5,305 research outputs found
Involvement of Thyroid Hormones in the Expression of MHC class I Antigens During Ontogeny in Xenopus
The major histocompatibility complex (MHC) is a cluster of genes encoding products central
to all major functions of the vertebrate immune system. Evidence for an MHC can be found
in all vertebrate groups that have been examined except the jawless fishes. Expression of
MHC class I and class II antigens early in ontogeny is critically important for development
of T lymphocytes capable of discriminating self from nonself. Because of this essential role
in T-cell development, the ontogeny of MHC expression in the South African clawed frog,
Xenopus laevis, was studied. Previous studies of MHC class I expression in Xenopus laevis suggested that class I antigens are virtually absent from tadpole tissues until climax of metamorphosis.
We therefore examined the possible role of thyroid hormones (TH) in the induction
of class I. By flow cytometry, a small amount of class I expression was detectable on
splenocytes and erythrocytes in untreated frogs at prometamorphic stages 55-58, and the
amount increased significantly at the conclusion of metamorphic climax. Thus, metamorphosis
is associated with increased intensity of class I expression. Neither inhibition nor acceleration
of metamorphosis altered the timing of onset of class I expression. However, inhibition
of metamorphosis prevented the increase in class I expression characteristic of adult
cell populations. Because expression was not accelerated in TH-treated frogs or delayed in
metamorphosis-inhibited frogs, it is unlikely that TH are the direct developmental cues that
induce expression, although they seem to be required for the upregulation of class I expression
occurring at metamorphosis. Differences in the pattern of expression in different subpopulations
of cells suggest a complex pattern of regulation of expression of class I antigens
during ontogeny
Involvement of Thyroid Hormones in the Expression of MHC class I Antigens During Ontogeny in Xenopus
The major histocompatibility complex (MHC) is a cluster of genes encoding products central
to all major functions of the vertebrate immune system. Evidence for an MHC can be found
in all vertebrate groups that have been examined except the jawless fishes. Expression of
MHC class I and class II antigens early in ontogeny is critically important for development
of T lymphocytes capable of discriminating self from nonself. Because of this essential role
in T-cell development, the ontogeny of MHC expression in the South African clawed frog,
Xenopus laevis, was studied. Previous studies of MHC class I expression in Xenopus laevis suggested that class I antigens are virtually absent from tadpole tissues until climax of metamorphosis.
We therefore examined the possible role of thyroid hormones (TH) in the induction
of class I. By flow cytometry, a small amount of class I expression was detectable on
splenocytes and erythrocytes in untreated frogs at prometamorphic stages 55-58, and the
amount increased significantly at the conclusion of metamorphic climax. Thus, metamorphosis
is associated with increased intensity of class I expression. Neither inhibition nor acceleration
of metamorphosis altered the timing of onset of class I expression. However, inhibition
of metamorphosis prevented the increase in class I expression characteristic of adult
cell populations. Because expression was not accelerated in TH-treated frogs or delayed in
metamorphosis-inhibited frogs, it is unlikely that TH are the direct developmental cues that
induce expression, although they seem to be required for the upregulation of class I expression
occurring at metamorphosis. Differences in the pattern of expression in different subpopulations
of cells suggest a complex pattern of regulation of expression of class I antigens
during ontogeny
The Impact of Menthol Cigarettes on Smoking Initiation among Non-Smoking Young Females in Japan
Japan presents an excellent case-study of a nation with low female smoking rates and a negligible menthol market which changed after the cigarette market was opened to foreign competition. Internal tobacco industry documents demonstrate the intent of tobacco manufacturers to increase initiation among young females through development and marketing of menthol brands. Japanese menthol market share rose rapidly from less than 1% in 1980 to 20% in 2008. Menthol brand use was dominated by younger and female smokers, in contrast with non-menthol brands which were used primarily by male smokers. Nationally representative surveys confirm industry surveys of brand use and provide further evidence of the end results of the tobacco industryâs actionsâincreased female smoking in Japan. These findings suggest that female populations may be encouraged to initiate into smoking, particularly in developing nations or where female smoking rates remain low, if the tobacco industry can successfully tailor brands to them. The Japanese experience provides a warning to public health officials who wish to prevent smoking initiation among young females
Disease prevention strategies for QX disease (Marteilia sydneyi) of Sydney rock oysters (Saccostrea glomerata)
The Sydney rock oyster (Saccostrea glomerata) forms the basis of an important aquaculture industry on the east coast of Australia. During the 1970s, production of S. glomerata began to decline, in part as a result of mortalities arising from Queensland unknown (QX) disease. Histological studies implicated the paramyxean parasite Marteilia sydneyi in the disease outbreaks. Disease zoning was implemented to prevent the spread of M. sydneyi-infected oysters. This control measure hindered rock oyster farming, which historically has relied on transferring wild-caught spat between estuaries for on-growing to market size and has not prevented the subsequent occurrence of QX disease in the Georges and Hawkesbury rivers in central New South Wales. Management of QX disease has been hampered by the complicated life cycle of M. sydneyi, with outbreaks of QX disease likely to be regulated by a combination of the abundance of intermediate host of M. sydneyi, environmental stressors, and the immunocompetence of S. glomerata. The future of the Sydney rock oyster industry relies on understanding these factors and progressing the industry from relying on farming wild-caught seed to the successful commercialization of hatchery-produced QX-resistant S. glomerata
Probing the Balance of AGN and Star-Forming Activity in the Local Universe with ChaMP
The combination of the SDSS and the Chandra Multiwavelength Project (ChaMP)
currently offers the largest and most homogeneously selected sample of nearby
galaxies for investigating the relation between X-ray nuclear emission, nebular
line-emission, black hole masses, and properties of the associated stellar
populations. We present here novel constraints that both X-ray luminosity Lx
and X-ray spectral energy distribution bring to the galaxy evolutionary
sequence H II -> Seyfert/Transition Object -> LINER -> Passive suggested by
optical data. In particular, we show that both Lx and Gamma, the slope of the
power-law that best fits the 0.5 - 8 keV spectra, are consistent with a clear
decline in the accretion power along the sequence, corresponding to a softening
of their spectra. This implies that, at z ~ 0, or at low luminosity AGN levels,
there is an anti-correlation between Gamma and L/Ledd, opposite to the trend
exhibited by high z AGN (quasars). The turning point in the Gamma -L/Ledd LLAGN
+ quasars relation occurs near Gamma ~ 1.5 and L/Ledd ~ 0.01. Interestingly,
this is identical to what stellar mass X-ray binaries exhibit, indicating that
we have probably found the first empirical evidence for an intrinsic switch in
the accretion mode, from advection-dominated flows to standard (disk/corona)
accretion modes in supermassive black hole accretors, similar to what has been
seen and proposed to happen in stellar mass black hole systems. The
anti-correlation we find between Gamma and L/Ledd may instead indicate that
stronger accretion correlates with greater absorption. Therefore the trend for
softer spectra toward more luminous, high redshift, and strongly accreting
AGN/quasars could simply be the result of strong selection biases reflected in
the dearth of type 2 quasar detections.Comment: 23 pages, 8 figures, 1 long (3 page) table, to appear in Ap
Search for quarks in cosmic rays with the Leeds cloud chamber
The central regions of cosmic-ray air showers near sea level have been studied with the Leeds cloud chamber for the possible occurrence of low-ionizing tracks. The average energy of the primary particles was a few times 106 GeV. Our current results give an upper limit to the "flux" of quarks of 1.2 x 10-11 cm-2 sec-1 sr-1 at a 90% confidence level. A simple model is used to obtain an upper limit to the production cross section versus quark mass.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21994/1/0000406.pd
A Multiwavelength Study of Binary Quasars and Their Environments
We present Chandra X-ray imaging and spectroscopy for 14 quasars in spatially
resolved pairs, part of a complete sample of binary quasars with small
transverse separations drawn from Sloan Digital Sky Survey (DR6) photometry. We
find no significant difference in X-ray properties when compared with large
control samples of isolated quasars. We present infrared photometry from our
observations with SWIRC at the MMT, and from the WISE Preliminary Data Release,
and fit simple spectral energy distributions to all 14 QSOs. We find
preliminary evidence that substantial contributions from star formation are
required, but possibly no more so than for isolated X-ray-detected QSOs.
Sensitive searches of the X-ray images for extended emission, and the optical
images for optical galaxy excess show that these binary QSOs are not
preferentially found in rich cluster environments. While larger binary QSO
samples with richer far-IR and sub-millimeter multiwavelength data might better
reveal signatures of merging and triggering, optical color-selection of QSO
pairs may be biased against such signatures. X-ray and/or variability selection
of QSO pairs, while challenging, should be attempted. We present in our
Appendix a primer on X-ray flux and luminosity calculations.Comment: 21 pages, accepted to ApJ 08/31/201
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