Biomedical subjects

A Schedle

Publications and source records attributed to A Schedle.

At least 19 recordsLinked to original sources

PubMed2006

Root canal system in the mesiobuccal root of the maxillary first molar: an in vitro comparison study of computed tomography and histology.

OBJECTIVES: The purpose of this study was to investigate a new diagnostic approach to the examination of the canal configuration of the mesiobuccal root of the maxillary first molar. MATERIALS AND METHODS: High-resolution computed tomography (CT) was compared with histology in vitro. There were 152 teeth investigated and classified according to Weine and Vertucci. RESULTS: CT describes the exact canal configuration, verifying information identical to histology, and thus serving as the "gold standard" in vitro. With regard to canal position, 9 (5.92%) of the teeth examined were Vertucci type 1, 48 (31.58%) were Vertucci type 2, 91 (59.87%) were Vertucci type 4, 1 (0.66%) was Vertucci type 5, 1 (0.66%) was Vertucci type 6. Of the 152 teeth examined, 3 (1.97%) could not be classified using Weine, 2 (1.31%) could not be classified according to either Weine or Vertucci, and no Vertucci types 3, 7 or 8 were identified. CONCLUSIONS: CT offers complete information on the number and configuration of root canals. As the root canal configuration of the adult does not change rapidly, CT investigations can be used for multiple subsequent treatments.

Adult↗

PubMed2003

Longevity of direct resin composite restorations in posterior teeth.

This review is a survey of prospective studies on the clinical performance of posterior resin composites published between 1996 and 2002. Material, patient- and operator-specific data, observation periods, isolation methods of the operative field, and failure rates are detailed in tables. The data were evaluated statistically in order to assess the role of materials (filler size, bonding system, base materials [e.g. glass ionomer cements], and lining materials), study design, and personnel on failure rates. The primary reasons for composite failure were secondary caries, restoration fracture, and marginal defects. The influence of different commercial material brands on failure rates was not evaluated due to the great variety of test substances and the lack of material-specific documentation. Effects of the isolation method of the operative field (rubber dam or cotton rolls) and the professional status of operators (university or general dentist) on composite failure rates were not found to be significant. Observation periods varied from 1 to 17 years, and failure rates ranged between 0% and 45%. A linear correlation between failure rate and observation period was found (P<0.0001). Thirteen of 24 studies were terminated after 3 years, while seven studies continued for more than 10 years, indicating that favourable results for composite materials are frequently based on short-term results, despite higher dropout rates in longer studies. To determine accurately the risk for patients, long-term, randomised, controlled clinical trials of treatment outcomes with composites used in posterior teeth are clearly needed.

Bicuspid↗

PubMed2002

Ag, Cu, Hg and Ni ions alter the metabolism of human monocytes during extended low-dose exposures.

The monocyte and macrophage play an important role in the biological response to dental biomaterials. However, the effects of low-level, extended exposures of monocytes to metal ions which are known to be released from dental alloys is not known. Thus, in the current study we characterized the metabolic activity of monocytes in the presence of low doses of Ag, Cu, Hg and Ni ions for up to 4 weeks. THP-1 human monocytes were exposed in vitro to concentrations of metal ions at 1-10% of those known to be lethal during 24 h exposures. Mitochondrial function [succinic dehydrogenase (SDH) activity] and total cellular protein [bicinchoninic acid (BCA) assay] were assessed at weekly intervals during metal exposure. Each metal ion caused a unique pattern of effects from the monocytes. These effects were sometimes delayed until several weeks into the exposure (Cu, Ni). Large increases in total protein or SDH activity per cell were observed (Cu 150%, Hg 40-60%, Ni 50%), but these increases were always transient. The differences between concentrations with minimal effects and those which were lethal (8 versus 12 micromol L(-1) for Ag, 1.0 versus 1.5 micromol L(-1) for Hg) were small. Finally, concentrations which caused total suppression of cellular activity were sometimes preceded by an increased activity (Hg, Ni). We concluded that metal ions alter monocyte metabolic activity during extended exposures in vitro, but that the concentrations required are often near long-term lethal levels. Clinically, these results imply that the levels of metals released from dental alloys may be significant to monocytic function.

Cells, Cultured↗

PubMed2000

Influence of dental amalgam and heavy metal cations on in vitro interleukin-1beta production by human peripheral blood mononuclear cells.

The influence of dental amalgam and heavy metal cations on interleukin-1beta (IL-1beta) expression by peripheral blood mononuclear cells from healthy donors was studied. A marked decrease in the production of IL-1beta was caused by freshly prepared amalgam or amalgam-conditioned culture medium, but not by amalgam aged for 6 weeks. When metal cations were added as salts, Cu(2+), Hg(2+), and Ag(+) at high concentrations (33.3 and 333.3 microM) were highly inhibitory. Among other heavy metal cations, Au(3+), Pt(4+), Ni(2+), Pd(2+), but not Ga(3+) or Sn(2+), inhibited IL-1beta production in a concentration-dependent manner. Flow cytometry studies indicated that Hg(2+) and Ag(+) strongly reduced the percentage of CD14(+) cells containing IL-1beta intracellularly. As shown by Northern blot analysis, Hg(2+) inhibited the level of IL-1beta-specific mRNA by 28% at 3.3 microM and completely at 33.3 microM. Only slight inhibitory effects were induced by Cu(2+) at 33.3 microM. Interestingly, Ag(+) at a concentration of 3.3 microM increased twofold the amount of IL-1beta-specific mRNA. Our data show that IL-1beta production is altered at protein and mRNA levels by components released from fresh amalgam and by other heavy metal cations, suggesting a role of these cations in changes in the cell phenotype and IL-1-mediated cell functions.

Blotting, Northern↗

PubMed2000

Effect of silver, copper, mercury, and nickel ions on cellular proliferation during extended, low-dose exposures.

Previous studies have demonstrated and quantified the cytotoxicity of metal ions in vitro, but the data from these reports have been limited to short-term exposures of metal ions to cells (24-72 h). Yet, the longer-term, low-dose effects of metal ions are most relevant to the clinical use of dental and other biomedical alloys. Thus, the purpose of the current study was to assess longer-term effects of ions of silver, copper, mercury, and nickel - four metal ions known to be released from dental alloys - on monocytes. THP-1 human monocytes were exposed to the metal ions for up to 4 weeks. Concentrations of the metal ions were 1-10% of those known to cause cytotoxicity with 24-h exposures. Cellular proliferation and cellular viability were measured weekly. Ag(1+) and Hg(2+) did not alter the percentage of nonviable cells, but Cu(2+) and Ni(2+) increased the nonviable component as a function of metal concentration. These effects were cumulative over the 4 weeks only for Ni(2+). All metal ions caused a significant reduction in cellular proliferation, but the pattern of the effect was unique to each metal ion, and the effects were often not evident until 3 or 4 weeks of exposure. The results of the current study indicate that metal ions released from metallic biomaterials may have adverse biological effects at concentrations lower than previously reported.

Biocompatible Materials↗

PubMed1999

Characteristic features of trabecular bone in edentulous maxillae.

Following tooth loss, the maxillary alveolar ridge is affected by extensive resorption and its cancellous bone substance undergoes intense remodeling processes. This is particularly important for endosseous implant surgery as the primary stability and thus the prognosis of endosseous implants depends on the cancellous bone density and structure of the alveolar ridge. To analyze the structure of alveolar trabecular bone, 156 sections were obtained from 52 edentulous maxillae (29 female, 23 male; mean age: 72.5 years) from the lateral incisor, first premolar, and first molar regions. The structural histomorphometric analysis was performed on cancellous bone of the section surfaces using semiautomatic image analysis. The following parameters were measured: trabecular bone volume, trabecular number, trabecular thickness, trabecular plate separation and trabecular interconnection. All examined parameters showed an extreme range of variation. A difference of more than 45% between the highest (= 51.93%) and the lowest (= 6.73%) trabecular bone volumes was found. Furthermore, the measurements showed that trabecular bone volume, thickness and number were distinctly lower in the molar region than in the incisal and premolar regions. Significant sex-specific differences were found in all investigated regions, female maxillae showing a smaller amount and a lower connectivity of cancellous bone than male maxillae.

Adult↗

PubMed1998

Effects of dental amalgam and its components of histamine release from human basophils and tissue mast cells.

Recent studies have shown that metal ions can be released from dental amalgam or other dental materials, and can cause toxic effects on various cells. In this study, the effects of amalgam-conditioned culture medium (ACCM), components of amalgam (Ag+, Cu2+, Sn2+, Hg2+) and dental composite-conditioned culture medium (CCCM) on histamine release from human blood basophils (healthy subjects, n = 3) and tissue mast cells (n = 3) were analyzed. ACCM and CCCM were prepared using either fresh or 6-weeks-aged specimens. Of the metal ions tested, Ag+, and Hg2+ were found to induce histamine release from basophils (Ag+, 0.33 mM: 83 +/- 11% vs Hg2+, 0.33 mM: 100% vs control medium: 5 +/- 5%) and mast cells (Ag+, 0.33 mM: 91 +/- 16% vs Hg2+, 0.33 mM: 99 +/- 1% vs control: 2 +/- 1%), whereas no effects were seen with Cu2+ and Sn2+. Neither ACCM from freshly prepared amalgam nor ACCM from 6-weeks aged amalgam, produced histamine release in basophils or mast cells. Inductively coupled plasma atomic emission spectrometry (ICP) revealed that the Ag(+)- and Hg(2+)-concentrations in ACCM were below the range in which histamine release occurred. Similar to ACCM, no effects on basophils or mast cells were observed with CCCM. In summary, our data show that distinct metal ions present in dental amalgam, can induce (toxic) histamine liberation from basophils and mast cells. However, the amounts of metal ions released from amalgam apparently were too low, to cause histamine release.

Basophils↗

PubMed1998

Metal ion-induced toxic histamine release from human basophils and mast cells.

Recent data suggest that distinct metal ions can be released from dental alloys or other biomaterials, and may cause toxic effects on various cells. In this study, the effects of 14 metal ions on histamine release from human blood basophils (n = 4), isolated tissue mast cells (lung n = 8, uterus n = 2, skin n = 1, gingiva n = 1), the basophil cell line KU-812, and the mast cell line HMC-1 were analyzed. Of the 14 metal ions, Ag+ (0.33 mM) and Hg2+ (0.33 mM) were found to induce release of histamine in blood basophils, KU-812, mast cells, and HMC-1. The effects of Ag+ and Hg2+ were dose dependent and were observed within 60 min of incubation. In primary mast cells and basophils, AU3+ (0.33 mM) also induced histamine release, whereas no effects of Au3+ on HMC-1 or KU-812 cells were seen. The other metal ions showed no effects on primary or immortal cells within 60 min. However, Pt4+ (0.33 mM) induced histamine liberation in HMC-1 and lung mast cells after 12 h. The Ag+- and Hg2+-induced rapid release of histamine from HMC-1 was associated with ultrastructural signs of necrosis, but not apoptosis. In contrast, prolonged exposure to Pt4+ (0.33 mM, 14 h) induced apoptotic cell death in HMC-1 cells, as assessed by electron microscopy and DNA analysis. Together, certain metal ions induce distinct cytopathogenic effects in mast cells and basophils. Whereas Ag+, Hg2+, and Au3+ cause direct toxicity, Pt4 causes cell death through induction of apoptosis. Whether such effects contribute to local adverse reactions to metal-containing biomaterials in vivo remains to be determined.

Basophils↗

PubMed1998

Effects of dental amalgam and heavy metal cations on cytokine production by peripheral blood mononuclear cells in vitro.

The effects of dental amalgam on cytokine production by human peripheral blood mononuclear cells (PBMC) from healthy donors were analyzed. To induce cytokine production, PBMC were stimulated with lipopolysaccharide, phytohemagglutinin, or staphylococcal enterotoxin A and cultured for 48 h in the presence of either freshly prepared amalgam, aged amalgam, or amalgam-conditioned culture medium (ACCM). The concentrations of several cytokines were measured in PBMC supernatants by enzyme-amplified sensitivity immunoassays (EASIAs). Freshly prepared amalgam as well as ACCM induced a decrease in the production of interferon-gamma (IFN-gamma) and interleukin-10 (IL-10), and an increase in the concentrations of tumor necrosis factor-alpha (TNF-alpha). Both fresh amalgam and ACCM showed no effects on IL-2, IL-6, or granulocyte-macrophage colony-stimulating factor levels. Amalgam aged for 6 weeks did not affect the concentration of any of the above cytokines. To investigate which heavy metal cations released from amalgam caused the observed immunomodulatory effects, Cu2+, Hg2+, and Sn2+, which were detected in amalgam supernatants by inductively coupled plasma atomic spectrophotometry, were added as salts to the cultures. Cu2+ and Hg2+ induced a decrease in IFN-gamma and IL-10 levels, and Hg2+ an increase in TNF-alpha concentrations. Cytokine production was not significantly modulated by Sn2+. Under these experimental conditions, release of Ag+ into culture medium was not detectable. However, Ag+ markedly suppressed the production of IFN-gamma, IL-10, and TNF-alpha. In summary, our results show that fresh amalgam, but not amalgam aged for 6 weeks, causes changes in the cytokine pattern of PBMC in vitro, and that these effects are due to the release of Cu2+ and Hg2+.

Cations↗

PubMed1998

Cytotoxic effects of dental composites, adhesive substances, compomers and cements.

OBJECTIVES: Although research interest in biocompatibility of dental materials has been increasing, findings are frequently controversial and non-harmonized experimental approaches often lead to the production of contradictory results. The aim of this study was to compare the cytotoxic effects of six different light-cured dental composites, one compomer, one advanced glass-ionomer, two glass-ionomer cements, two zinc phosphate cements, one calcium hydroxide liner, one composite cement and one carboxylate cement with the same standardized cell-culture system. Two composites, one compomer and one advanced glass-ionomer were also tested in combination with the appropriate bonding substances and surface primers. METHODS: Specimens were added to the cultures immediately after production or after preincubation for 1, 2 or 7 days or 6 weeks under cell-culture conditions. Specimens were incubated with L-929 fibroblasts for 72 h and cell numbers determined by flow cytometry. RESULTS: All freshly prepared composite materials were cytotoxic. These effects diminished with increased preincubation times and were not significant after 7 days. Combinations of composites and bonding substances were still cytotoxic after preincubation for 7 days, but not after 6 weeks. Combinations of compomers and bonding substances demonstrated stronger toxicity than composites, although these effects were reduced earlier during preincubation. Glass-ionomer and phosphate cements showed similar effects to the composites with the exception of carboxylate cement, which demonstrated severe and persistent effects even after 6 weeks' preincubation. Together, our data provide evidence that all dental materials tested are cytotoxic immediately after production and that these effects are reduced after different preincubation periods in most cases. SIGNIFICANCE: Tested with a standardized cell-culture system, differences in toxicological potency between various commonly used dental materials were observed. Cytotoxicity data from standardized protocols should form the basis of screening the cytotoxic effects of new materials.

Adhesives↗

PubMed1998

Phenotypic and functional characterization of mast cells derived from renal tumor tissues.

Mast cells (MCs) originate from multipotent hematopoietic progenitor cells. However, MCs in various organs are heterogenous in terms of mediator or receptor expression and response to diverse stimuli. We characterized the phenotype and functional properties of human renal mast cells (HRMCs). Tissue was obtained from 17 patients suffering from renal tumors (transitional cell carcinoma, n = 4; renal cell carcinoma, n = 13). HRMCs were isolated by collagenase digestion. Double staining with toluidine blue and immunofluorescence using monoclonal antibodies (mAbs) revealed expression of stem cell factor (SCF)-receptor (c-kit/CD117), CD9, CD29, CD33, CD43, CD44, CD54, and CD63 on HRMCs. In contrast, HRMCs were not recognized by mAbs to CD2, CD3, CD4, CD11b, CD14, CD15, CD16, CDw17, CD19, or CD23. HRMCs were also negative for CD116 (granulocyte-macrophage colony-stimulating factor [GM-CSF] receptor alpha), CD123 (interleukin [IL]-3Ralpha), CD121a (IL-1R type I), CD122 (IL-2Rbeta), and CD127 (IL-7R) and were also found to lack C5aR (CD88). Ligand-induced activation of HRMCs through immunoglobulin (Ig)E-R or SCF-R (c-kit) resulted in histamine secretion (control: <10%; alphaIgE, 1 microg/mL: 50.12 +/-5.18%; rhSCF, 100 ng/mL: 29.24 +/- 22.39), whereas recombinant C5a, erythropoietin (EPO), IL-1 through 10, and GM-CSF exerted no effects. As determined by in situ staining, HRMCs contained tryptase, but only low or undetectable amounts of chymase. Electron microscopy confirmed the presence of MCs in renal tissues and revealed a scroll-rich granule population in HRMCs. Together, HRMCs are tryptase+, C5aR- mast cells exhibiting phenotypic and functional properties similar to those of lung MCs.

Adult↗

PubMed1995

Response of L-929 fibroblasts, human gingival fibroblasts, and human tissue mast cells to various metal cations.

Recent data suggest that under certain conditions, various metal cations are released from dental alloys. These ions may produce adverse effects in various cell types in vivo. In this study, the cytopathogenic effects of 13 metal cations on murine L-929 fibroblasts, human gingival fibroblasts, and human tissue mast cells were analyzed in vitro. Several metal cations (dose range, from 0.0033 to 1.0 mmol/L) were found to induce dose-dependent inhibition of 3H-thymidine incorporation into cultured fibroblasts. The rank order of potency (lowest observed effect level, LOEL) for L-929 fibroblasts was: Ag+ > Pt4+ > Co2+ > In3+ > Ga3+ > Au3+ > Cu2+ > Ni2+ > Zn2+ > Pd2+ > Mo5+ > Sn2+ > Cr2+. A similar rank order of potency was obtained for primary human gingival fibroblasts: Pt4+ > Ag+ > Au3+ > In3+ > Ga3+ > Ni2+ > Co2+ > Zn2+ > Cu2+ > Cr2+ > Pd2+ > Mo5+ > Sn2+. In primary human mast cells, Ag+ and Au3+ caused dose-dependent toxic histamine release, whereas the other metal cations were ineffective over the dose range tested. To investigate the mechanism of metal cation-induced effects, we performed DNA as well as electron microscopic analyses on cultured fibroblasts. Both the DNA pattern and the ultrastructure of L-929 cells and gingival fibroblasts after exposure to cytopathogenic metal cations revealed signs of necrosis but no signs of apoptosis. Together, our data provide evidence that various metal cations produce dose-dependent cytopathogenic effects in distinct cell types, including human gingival fibroblasts and human tissue mast cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Tumour necrosis factor-alpha augments the expression of Fc IgE receptor (Fc epsilon RII/CD23) on human monocytic cell lines and down-regulates interleukin-4-driven Fc epsilon RII expression on monocytes.

We investigated the expression of the low affinity Fc IgE receptor (Fc epsilon RII/CD23) on the human monocytic cell lines U937, THP-1, Mono-Mac-6, and cultured human peripheral blood monocytes under stimulation with human tumour necrosis factor-alpha (TNF-alpha) and other cytokines. Fc epsilon RII was demonstrated by flow cytometry analysis employing the anti-Fc epsilon RII monoclonal antibody 3-5. TNF-alpha alone had a weak but significant stimulating effect on the Fc epsilon RII expression on the cell lines U937 and THP-1, and very modestly on Mono-Mac-6 cells. TNF-alpha strongly synergized with interferon-gamma (IFN-gamma) and interleukin-4 (IL-4). IFN-alpha per se was ineffectual, but was able to increase the TNF-alpha effect. Furthermore, the action of TNF-alpha was slightly augmented by human IL-6. Similar effects were noted with TNF-beta alone or in combination with other cytokines. Interestingly, on human monocytes TNF-alpha weakly reduced the basal level of Fc epsilon RII, and markedly diminished the IL-4-induced Fc epsilon RII expression. Our results indicate that several cytokines may interact in a cytokine network to modulate Fc epsilon RII expression on monocytic cell lines. On human blood monocytes, TNF-alpha, like IFN-gamma or IL-6, counteracts the IL-4-induced Fc epsilon RII expression. These data suggest different regulatory pathways of Fc epsilon RII expression on blood monocytes and myelomonocytic cell lines.

Cell Line↗

PubMed1992

[Psychosocial development in cystic fibrosis].

This brief review outlines of the current research on psychosocial stress and coping of children and adolescents with cystic fibrosis (CF) and of their families. Next to medical facts aspects of normal development as well as specific problems in individual periods of life are presented proceeding from an individual to a familial view. Requirements for a comprehensive bio-psychosocial care are raised. Flexible models of care have to take into account the circular process of individual and familial coping with chronic disease. Helpful support of CF-Patients and their families requires interdisciplinary cooperation in the CF-team.

Adaptation, Psychological↗

PubMed1992

Nucleolar morphology and rDNA in situ hybridisation in monocytes.

The aim of this study was to correlate morphological changes of nucleoli of non-proliferating monocytes to their functional activity, since nucleolar morphology is currently considered as a diagnostic marker for cell proliferation. Monocytes from healthy donors were fractionated by current counterflow centrifugation and kept in culture for 6 days. Cells were stimulated by the addition of 200 units/ml interferon gamma (IFN gamma). Under this stimulus the monocytes show no proliferation but a strongly augmented expression of type I Fc IgG receptor, human leucocyte antigen DR, human leucocyte antigen DP and human leucocyte antigen DQ. Morphological changes after stimulation included the appearance of multinucleated cells, typical signs of the activation of rRNA synthesis indicated by an increase in nucleolar size, and changes in nucleolar structure such as the appearance of reticulate and compact nucleoli. The number of nucleolus organiser regions (NORs) visualised by in situ hybridisation was compared with the position and number of nucleoli visualised by silver staining in interphase cells. In comparison with control cultures, activated monocytes show a distinct increase in the number of those NORs that take part in the formation of nucleoli. Our results show that, in non-proliferating activated monocytes, the morphology of nucleoli and the increase of NOR activity are similar to those in proliferating cells. NOR activation is therefore an indicator for cellular activity, but is not necessarily correlated with proliferation.

Cell Division↗

PubMed1991

IL-6 augments Fc IgE receptor (Fc epsilon RII/CD23) expression on human monoblastic/monocytic cell lines U937, THP-1, and Mono-Mac-6 but not on blood monocytes. Regulatory effects of IL-4 and IFN-gamma.

Human monoblastic/monocytic leukemia cell lines U937, THP-1, Mono-Mac-6, and blood monocytes were incubated with various concentrations of human rIL-6 and other cytokines and analyzed for their capacity to bind several anti-Fc epsilon RII/CD23 mAb. A marked and dose-dependent increase in the percentage of CD23+ cells, as well as in the mean channel fluorescence intensity, as demonstrated by FACS analysis, was noted after 8- to 72-h incubation of U937 cells with 1 to 1000 U/ml of human rIL-6. Furthermore, rIL-4 synergized with rIL-6 and rIFN-tau in augmenting the Fc epsilon RII expression on U937 cells, whereas rIFN-tau and rIL-6 showed rather additive effects. The enhancement of CD23 expression on IL-6-treated U937 cells was blocked by anti-IL-6 antibodies. Northern blot analysis, employing cDNA probes for Fc epsilon RII, showed that U937 cells contain Fc epsilon RII-specific mRNA. The level of Fc epsilon RII-encoding mRNA was evidently increased by treatment of U937 cells with human rIL-6, rIL-4, or with rIL-6 + rIL-4. The expression of CD23 on THP-1 and Mono-Mac-6 cells was increased slightly by rIL-6 and markedly by rIL-4, rIFN-tau, or a mixture of them. Approximately 14% of blood monocytes, isolated from apparently healthy donors, constitutively possess Fc epsilon RII. In contrast to the cell lines, the Fc epsilon RII density and the percentage of blood monocytes bearing Fc epsilon RII was not augmented by IL-6. Furthermore, rIL-6, and more evidently rIFN-tau, down-regulate rIL-4-driven Fc epsilon RII expression on monocytes but not on monocytic cell lines. Our findings point to differences in the capability of mononuclear phagocytes to respond to cytokine treatment, which may be differentiation dependent, and suggest separate regulatory pathways.

Antigens, CD↗

PubMed1991

Transcribed and nontranscribed parts of the human ribosomal gene repeat show a similar pattern of distribution in nucleoli.

The distribution pattern of the transcribed and nontranscribed parts of human ribosomal RNA genes were visualized simultaneously in the same cells by nonautoradiographic in situ hybridization. DNA probes labeled with either digoxigenin or biotin were detected in the same cells by different fluorescence systems. The signals from both the transcribed and nontranscribed parts showed a similar distribution pattern. This finding is not compatible with the conclusion, suggested by earlier studies, that the transcribed and nontranscribed parts of the rRNA genes are located at different sites within the nucleoli or in different nucleolar components.

Cell Nucleolus↗

PubMed1990

Nucleolus organizer regions in human lymphocytes as studied with premature chromosome condensation.

Non-stimulated human lymphocytes from peripheral blood usually contain only one ring-shaped nucleolus. Polyethyleneglycol-mediated cell fusion with mitotic Chinese hamster ovary cells induces premature chromosome condensation in human lymphocytes. Subsequent silver staining reveals that more than one nucleolus organizer region (NOR) is silver-positive and frequently participates in the formation of "satellite associations". It can therefore be concluded that more than one NOR contributes to the ring-shaped nucleoli of lymphocytes in human peripheral blood and that they may be transcriptionally active. During phytohemagglutinin (PHA) stimulation, the number of silver-positive NORs, the number of nucleoli and the number of chromosomes participating in "satellite associations" increase.

Chromosomes, Human↗