Interaction of human osteoblast-like Saos-2 and MG-63 cells with thermally oxidized surfaces of a titanium-niobium alloy

An investigation was made of the adhesion, growth and differentiation of osteoblast-like MG-63 and Saos-2 cells on titanium (Ti) and niobium (Nb) supports and on TiNb alloy with surfaces oxidized at 165°C under hydrothermal conditions and at 600°C in a stream of air. The oxidation mode and the chemical composition of the samples tuned the morphology, topography and distribution of the charge on their surfaces, which enabled us to evaluate the importance of these material characteristics in the interaction of the cells with the sample surface. Numbers of adhered MG-63 and Saos-2 cells correlated with the number of positively-charged (related with the Nb₂O₅ phase) and negatively-charged sites (related with the TiO₂ phase) on the alloy surface. Proliferation of these cells is correlated with the presence of positively-charged (i.e. basic) sites of the Nb₂O₅ alloy phase, while cell differentiation is correlated with negatively-charged (acidic) sites of the TiO₂ alloy phase. The number of charged sites and adhered cells was substantially higher on the alloy sample oxidized at 600°C than on the hydrothermally treated sample at 165°C. The expression values of osteoblast differentiation markers (collagen type I and osteocalcin) were higher for cells grown on the Ti samples than for those grown on the TiNb samples. This was more particularly apparent in the samples treated at 165°C. No considerable immune activation of murine macrophage-like RAW 264.7 cells on the tested samples was found. The secretion of TNF-α by these cells into the cell culture media was much lower than for either cells grown in the presence of bacterial lipopolysaccharide, or untreated control samples. Thus, oxidized Ti and TiNb are both promising materials for bone implantation; TiNb for applications where bone cell proliferation is desirable, and Ti for induction of osteogenic cell differentiation.

Adhesion and Growth of Vascular Smooth Muscle Cells on Nanostructured and Biofunctionalized Polyethylene

Cell colonization of synthetic polymers can be regulated by physical and chemical modifications of the polymer surface. High-density and low-density polyethylene (HDPE and LDPE) were therefore activated with Ar⁺ plasma and grafted with fibronectin (Fn) or bovine serum albumin (BSA). The water drop contact angle usually decreased on the plasma-treated samples, due to the formation of oxidized groups, and this decrease was inversely related to the plasma exposure time (50–300 s). The presence of nitrogen and sulfur on the polymer surface, revealed by X-ray photoelectron spectroscopy (XPS), and also by immunofluorescence staining, showed that Fn and BSA were bound to this surface, particularly to HDPE. Plasma modification and grafting with Fn and BSA increased the nanoscale surface roughness of the polymer. This was mainly manifested on HDPE. Plasma treatment and grafting with Fn or BSA improved the adhesion and growth of vascular smooth muscle cells in a serum-supplemented medium. The final cell population densities on day 6 after seeding were on an average higher on LDPE than on HDPE. In a serum-free medium, BSA grafted to the polymer surface hampered cell adhesion. Thus, the cell behavior on polyethylene can be modulated by its type, intensity of plasma modification, grafting with biomolecules, and composition of the culture medium.

Effect of different surface nanoroughness of titanium dioxide films on the growth of human osteoblast-like MG63 cells

Cell behavior depends strongly on the physical and chemical properties of the material surface, for example, its chemistry and topography. The authors have therefore assessed the influence of materials of different chemical composition (i.e., glass substrates with and without TiO(2) films in anatase form) and different surface roughness (R(a) = 0, 40, 100, or 170 nm) on the adhesion, proliferation, and osteogenic differentiation of human osteoblast-like MG63 cells. On day 1 after seeding, the largest cell spreading area was found on flat TiO(2) films (R(a) = 0 nm). On TiO(2) films with R(a) = 170 nm, the cell spreading area was larger and the number of initially adhering cells was higher than the values on the corresponding uncoated glass. On day 3 after seeding, the cell number was higher on the TiO(2) films (R(a) = 0 and 40 nm) than on the corresponding glass substrates and the standard polystyrene dishes. On day 7, all TiO(2) films contained higher cell numbers than the corresponding glass substrates, and the cells on the TiO(2) films with R(a) = 40 and 100 nm also contained a higher concentration of β-actin. These results indicate that TiO(2) coating had a positive influence on the adhesion and subsequent proliferation of MG63 cells. In addition, on all investigated materials, the cell population density achieved on day 7 decreased with increasing surface roughness. The concentration of osteocalcin, measured per mg of protein, was significantly lower in the cells on rougher TiO(2) films (R(a) = 100 and 170 nm) than in the cells on the polystyrene dishes. Thus, it can be concluded that the adhesion, growth, and phenotypic maturation of MG63 cells were controlled by the interplay between the material chemistry and surface topography, and were usually better on smoother and TiO(2)-coated surfaces than on rougher and uncoated glass substrates.

Enhanced growth and osteogenic differentiation of human osteoblast-like cells on boron-doped nanocrystalline diamond thin films

Intrinsic nanocrystalline diamond (NCD) films have been proven to be promising substrates for the adhesion, growth and osteogenic differentiation of bone-derived cells. To understand the role of various degrees of doping (semiconducting to metallic-like), the NCD films were deposited on silicon substrates by a microwave plasma-enhanced CVD process and their boron doping was achieved by adding trimethylboron to the CH₄:H₂ gas mixture, the B∶C ratio was 133, 1000 and 6700 ppm. The room temperature electrical resistivity of the films decreased from >10 MΩ (undoped films) to 55 kΩ, 0.6 kΩ, and 0.3 kΩ (doped films with 133, 1000 and 6700 ppm of B, respectively). The increase in the number of human osteoblast-like MG 63 cells in 7-day-old cultures on NCD films was most apparent on the NCD films doped with 133 and 1000 ppm of B (153,000±14,000 and 152,000±10,000 cells/cm², respectively, compared to 113,000±10,000 cells/cm² on undoped NCD films). As measured by ELISA per mg of total protein, the cells on NCD with 133 and 1000 ppm of B also contained the highest concentrations of collagen I and alkaline phosphatase, respectively. On the NCD films with 6700 ppm of B, the cells contained the highest concentration of focal adhesion protein vinculin, and the highest amount of collagen I was adsorbed. The concentration of osteocalcin also increased with increasing level of B doping. The cell viability on all tested NCD films was almost 100%. Measurements of the concentration of ICAM-1, i.e. an immunoglobuline adhesion molecule binding inflammatory cells, suggested that the cells on the NCD films did not undergo significant immune activation. Thus, the potential of NCD films for bone tissue regeneration can be further enhanced and tailored by B doping and that B doping up to metallic-like levels is not detrimental for cells.

Nanodiamond as promising material for bone tissue engineering

The adhesion, growth and differentiation of human osteoblast-like MG 63 cells were investigated in cultures grown on nanostructured nanocrystalline diamond (NCD) films with either low surface roughness (rms of 8.2 nm) or hierarchically organized surfaces made of low roughness NCD films deposited on Si surfaces with the original microroughness (rms of 301.0 nm and 7.6 nm, respectively). The NCD films were grown using a microwave plasma-enhanced CVD method in an ellipsoidal cavity reactor. The films were treated in oxygen plasma to enhance the hydrophilic character of the diamond surface (water drop contact angle approx. 20 degrees). The samples were then sterilized by 70% ethanol, inserted into 12-well polystyrene multidishes (diameter 2.2 cm), seeded with human osteoblast-like MG 63 cells (40,000 cells/dish, 10,530 cells/cm2) and incubated in 2 ml of DMEM medium with 10% of fetal bovine serum. On day 3 after seeding, the cell numbers were significantly higher on the nanostructured NCD films (72,020 +/- 6540 cells/cm2) and also on the hierarchically micro- and nanostructured films (60200 +/- 6420 cells/cm2) than on the control polystyrene culture dish (40750 +/- 2,530 cells/cm2). The cells on hierarchically micro- and nanostructured diamond substrates also adhered over a significantly larger area (3730 +/- 180 microm2 compared to 2740 +/- 130 microm2 on polystyrene). The cell viability, measured by a LIVE/DEAD viability/cytotoxicity kit, reached 98% to 100% on both types of NCD films. The XTT test showed that the cells on both nanodiamond layers had significantly higher metabolic activity than those on the control polystyrene dish (approx. 2 to 3 times). Immunofluorescence staining of the cells on both NCD films revealed talin-containing focal adhesion plaques and beta-actin filaments, well apparent particularly at the cell periphery, as well as the presence of considerable amounts of osteocalcin, i.e., a marker of osteogenic cell differentiation. These results suggest that nanocrystalline diamond films give good support for adhesion, growth and differentiation of osteogenic cells and could be used for surface modification of bone implants in order to improve their integration with the surrounding bone tissue.

Acute and chronic effects of antidepressants on the G-protein alpha subunit profiles in vitro and in vivo

OBJECTIVES

Neurochemical studies on the etiopathogenesis of depression are also focusing on the transduction system beyond receptors. Trimeric G-proteins play a crucial role in the transmembrane signalling, signal amplification and intracellular processing. Abnormalities of G-protein levels are observed in subjects with depression, G-protein modulation is considered to play a role in the antidepressant mode of action.

METHODS

We studied acute or chronic administration of antidepressants from different pharmacological groups. We used immunochemical estimation (ELISA) of the main types of G-protein alpha subunits from isolated membranes of C6 glioma cells and rat brain tissue.

RESULTS

Significant elevation of G alpha q/11 subunits after chronic administration of sertraline and significant reduction of G alpha s subunit levels following both acute and chronic administrations of sertraline were found. In contrast, no significant effects on G alpha subunit levels following acute desipramine and moclobemide administration were observed in vitro. Chronic moclobemide effect in vivo is causing significant elevation of Galpha s and Galpha i1,2 subunit levels.

CONCLUSIONS

Results show involvement of antidepressant drugs in the C6 glioma signal transduction cascades modulation in dependence on the antidepressant class. Significant influence in the cAMP system modulation is observed after administration both SSRI and MAOA inhibitors. Astrocytoma cells - C6 glioma cells also can offer a model system of the glia where modulation of cell signalization cascades can influence cell functioning and production of neurotrophic factor molecules relevant to the antidepressant treatment and depression etiopathogenesis.

Constitutive expression of IL-18 and IL-18R in differentiated IEC-6 cells: effect of TNF-alpha and IFN-gamma treatment

The multifunctional cytokine interleukin-18 (IL-18) is an important mediator in intestinal inflammatory processes. The aim of this study was to evaluate the constitutive expression of IL-18 and its receptors (IL-18Ralpha and IL-18Rbeta) in intestinal epithelial cells (IEC) stimulated by tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). In addition, cellular proliferation and evaluation of brush border enzymes as differentiation markers were studied. Nontransformed rat intestinal epithelial IEC-6 cells were grown on an extracellular matrix (ECM) in medium with or without TNF-alpha, IFN-gamma, or a combination of both. Gene expression of IL-18, its receptors and apoptotic markers was evaluated using real-time PCR. Expression of IL-18Ralpha protein was demonstrated by flow cytometry and Western blot. Enzymatic activities of brush border enzymes and caspase-1 were determined. The constitutive expression of IL-18, IL-18Ralpha and IL-18Rbeta mRNAs and proteins were detected in IEC-6 cells. The biologically active form of IL-18 was released in response to TNF-alpha and IFN-gamma treatment. Exogenous IL-18 had no effect on cellular proliferation, brush border enzyme activities, and gene expression of apoptotic markers. However, the addition of IL-18 stimulated production and release of the chemokine IL-8. These data suggest that IEC-6 cells may be not only a source of IL-18 but also a target for its action.

Expression and enzymatic activity of dipeptidyl peptidase-IV in human astrocytic tumours are associated with tumour grade

Alterations in dipeptidyl peptidase-IV (DPP-IV) enzymatic activity are characteristic of malignant transformation. Through its well-characterized functionality in regulating the activity of bioactive peptides by removal of the N-terminal dipeptide, DPP-IV activity may have profound effects upon metastatic potential and cell growth. Although DPP-IV/CD26 (EC 3.4.14.5) is the canonical representative of the group, a number of other proteins including DPP-7, 8, 9, and seprase/fibroblast activation protein-alpha (FAP-alpha) have been shown to have similar enzymatic activity. This study was set up to address the relative representation and enzymatic activity of plasma membrane localized DPP-IV/CD26 and FAP-alpha in human brain and astrocytic tumours. In parallel, expression of CXCR4, receptor for glioma cell growth stimulator chemokine SDF-1alpha known to be a DPP-IV substrate, was investigated. This is the first report showing that non-malignant brain tissue contains a DPP-IV-like enzymatic activity attributable mostly to DPP-8/9, while the substantial part of the activity in glioma is due to increased DPP-IV/CD26, localized in both the vascular and parenchymal compartments. DPP-IV enzymatic activity increased dramatically with tumour grade severity. A grade-related increase in CXCR4 receptor paralleled the rise in DPP-IV expression and activity. These data might support a role for DPP-IV regulation of the CXCR4-SDF-1alpha axis in glioma development.

Adhesion and growth of vascular smooth muscle cells in cultures on bioactive RGD peptide-carrying polylactides

The surface of poly(L-lactide) (PLLA) films deposited on glass coverslips was modified with poly(DL-lactide) (PDLLA), or 1:4 mixtures of PDLLA and PDLLA-b-PEO block copolymers, in which either none, 5% or 20% of the copolymer molecules carried a synthetic extracellular matrix-derived ligand for integrin adhesion receptors, the GRGDSG oligopeptide, attached to the end of the PEO chain. The materials, perspective for vascular tissue engineering, were seeded with rat aortic smooth muscle cells (11,000 cells/cm(2)) and the adhesion, spreading, DNA synthesis and proliferation of these cells was followed on inert and bioactive surfaces. In 24-h-old cultures in serum-supplemented media, the number of cells adhering to the PDLLA-b-PEO copolymer was almost eight times lower than that on the control PDLLA surface. On the surfaces containing 5% and 20% GRGDSG-PEO-b-PDLLA copolymer, the number of cells increased 6- and 3-fold respectively, compared to the PDLLA-b-PEO copolymer alone. On PDLLA-b-PEO copolymer alone, the cells were typically round and non-spread, whereas on GRGDSG-modified surfaces the cell spreading areas approached those found on PDLLA, reaching values of 991 microm(2) and 611 microm(2) for 5% and 20% GRGDSG respectively, compared to 958 microm(2) for PDLLA. The cells on GRGDSG-grafted copolymers were able to form vinculin-containing focal adhesion plaques, to synthesize DNA and even proliferate in a serum-free medium, which indicates specific binding to the GRGDSG sequences through their adhesion receptors.

Occurrence of Lily mottle virus in Escarole

Lily mottle virus (LMoV), genus Potyvirus, an important virus of lily that also causes flower-breaking in tulip (1), is considered to have a natural host range restricted to the family Liliaceae. In 1996, escarole (Cichorium endivia L. var. latifolium LAM) plants growing in fields close to Torino, Italy, and showing mosaic and necrotic spots on outer leaves were infected by a potyvirus related to LMoV. The virus was identified by immunoelectron microscopy (IEM) done on experimentally infected Nicotiana benthamiana and Chenopodium quinoa. The virus isolated from escarole (LMoV-E) had an experimental host range similar to that of lily isolates of LMoV, although species within the Liliaceae were not tested. LMoV-E systemically infected all nine escarole cultivars and six of seven endive cultivars (C. endivia L. var. crispum LAM) but did not infect any of six lettuce and two chicory cultivars (C. intybus L. var. foliosum HEGI). Symptoms ranged from mild to severe mosaic and were generally more severe on escarole than on endive. Some of the same escarole, endive, and lettuce cultivars were inoculated with a typical LMoV isolate from lily (Le97/49, from A. F. L. M. Derks, the Netherlands), which induced mild systemic infections in only one escarole and one endive cultivar. Both cultivars were also susceptible to LMoV-E. LMoV-E was purified from N. benthamiana, and an antiserum was prepared. IEM decoration titer experiments were done with LMoV-E and four other LMoV isolates from Liliaceae and their homologous antisera. Heterologous titers ranging from identity to serological differentiation index values of 2 to 4 were obtained, confirming the identity of the escarole isolate as a LMoV strain and indicating considerable serological variability among LMoV isolates. In a field survey of endive and escarole crops in 1998, in the area where LMoV-E was first identified, the virus was again detected by enzyme-linked immunosorbent assay in 4 of 80 escarole plants tested. LMoV-E appears to be a LMoV strain particularly adapted to escarole. To our knowledge, this is the first report of LMoV identified in a naturally infected host outside monocotyledonous plants. Reference: (1) E. L. Dekker et al. J. Gen. Virol. 74:881, 1993.

First Report of Anemone Plants Infected by Ranunculus white mottle virus

Ranunculus white mottle virus (RWMV) (1), genus Ophiovirus, has been reported in crops of several cultivars of commercial ranunculus (Ranunculus asiaticus hybrids) during the 1990s in Liguria in Northwest Italy. Symptoms associated with RWMV in ranunculus are not clear-cut owing to the presence of mixed viral infections. During autumn 1999, a severe disease in commercial crops of anemone (Anemone coronaria) was noted in the same area. Plants appeared stunted with young leaves showing curling, deformation, and necrotic spotting. Disease incidence in some fields reached 40 to 50%. DAS- and TAS-enzyme-linked immunosorbent assays (ELISAs) for presence of RWMV and for the viruses most frequently infecting anemone in Italy were run on 24 field samples. Seven proved to be infected by RWMV in mixed infection with Cucumber mosaic virus subgroup II or with Tobacco necrosis virus. Ophiovirus-like particles were detected by negative staining and electron microscopy from sap extracts of field plants that were RWMV-positive by ELISA. Sap from these plants was also mechanically inoculated to indicator plants. Total RNAs were extracted from RWMV-infected field samples and from inoculated Nicotiana benthamiana and N. clevelandii and used in molecular tests. A DIG-DNA probe targeting the 1.8-kb RNA2 of RWMV was used in Northern blots and dot blots of total RNAs, confirming the infection in field samples and multiplication of the virus in test plants, unfortunately still in mixed infection. At present, it is difficult to evaluate RWMV symptomatology in anemone, but the presence of this virus in mixed infection seems to produce serious effects. This is the first report of RWMV in anemone. Reference: (1) A. M. Vaira et al. Arch. Virol. 142:2131, 1997.

Modulation of porphyrin derivatives accumulation in C6 glioma cells by drugs acting on beta-adrenergic receptors. A spectrofluorometric study

The pharmacological modulation of the uptake of porphyrin derivatives in cultured C6 glioma cells was investigated by means of spectrofluorometric analysis both in single cells and in cell homogenates. The influence of drugs acting as beta-receptor agonists or antagonists was studied in cells grown to semiconfluency. Isoproterenol (ISO), a beta-receptor agonist, enhanced the intracellular fluorescence intensity of both Photofrin and protoporphyrin IX (PpIX). A treatment with a beta-receptor antagonist I-propranolol (PRO), simultaneous with ISO, resulted in an intracellular Photofrin fluorescence signal comparable to that of the control cells, indicating the specificity of the pharmacological action. The pharmacological treatment seemed particularly effective with the aggregated species. This is suggested by the relative increase of the band at 670 nm, being greater than that in the 630 nm band in the emission spectra of Photofrin and PpIX, and by the comparison of the fluorescence intensity on cell homogenates measured both in the absence and in the presence of cetyltrimethyl-ammonium bromide as a detergent.

Partial characterization of a new virus from ranunculus with a divided RNA genome and circular supercoiled thread-like particles

An undescribed virus, here named ranunculus white mottle virus, was isolated in Italy from cultivated ranunculus showing mottle and distortion of leaves. The virus was mechanically transmissible to several herbaceous hosts. In negative stain, the particles appeared as circularised supercoiled threads 3 nm in diameter of different contour lengths; in some conditions the circles collapsed to form linear pseudobranched structures 9 nm in diameter. Immunolabeling of thin sections showed that viral antigen was widely distributed in the cytoplasm of parenchyma cells. The virus was not serologically related to the morphologically similar tenuiviruses, citrus psorosis-ringspot virus and tulip mild mottle mosaic virus. A major 43 kDa protein was present in purified preparations and in infected plant tissue, as also was a minor 28 kDa protein, serologically related to the major one. Nucleic acids extracted from purified particles consisted of at least three RNAs, of approximately 7.5, 1.8 and 1.5 kb, which appeared partly in single- and partly in double-stranded form. Purified preparations, but not viral RNAs, when mechanically inoculated, were infectious. Host range, tissue tropism, particle morphology and coat protein size place the virus closest to citrus psorosis-ringspot and tulip mild mottle mosaic viruses. These three viruses in turn show similarities with the Tenuiviruses and Bunyaviridae.

The effect of rescuer fatigue on the quality of chest compressions

OBJECTIVE

The aim of this study was to evaluate the influence of rescuer fatigue on the quality of chest compressions and the influence of the rescuer's gender, age, weight, height or professional status on the reduction of quality of chest compressions caused by fatigue.

MATERIAL AND METHODS

The study was carried out with the Laerdal Skillmeter Resusci Anne manikin. The participants were doctors and nurses who work in the Intensive Care and Emergency departments, with an age ranging from 25 to 45 years and trained in cardiopulmonary resuscitation (CPR). Statistical analysis of results includes analysis variance and three models of multiple linear regression.

RESULTS

Thirty-eight people took part in the experiment; 20 (52.6%) were females; 15 (39.5%) staff physicians, 15 (39.5%) nurses and eight residents. Mean age was 34.1 years (SD = 4.1). We found a significant reduction in correct compression performance over the course of time: in the first minute 79.7%, in the second 24.9%, in the third 18%, in the fourth 17.7% and in the last minute 18.5%. There were no differences related to the rescuer's gender or profession. The median interval until rescuers appreciated the effect of the fatigue on chest compressions quality was 186 s (SD = 84.1); that appreciation was not influenced by gender, age, weight, height or profession. There were no differences in the percentage of correct compressions related to gender (P = 0.07), insufficient sternal depression (P = 0.23) or total number of compressions in the first minute.

DISCUSSION

A decrease of compressions quality after the first minute of CPR is produced. This effect does not depend on gender, age, weight, height or rescuer's profession and it is not adequately perceived by the person who performs the chest compressions.

First Report of Moroccan Watermelon Mosaic Potyvirus in Zucchini in Italy

Unusual symptoms were observed in summer 1997 in field zucchini of several cultivars grown in central Italy. Symptoms included reduction in growth, severe mosaic, blistering and deformation of leaves, and malformation on fruits. Plants gave negative results in enzyme-linked immunosorbent assay (ELISA) for cucumber mosaic cucumovirus, squash mosaic comovirus, papaya ringspot, zucchini yellow fleck, zucchini yellow mosaic, and watermelon mosaic 2 potyviruses. Positive reactions were obtained in ELISA with a monoclonal antibody that reacts with many potyviruses (from J. Vetten, Braunschweig) and with polyclonal antibodies (Sanofi, France) to Moroccan watermelon mosaic potyvirus (MWMV). Field symptoms were reproduced in zucchini cvs. Genovese and Striato d'Italia by mechanical inoculation of samples from symptomatic field plants. Chenopodium amaranticolor, C. quinoa, and Gomphrena globosa gave local lesions, while Citrullus lanatus cv. Crimson Sweet, Cucumis melo cv. Top Mark, C. metuliferus, C. sativus cvs. Marketer, MM76, and Sweet Slice, and Cucurbita maxima reacted with systemic mosaic. C. melo cv. Doublon formed necrotic local lesions followed by systemic necrosis. No infection occurred in Nicotiana benthamiana, N. clevelandii, N. glutinosa, Phaseolus vulgaris cv. Black Turtle, Pisum sativum cv. Alaska, tobacco White Burley, and Vigna unguiculata. These data are in agreement with the known host range of MWMV. MWMV is a tentative species in the genus potyvirus, widely present in Africa and occasionally found in Spain (1,2). Further spread of this virus in the Mediterranean area will create new problems for commercial cucurbit production and breeding, and for diagnosis. References: (1) E. Kabelka and R. Grumet. Euphytica 95:237, 1997. (2) N. M. McKern et al. Arch. Virol. 131:467, 1993.

Resistance to tospoviruses in Nicotiana benthamiana transformed with the N gene of tomato spotted wilt virus: correlation between transgene expression and protection in primary transformants

Nicotiana benthamiana was transformed with the nucleoprotein (N) gene of an Italian isolate of tomato spotted wilt virus (TSWV). Forty-five T1 primary transformant lines were analyzed for the expression of N protein and for resistance to TSWV and three other tospoviruses: impatiens necrotic spot virus (INSV), groundnut bud necrosis virus (GBNV), and groundnut ringspot virus (GRSV). Thirteen of these lines were further characterized. Resistance to all TSWV isolates tested was found in two lines. The expression of the transgene (N mRNA) was lower in these resistant lines than in any of the susceptible lines, and the transgene N protein was either absent or present below detectable levels. These lines were susceptible to the other tospoviruses tested, but they developed symptoms milder than controls when inoculated with GRSV. Some of the lines producing high levels of N protein showed delays (of 2-3 weeks) in symptom expression with at least one of the TSWV isolates tested and symptom delay or attenuation with INSV or GRSV (or both). From our results it appears that high expression of TSWV N protein retards, in some cases, disease development by TSWV and INSV. In contrast, the lack of detectable expression of the transgenic N protein, accompanied by limited production of N transcripts, conferred TSWV-specific resistance.