Résumé Étude comparative des proprietés biologiques des anticorps IgM, IgG1 et IgG2 du rat. Les résultats montrent que le pouvoir agglutinant et lytique des anticorps IgM est respectivement 37 et 100 fois supérieur à celui des deux classes d'anticorps IgG. Par contre, en ce qui concerne le phénomène d'Arthus, les anticorps IgM sont moins actifs que les anticorps IgG, si les rapports sont exprimés en poids. Si l'on calcule les rapports par nombre de molécules, les anticorps IgM sont aussi, dans ce cas, plus actifs que les IgG. 相似文献
Assessing the conditions under which magmas become fluid-saturated has important bearings on the geochemical modelling of magmas because volatile exsolution may profoundly alter the behaviour of certain trace elements that are strongly partitioned in the coexisting fluid. Saal et al. report primitive melt inclusions from dredged oceanic basalts of the Siqueiros transform fault, from which they derive volatile abundances of the depleted mantle, based on the demonstration that magmas are not fluid-saturated at their eruption depth and so preserve the mantle signature in terms of their volatile contents. However, in their analysis, Saal et al. consider only fluid-melt equilibria, and do not take into account the homogeneous equilibria between fluid species, which, as we show here, may lead to a significant underestimation of the pressure depth of fluid saturation. 相似文献
Volatiles carried by magmas, either dissolved or exsolved, have a fundamental effect on a variety of geological phenomena, such as magma dynamics and the composition of the Earth's atmosphere. In particular, the redox state of volcanic gases emanating at the Earth's surface is widely believed to mirror that of the magma source, and is thought to have exerted a first-order control on the secular evolution of atmospheric oxygen. Oxygen fugacity (f(O2) estimated from lava or related gas chemistry, however, may vary by as much as one log unit, and the reason for such differences remains obscure. Here we use a coupled chemical-physical model of conduit flow to show that the redox state evolution of an ascending magma, and thus of its coexisting gas phase, is strongly dependent on both the composition and the amount of gas in the reservoir. Magmas with no sulphur show a systematic f(O2) increase during ascent, by as much as 2 log units. Magmas with sulphur show also a change of redox state during ascent, but the direction of change depends on the initial f(O2) in the reservoir. Our calculations closely reproduce the H2S/SO2 ratios of volcanic gases observed at convergent settings, yet the difference between f(O2) in the reservoir and that at the exit of the volcanic conduit may be as much as 1.5 log units. Thus, the redox state of erupted magmas is not necessarily a good proxy of the redox state of the gases they emit. Our findings may require re-evaluation of models aimed at quantifying the role of magmatic volatiles in geological processes. 相似文献
Noonan syndrome is a developmental disorder characterized by short stature, facial dysmorphia, congenital heart defects and skeletal anomalies. Increased RAS-mitogen-activated protein kinase (MAPK) signaling due to PTPN11 and KRAS mutations causes 50% of cases of Noonan syndrome. Here, we report that 22 of 129 individuals with Noonan syndrome without PTPN11 or KRAS mutation have missense mutations in SOS1, which encodes a RAS-specific guanine nucleotide exchange factor. SOS1 mutations cluster at codons encoding residues implicated in the maintenance of SOS1 in its autoinhibited form. In addition, ectopic expression of two Noonan syndrome-associated mutants induces enhanced RAS and ERK activation. The phenotype associated with SOS1 defects lies within the Noonan syndrome spectrum but is distinctive, with a high prevalence of ectodermal abnormalities but generally normal development and linear growth. Our findings implicate gain-of-function mutations in a RAS guanine nucleotide exchange factor in disease for the first time and define a new mechanism by which upregulation of the RAS pathway can profoundly change human development. 相似文献
We evaluated the energy metabolism of human mesenchymal stem cells (MSC) isolated from umbilical cord (UC) of preterm (< 37 weeks of gestational age) and term (≥ 37 weeks of gestational age) newborns, using MSC from adult bone marrow as control. A metabolic switch has been observed around the 34th week of gestational age from a prevalently anaerobic glycolysis to the oxidative phosphorylation. This metabolic change is associated with the organization of mitochondria reticulum: preterm MSCs presented a scarcely organized mitochondrial reticulum and low expression of proteins involved in the mitochondrial fission/fusion, compared to term MSCs. These changes seem governed by the expression of CLUH, a cytosolic messenger RNA-binding protein involved in the mitochondria biogenesis and distribution inside the cell; in fact, CLUH silencing in term MSC determined a metabolic fingerprint similar to that of preterm MSC. Our study discloses novel information on the production of energy and mitochondrial organization and function, during the passage from fetal to adult life, providing useful information for the management of preterm birth. 相似文献
This paper explores Checkland’s Soft Systems Methodology (SSM) through the lenses of a theoretical framework that incorporates key concepts from Maturana’s Ontology of the Observer (OoO) with the view of complementing Checkland’s SSM application process. We outline and examine paradigmatic compatibility between: Checkland’s ontological position (reality is problematic/chaotic) together with his interpretivist epistemology (multiple perceptions enrich the ever-changing reality); and Maturana’s OoO (we are immersed in the praxis of living in an ontological multi-universe). We argue that OoO resonates with key SSM theoretical underpinnings. After establishing compatibility between these two influential systems thinkers, we advance a conceptual framework in which Checkland’s SSM learning process is re-visited through a the framework grounded on Maturana’s OoO. The proposed framework illustrates how key ideas drawn from Maturana’s OoO can shed light into the way in which some of the main SSM devices (i.e.: Root definitions, Conceptual model) are used in the SSM process. By doing that, SSM is enriched and becomes more flexible as the stakeholders involved are placed within the domain of constitutive ontologies from which, a deeper dialogue can be promoted in a domain of coexistence in mutual acceptance. We argue that this is a suitable way to have more flexible and holistic views for a SSM intervention in particular to promote the learning process and debating proposed changes amongst the stakeholders involved. The proposed framework, when applied, may enhance the power of SSM learning process and when adopted can have substantial implications to complement the SSM process.