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- Dandrea, T, et al.
(författare)
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Differential inhibition of inflammatory cytokine release from cultured alveolar macrophages from smokers and non-smokers by NO2
- 1997
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Ingår i: Human & experimental toxicology. - : SAGE Publications. - 0960-3271 .- 1477-0903. ; 16:10, s. 577-588
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Tidskriftsartikel (refereegranskat)abstract
- Human alveolar macrophages (AMs) obtained from smokers and non-smokers by bronchoalveolar lavage (BAL) were subjected to various concentrations of NO2 in an inverted monolayer exposure model. Culture super natants were collected 4 h after the exposure and assayed for secreted TNF-α, IL-1β, IL-8 and MIP-1α. The steady state levels of the mRNAs for these cytokines were also analysed in the cells. The adherence of BAL cells to plastic prior to exposure to the gas elevated the steady state mRNA levels of all four cytokines tested in smoker's cells and that of TNF-α and IL-1β, but not IL-8 (MIP-1α not tested), in non-smoker's cells. Interestingly, adherent cells from non-smokers released circa 15-, 3-,1.5- and 3-fold the amounts of IL-1β, IL-8, TNF-α and MIP-1α, respectively, than smoker's cells during control incubation or exposure to air. A 20 min exposure to NO2 (5 or 20 p.p.m.) did not increase the secretion of any of the cytokines from either cell type. In contrast, NO2 caused a concentration- dependent inhibition of the secretion of all cytokines except IL-1β from smoker's cells. Additionally, NO2 greatly diminished the release of all cytokines in response to further treatment with lipopolysaccharide (LPS). In contrast, only the secretion of TNF-α from non-smoker's cells was inhibited by the gas in a concentration- dependent manner, whilst LPS-induced secretion of the cytokines was not affected by the gas. The steady state levels of the respective mRNAs for each of the cytokines were not significantly affected in smoker's cells by exposure to NO2, except for a negative, dose-dependent trend in the case of TNF-α. Nitrogen dioxide also failed to elevate the levels of the mRNAs in non-smoker's cells but, again, tended to diminish the levels, particularly of IL-1β mRNA. However, exposure to the gas inhibited LPS- induced accumulation of cytokine mRNAs in smoker's cells only. The data suggest that macrophage-derived cytokine mediators of the sepsis response may not play a role in the generation of NO2-induced inflammation in the human lung. Conversely, the gas seems to non-specifically inhibit the release and/or production of cytokines, particularly from smoker's cells, at the post-transcrip tional level, and impairs the ability of the cells to increase the transcription and release of the cytokines in response to bacterial LPS. The fact that NO2 seriously impaired the already diminished capacity of smoker's cells to release several important pro-inflammatory cytokines, both under control conditions and in response to LPS, strongly suggest that the inhalation of NO2 in cigarette smoke may contribute to impairing host defence against infection in the lung.
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- Ohtani, S, et al.
(författare)
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Response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field
- 1997
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - 0148-0227. ; 102:A10, s. 22247-22260
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Tidskriftsartikel (refereegranskat)abstract
- The response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field (IMF) is examined with multi-instrument data from the Viking and DMSP-F7 satellites as well as ground magnetometer data. The event selected, which occurred on October 5, 1986, was previously identified as a high-latitude dayside form by Murphree and Elphinstone [1988]. IMF B-Y was positive during most of the Viking auroral UV observation, whereas IMF B-Z made a transient southward excursion, followed by a sharp increase to +8 nT. The results are summarized as follows: (1) There were two auroral belts extending westward from the early afternoon sector. The equatorward belt was persistent throughout the event and was embedded in the CPS/BPS precipitation region, whereas the poleward belt was in the open field line region and was associated with northward IMF B-Z. (2) A new auroral spot emerged in the afternoon sector just poleward of the previously active region, delayed 10 min from the sudden increase in IMF B-Z. This time lag is ascribed to the travel time of the new IMF orientation from the subsolar point to a solar wind-magnetosphere interaction site tailward of the dayside cusp, as well as to the response time of the dayside auroral acceleration process. (3) The new auroral activity expanded both eastward and westward during the first few minutes and then expanded primarily westward across the noon meridian, forming the poleward belt. The speed of the westward extension in the second phase was comparable to the speed of the ionospheric convection. (4) The dayside auroral process has a finite decay constant, which is inferred to be at least 10 min. (5) The response time of the midday ionospheric convection to IMF variations is estimated to be a few to several minutes.
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- Aikio, A T, et al.
(författare)
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On the origin of the high-altitude electric field fluctuations in the auroral zone
- 1996
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 101:A12, s. 27157-27170
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Tidskriftsartikel (refereegranskat)abstract
- Intense fluctuations in the electric field at high altitudes in the auroral zone are frequently measured by the Viking satellite. We have made an analysis of the origin of electric and magnetic fluctuations in the frequency range of 0.1 - 1 Hz by assuming four different sources for the signals: (I) spatial structures, (2) spatial structures with a parallel potential drop below the satellite, (3) traveling; shear Alfven waves, and (4) interfering shear Alfven waves. We will shaw that these different sources of the signals may produce similar amplitude ratios and phase differences between the perpendicular electric and magnetic fields. Since the different sources have different frequency dependencies, this can be used as an additional test if the signals are broadband. In other cases, additional information is needed, for example, satellite particle measurements or ground; magnetic measurements. The ideas presented in the theory were tested for one Viking eveningside pass over Scandinavia, where ground-based magnetometer and EISCAT radar measurements were available. The magnetic conditions were active during this pass and several interfering shear Alfven waves were found. Also, a spatial structure with a parallel potential drop below the satellite was identified. The magnitude of the 10-km-wide potential drop was at least 2 kV and the upward field-aligned current 26 mu A m(-2) (value mapped to the ionospheric level). The held-aligned conductance was estimated as 1.3 - 2.2x10(-8) S m(-2).
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- Andre, M, et al.
(författare)
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Ion energization mechanisms at 1700 km in the auroral region
- 1998
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - 0148-0227. ; 103:A3, s. 4199-4222
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Tidskriftsartikel (refereegranskat)abstract
- Observations obtained by the Freja satellite at altitudes around 1700 km in the high-latitude magnetosphere are used to study ion energization perpendicular to the geomagnetic field. Investigations of ions, electrons, plasma densities, electric and magnetic wave fields, and field-aligned currents are used to study O+ heating mechanisms. Three ion heating events are studied in detail, and 20 events are used in a detailed statistical study. More than 200 events are classified as belonging to one of four major types of ion heating and are ordered as a function of magnetic local time. The most common types of ion heating are associated with broadband low-frequency electric wave fields occurring at all local times. These waves cover frequencies from below one up to several hundred hertz and correspond to the most intense O+ energization. Heating by these waves at frequencies of the order of the O+ gyrofrequency at 25 Hz seems to be the important energization mechanism, causing O+ ion mean energies up to hundreds of eV. The broadband waves are associated with Alfven waves with frequencies up to at least a few hertz and with field-aligned currents. Other types of O+ energization events are less common. During these events the ions are heated by waves near the lower hybrid frequency or near half the proton gyrofrequency. These waves are generated by auroral electrons or in a few cases by precipitating ions.
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