RKN provide an excellent model system in which to study the dynamic nature and adaptive potential of clonal genomes.

Adaptation, Physiological↗

PubMed1992

Autoimmune tolerance and type 1 (insulin-dependent) diabetes mellitus.

The autoimmune process that results in Type 1 (insulin-dependent) diabetes mellitus may be viewed as a failure to develop or maintain tolerance to self-antigens expressed in the islets of Langerhans. During T-cell development in the thymus, cells that are reactive with self antigens encountered there may undergo clonal deletion or, as more recently described, clonal anergy which effectively removes these cells from the pool of mature antigen reactive T cells. For antigens not found in the thymus, tolerance to self antigens is more complex and may depend on site of antigen expression, ambient concentrations of lymphokines, and availability of antigen-presenting cells that can deliver co-stimulatory signals. Transgenic mice in which the majority of T cells express T-cell receptors against "self" antigens or in which expression of antigens is targeted to peripheral tissues have proven useful for studies of tolerance in both T- and B-cell compartments. In general, T-cell reactivity against foreign antigen expressed on Beta cells does not occur because of the failure to activate T cells reactive with the antigen, termed clonal ignorance. This may be broken with, for example, viral infection or cytokines. In one transgenic model, dendritic cells that surround the islets of Langerhans have been shown to be responsible for presentation of islet antigens to the immune system. B-cell tolerance can also involve mechanisms of clonal deletion or clonal anergy similar to that occurring with T cells. In addition, a mechanism for changing the affinity of the B-cell antigen receptor termed "receptor editing" has been described, which may play an important role in diversifying the B-cell repertoire while removing self-reactive cells. Tolerance to antigens may also be inducible. For example, monoclonal antibodies against T-cell epitopes may induce antigen-specific tolerance that is transferable to other animals, and MHC blocking peptides which can inhibit T-cell responses that are restricted by disease associated MHC molecules. In conclusion, although several possible triggers and mechanisms of autoimmune diabetes can be envisioned, none can be excluded by existing data. However, advances in understanding mechanisms of tolerance to islet and other self antigens suggest potentially useful therapeutic approaches to arresting the autoimmune response.

Animals↗

PubMed2004

Assessment of clonal relationships in ipsilateral and bilateral multiple breast carcinomas by comparative genomic hybridisation and hierarchical clustering analysis.

The issue of whether multiple, ipsilateral or bilateral, breast carcinomas represent multiple primary tumours or dissemination of a single carcinomatous process has been difficult to resolve, especially for individual patients. We have addressed the problem by comparative genomic hybridisation analysis of 26 tumours from 12 breast cancer patients with multiple ipsilateral and/or bilateral carcinoma lesions. Genomic imbalances were detected in 25 of the 26 (96%) tumours. Using the genomic imbalances detected in these 26 lesions as well as those previously found by us in an independent series of 35 unifocal breast carcinomas, we compared a probabilistic model for likelihood of independence with unsupervised hierarchical clustering methodologies to determine the clonal relatedness of multiple tumours in breast cancer patients. We conclude that CGH analysis of multiple breast carcinomas followed by unsupervised hierarchical clustering of the genomic imbalances is more reliable than previous criteria to determine the tumours' clonal relationship in individual patients, that most ipsilateral breast carcinomas arise through intramammary spreading of a single breast cancer, and that most patients with bilateral breast carcinomas have two different diseases.

Adult↗

PubMed2004

CD24 controls expansion and persistence of autoreactive T cells in the central nervous system during experimental autoimmune encephalomyelitis.

In the development of experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis (MS), autoreactive T cells must be activated and clonally expand in the lymphoid organs, and then migrate into the central nervous system (CNS) where they undergo further activation. It is unclear whether the autoreactive T cells further expand in the CNS and if so, what interactions are required for this process. We have demonstrated previously that expression by the host cells of the heat-stable antigen (CD24), which was recently identified as a genetic modifier for MS, is essential for their susceptibility to EAE. Here we show that CD24 is essential for local clonal expansion and persistence of T cells after their migration into the CNS, and that expression of CD24 on either hematopoietic cells or nonhematopoietic antigen-presenting cells in the recipient is sufficient to confer susceptibility to EAE.

Adoptive Transfer↗

PubMed2006

Mitochondrial damages and the regulation of insulin secretion.

Pancreatic beta-cells are able to respond to nutrients, principally glucose, as the primary stimulus for insulin exocytosis. This unique feature requires translation of metabolic substrates into intracellular messengers recognized by the exocytotic machinery. Central to this signal transduction mechanism, mitochondria integrate and generate metabolic signals, thereby coupling glucose recognition with insulin secretion. In response to a glucose rise, nucleotides and metabolites are generated by mitochondria and participate, together with cytosolic Ca2+, in the stimulation of insulin exocytosis. Mitochondrial defects, such as mutations and ROS (reactive oxygen species) production, might be associated with beta-cell failure in the course of diabetes. mtDNA (mitochondrial DNA) mutation A3243G is associated with MIDD (mitochondrial inherited diabetes and deafness). A common hypothesis to explain the link between the genotype and the phenotype is that the mutation might impair mitochondrial metabolism expressly required for beta-cell functions, although this assumption lacks direct demonstration. mtDNA-deficient cellular models are glucose-unresponsive and are defective in mitochondrial function. Recently, we used clonal cytosolic hybrid cells (namely cybrids) harbouring mitochondria derived from MIDD patients. Compared with control mtDNA from the same patient, the A3243G mutation markedly modified metabolic pathways. Moreover, cybrid cells carrying patient-derived mutant mtDNA exhibited deranged cell Ca2+ handling and elevated ROS under metabolic stress. In animal models, transgenic mice lacking expression of the mitochondrial genome specifically in beta-cells are diabetic and their islets are incable of releasing insulin in response to glucose. These various models demonstrate the fragility of nutrient-stimulated insulin secretion, caused primarily by defective mitochondrial function.

DNA, Mitochondrial↗

PubMed1999

A stochastic model of temporally regulated generation of oligodendrocytes in cell culture.

The results of our previous analyses suggest that O-2A progenitor cells become competent for differentiation in vitro after they complete a certain number of critical mitotic cycles. The number of critical cycles varies from clone to clone and should be thought of as a random variable. We propose an approach to the analysis of oligodendrocyte generation in vitro based on a stochastic model allowing for an arbitrary distribution of this random variable with a finite support. When applied to experimental data on clonal growth and differentiation of purified O-2A progenitor cells obtained from optic nerves of 1 and 7 day-old rats, the model provides a good quantitative description not only of the first two moments (mean and variance) of the number of O-2A progenitor cells and oligodendrocytes at different times after the start of experiment, but of the corresponding distributions as well. As our estimates show, there are scarcely any O-2A progenitor cells that divide in vitro more than twice before they acquire the competence for differentiation. Those O-2A cells that have undergone the critical divisions differentiate into an oligodendrocyte in each of the subsequent mitotic cycles with a certain probability. We give estimates of this probability for O-2A cells under different growth conditions. Our analysis suggests that the effect of thyroid hormone is twofold: it reduces the mean duration of the mitotic cycle for progenitor cells, and it increases the probability of their transformation into oligodendrocytes.

Animals↗

PubMed2026

Liquid biopsies reveal dual compartments of cancer risk from tumor and host-derived mutations.

MOTIVATION: Circulating tumor DNA (ctDNA) and clonal hematopoiesis of indeterminate potential (CHIP) are two biologically distinct sources of somatic mutations detectable in blood. While ctDNA captures tumor-intrinsic alterations, CHIP arises from age-related hematopoietic clones and is often considered background noise. Here, we conduct a large-scale, tumor-type-resolved analysis of over 9000 patients with CHIP data and 1500 patients with ctDNA data across solid tumors profiled at Memorial Sloan Kettering Cancer Center. RESULTS: Our results reveal that CHIP and ctDNA mutations exhibit non-overlapping, clinically meaningful signals. CHIP mutations, particularly in DNA damage response and epigenetic regulators (e.g. PPM1D, CHEK2, ATM, TP53, ASXL1), are associated with worse overall survival, increased metastatic potential, and site-specific dissemination. ctDNA mutations in canonical oncogenic drivers (e.g. TP53, EGFR, KRAS, STK11) reflect tumor aggressiveness and correlate with poor prognosis and metastasis across multiple cancer types. Joint modeling in lung adenocarcinoma confirms the independent prognostic contributions of both compartments. Additionally, longitudinal clonal analysis links specific CHIP mutations to the emergence of hematologic malignancies under therapeutic pressure. These findings support a dual-compartment model of liquid biopsy, in which tumor- and host-derived mutations jointly inform on cancer risk, progression, and metastatic behavior. Integrating both compartments may enhance the clinical utility of blood-based biomarkers in oncology. AVAILABILITY: All genomic and clinical data used in this study are available through cBioPortal. Summarized outputs and processed results tables are provided in Supplementary Data.

Humans↗

PubMed2006

Fisher waves and front roughening in a two-species invasion model with preemptive competition.

We study front propagation when an invading species competes with a resident; we assume nearest-neighbor preemptive competition for resources in an individual-based, two-dimensional lattice model. The asymptotic front velocity exhibits an effective power-law dependence on the difference between the two species' clonal propagation rates (key ecological parameters). The mean-field approximation behaves similarly, but the power law's exponent slightly differs from the individual-based model's result. We also study roughening of the front, using the framework of nonequilibrium interface growth. Our analysis indicates that initially flat, linear invading fronts exhibit Kardar-Parisi-Zhang (KPZ) roughening in one transverse dimension. Further, this finding implies, and is also confirmed by simulations, that the temporal correction to the asymptotic front velocity is of O(t(-2/3)).

Adaptation, Physiological↗

PubMed1997

B lymphocyte physiology: the beginning and the end.

Whereas lymphatic tissues were implicated as the chief sites for antibody production almost 100 years ago, three findings cemented the role of the plasma cell as the actual producer, namely the histological and tissue culture studies of Fagraeus, the beautiful immunofluorescent approach of Coons and his group, and the micromanipulation approach to the study of antibody formation by single cells introduced by Lederberg and myself. Proof that antibody-forming cells derived from B, rather than T, cells had to await the studies of Miller and Mitchell, with some minor technical contributions from myself. The physiology of the germinal centre also has a long history, and recently much interest has surrounded the relative roles of germinal centres as sites of somatic immunoglobulin V gene hypermutation and selection of high affinity B cells, versus the roles of extra-follicular proliferative foci as sources of the primary antibody response. Tolerance and self-antigens within the primary B lymphocyte repertoire is secured by clonal deletion within the bone marrow of those cells which are operationally the most threatening to the body, and a second level of functional impairment of B cell activity and life-span, capable of being induced centrally or peripherally, termed clonal anergy. As these concepts became progressively more refined through transgenic models of immunological tolerance, we turned our attention more towards tolerance within the secondary B lymphocyte repertoire. This is generated primarily inside germinal centres, where it appears that two quite separate mechanisms act as a bulwark against the possible creation of hypermutated anti-self cells. The first is that germinal centre activity and memory cell generation are dependent on antigen-specific, germinal centre-seeking CD4+ T cells, and if a putative anti-self mutant B cell gets no help because of T cell tolerance, it will not expand further. The second is a very specific mechanism confined to the germinal centre whereby antigen-specific B cells are especially sensitive to antigen-induced apoptosis if soluble, deaggregated antigen is presented to them before they reach the 'rescue' signal of follicular dendritic-cell-bound antigen. While some of the death in germinal centres is clearly apoptotic in nature, a further phenomenon observed electron microscopically relates to the formation of type B dark cells. It is not yet clear whether the DNA in this type of dying cell is cleaved. Transgenic expression of bcl-2 in germinal centre B lymphocytes confers incomplete protection from apoptosis caused by soluble antigen. The suggestion that at least some of this apoptosis is mediated via Fas-Fas ligand interactions is prompted by the observation that the apoptotic phenomenon is markedly reduced in lpr mice.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1992

Comparative anti-viral and anti-proliferative activity of PGA1 and PGJ2 against HTLV-I-infected MT-2 cells.

Prostaglandin (PG) A and J exert anti-viral and anti-proliferative effects in a number of experimental models. In particular, multiple treatments with PGAs prevent in vitro the clonal selection of HTLV-I-infected and potentially transformed cord-blood-derived mononuclear cells. Proliferation of HTLV-I-infected leukemic T cells is refractory in most cases to conventional anti-blastic therapy. We examined whether these cyclopentenone PGs might control cell proliferation and/or alter virus replication also in HTLV-I-transformed cells. We show that PGA1 and PGJ2 can exert powerful control of proliferation of the HTLV-I-immortalized, virus-producing MT-2 cell line, in a concentration-dependent fashion. Cells were preferentially arrested at the G1/S interface by treatment with PGA1 or PGJ2 without any detectable cellular toxicity. The anti-proliferative effect of PG treatment was independent of the growth phase of MT-2 cells, since both asynchronous and synchronous cells were sensitive to treatment. This effect was accompanied by an increase in the synthesis of a 70 kDa heat-shock protein (HSP70). However, synthesis of HSP70 was induced to a much greater extent by PGJ2 than by PGA1 at the same concentration. Neither PGA1 or PGJ2 inhibited the transcription of HTLV-I in MT-2 cells, but treatment with PGJ2, and not with PGA1, moderately inhibited the synthesis of viral proteins, i.e., p40 Tax and p19 core proteins. Moreover, infection of recipient K562 cells was significantly inhibited after pre-treatment of MT-2 cells with PGJ2 14 hr before or co-treatment at the onset of the co-culture with K562 cells. This effect was not obtained when MT-2 cells were repeatedly pre-treated with PGJ2 for 1 week before co-culturing. This suggests that reduced infection could be related to impairment of some step in virus-transmission phase.

Cell Division↗

PubMed1993

Effects of retinoic acid on cartilage differentiation in a chondrogenic cell line.

Previously we have isolated the monopotential chondrogenic cell line RCJ 3.1 C5.18 from the multipotential mesenchymal cell line RCJ 3.1 [Grigoriadis et al.: Endocrinology, 125:2103-2110, 1989]. When cultured for approximately 20 days under appropriate conditions, these cells from cartilage nodules. In the present investigation, we have used this cell line to study the effects of all-trans retinoic acid (RA) on chondroblast differentiation, cartilage formation, and cartilage degradation. Continuous exposure of cultures to RA (0.01-100 nM) inhibited chondroblast differentiation and glycosaminoglycan (GAG) accumulation in a dose-dependent manner, without comparable effects on cell growth. Pulse treatment with RA for various 4 day periods during a 17-24 day culture period established that RA inhibited differentiation of chondroprogenitors at all periods tested. These effects were reversible, except for part of the effect on early chondroprogenitors. Treatment with RA on days 13-17 in 17 day cultures not only resulted in cessation of cartilage formation, but also in disappearance of pre-existing cartilage nodules. We demonstrated that this was associated with RA-induced downregulation of GAG synthesis and increased degradation of cartilage proteoglycans. Hence, the inhibitory effects of RA on cartilage formation consist of inhibition of chondroblast differentiation, inhibition of GAG synthesis by differentiated chondroblasts, and stimulation of cartilage proteoglycan degradation by differentiated chondroblasts and/or chondrocytes. These results indicate that the clonal monopotential chondrogenic cell line RCJ 3.1 C5.18 forms a good model system to study the effects of retinoids on cartilage differentiation, formation, and degradation.

Animals↗

PubMed1986

Insulin secretory responses of a clonal cell line of simian virus 40-transformed B cells.

We have evaluated the potential of the clonal insulin-secretory cell line HIT-T15 as a model system for investigating stimulus-secretion coupling in pancreatic B cells. In contrast to other cell lines, HIT cell insulin secretion was consistently stimulated 2- to 3-fold by D-glucose. The maximally effective concentration of glucose was 10 mmol/l; between 2 and 10 mmol/l glucose the increase in insulin release was paralleled by an increased rate of glucose oxidation. The main characteristics of glucose-stimulated insulin release by HIT cells were essentially similar to those of normal islets. Thus, the response was specific for metabolizable sugars (D-mannose and D-glyceraldehyde stimulated insulin release but L-glucose and D-galactose were ineffective); markedly dependent on extracellular Ca2+ concentration; potentiated by forskolin, glucagon, acetylcholine and 12-O-tetradecanoyl phorbol 13-acetate; inhibited by adrenaline or somatostatin; showed a biphasic pattern of release in perifusion experiments, with both phases being potentiated by forskolin. The secretory response of the HIT cells to amino acids was also similar to that of normal islets. Thus, L-leucine and its deamination product 2-ketoisocaproate were effective stimuli, whereas L-isoleucine and L-glutamine were ineffective. Insulin release from HIT cells could also be evoked by the sulphonylureas glibenclamide and tolbutamide and by an increase in concentration of extracellular K+ to 40 mmol/l. The content of cyclic AMP in HIT cells was increased modestly by glucose but not by an increase in extracellular K+. Forskolin elicited a 4-fold increase in cyclic AMP content. We conclude that HIT cells retain the essential features of the insulin secretory response of normal B cells and represent an important tool for further biochemical characterization of the secretory system.

Animals↗

PubMed2002

The relationship of aplastic anemia and PNH.

Bone marrow failure has been regarded as one of the triad of clinical manifestations of paroxysmal noctumal hemoglobinuria (PNH), and PNH in turn has been described as a late clonal disease evolving in patients recovering from aplastic anemia. Better understanding of the pathophysiology of both diseases and improved tests for cell surface glycosylphosphatidylinositol (GPI)-linked proteins has radically altered this view. Flow cytometry of granulocytes shows evidence of an expanded PNH clone in a large proportion of marrow failure patients at the time of presentation: in our large NIH series, about 1/3 of over 200 aplastic anemia cases and almost 20% of more than 100 myelodysplasia cases. Clonal PNH expansion (rather than bone marrow failure) is strongly linked to the histocompatability antigen HLA.-DR2 in all clinical varieties of the disease, suggesting an immune component to its pathophysiology. An extrinsic mechanism of clonal expansion is also more consistent with knock-out mouse models and culture experiments with primary cells and cell lines, which have failed to demonstrate an intrinsic proliferative advantage for PNH cells. DNA chip analysis of multiple paired normal and PIG-A mutant cell lines and lymphoblastoid cells do not show any consistent differences in levels of gene expression. In aplastic anemia/PNH there is surprisingly limited utilization of the V-beta chain of the T cell receptor, and patients' dominant T cell clones, which are functionally inhibitory of autologous hematopoiesis, use identical CDR3 regions for antigen binding. Phenotypically normal cells from PNH patients proliferate more poorly in culture than do the same patient's PNH cells, and the normal cells are damaged as a result of apoptosis and overexpress Fas. Differences in protein degradation might play a dual role in pathophysiology, as GPI-linked proteins lacking an anchor would be predicted to be processed by the proteasome machinery and displayed in a class I H.A. context, in contrast to the normal pathway of cell surface membrane recycling, lysosomal degradation, and presentation by class II HLA. The strong relationship between a chronic, organ-specific immune destructive process and the expansion of a single mutant stem cell clone remains frustratingly enigmatic but likely to be the result of interesting biologic processes, with mechanisms that potentially can be extended to the role of inflammation in producing premalignant syndromes.

Anemia, Aplastic↗