Censoring of autoreactive B cell development by the pre-B cell receptor

Antibody diversity occurs randomly as B cells recombine their immunoglobulin (Ig) heavy- and light-chain genes during development. This process inevitably generates reactivity against self structures, and several mechanisms prevent the development of autoreactive B cells. We report here a role for the pre-B cell receptor, composed of Ig heavy and surrogate light chains, in the negative selection of cells expressing Ig heavy chains with the potential to generate autoantibodies. Surrogate light-chain-deficient (SLC-/-) mice harbored elevated levels of antinuclear antibodies (ANAs) in their serum and showed evidence of escape of pre-B cells expressing prototypic autoantibody heavy chains from negative selection, leading to mature autoantibody secreting CD21-CD23- B cells in the periphery. Thus, the pre-B cell receptor appears to censor the development of certain autoantibody-secreting cells and may represent an important factor in multifactorial autoimmune diseases.     

Kartoffelbau in Tirol II. Photosynthesevermögen und Respiration von verschiedenen Kartoffelsorten

Zusammenfassung Das Photosyntheseverm?gen der Kartoffelbl?tter h?ngt von der Beleuchtungsst?rke und Blattemperatur ab, das Optimum liegt zwischen 16 und 20°C. Die CO₂-Bindung ?ndert sich entsprechend dem Blattalter, so dass man physiologisch Jungbl?tter, erwachsene Bl?tter und Bl?tter im Abbauzustand unterscheiden muss. Erwachsene 2–3 Monate alte Bl?tter sind am leistungsf?higsten, assimilieren bei 10.000 Lux und 16°C um 30 mg CO₂, bei 50.000 Lux und 20°C 48–50 mg CO₂/g.h. Gelbgrün verf?rbte bl?tter leisten nur mehr 60–40%, Jungbl?tter etwa 60–80% obiger Werte. Die Blattatmung, die Atmung der Sprosse und Knollen sinkt mit der Reifung ab. Man kann den Stoffgewinn in monatlichen Bilanzübersichten aus Netto-Photosynthese und einzelnen Atmungskomponenten bestimmen. Monatsmittel um 17°C (mittlere Maxima um 23°C) sind für die Stoffproduktion optimal, Temperaturzunahme um 2°C (auf 19°C, 21°C) senkt den Reingewinn jeweils um 20–27%. Für Produktionsanalysen und Sortenbeurteilungen müsste neben dem Photosyntheseverm?gen vor allem die sortentypisch st?rker schwankende Blattfl?chenentwicklung und die Blattfl?chenandauer festgestellt werden.

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Summary The photosynthetic efficiency (— net photosynthesis in the presence of adequate water) of potato leaves depends on intensity of illumination and leaf temperature. The optimum temperature (at 10,000–50,000 Lux) lies between 16 and 20°C. CO₂ uptake varies considerably depending on the age of the leaves. One has, therefore, to distinguish between young, adult and senescent leaves on a physiological basis. Adult leaves, 2–3 months old, are the most efficient, giving a figure of 30 mg CO₂/g.h. at 10,000 Lux and 16–17°C, and 48–50 mg CO₂/g.h. at 50,000 Lux and 20°C. Yellowing leaves reach only 40–60% of these figures and young leaves 60–80% (Fig. 1–3). There is a close relationship between age and respiration level, the latter decreasing with maturity. Individual values for different temperatures are given in Tables 1–5. Dry matter production, because of its dependency on average monthly air temperature (monthly mean and mean maximum), can be determined by drawing up a monthly balance sheet of net photosynthesis and respiration loss. The optimum temperature for dry matter production is a monthly mean of 17° and a mean maximum of about 23°C. If the mean temperature increases to 19° (with a mean maximum of 25°) or 21° (with a mean maximum of 27°C), net production always decreases by about 20–27%. For production analysis and varietal evaluation, both leaf area development and duration, which vary greatly between varieties, must be determined in addition to photosynthetic efficiency.

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Résumé L'efficacité photosynthétique (photosynthèse nette avec des approvisionnements suffisants en eau) de feuilles de pomme de terre dépend de l'intensité de la lumière et de la température de le feuille. L'optimum de température se trouve entre 16 et 20°C (à 10.000, 50.000 Lux), le prélévement de CO₂ varie beaucoup et dépend de l'age de la feuille. Considérant la physiologie, on doit cependant faire la distinction entre feuilles jeunes, adultes et agées. Les feuilles adultes-vieilles de 2 à 3 mois- sont les plus actives à 10.000 Lux, 16–17°, 30 mg CO₂/g.h., à 50.000 Lux, 20° 48–50 mg CO₂/g.h. Les feuilles jaunissantes réagissent seulement de 40 à 60%; Les feuilles jeunes atteignent environ 60 à 80% des valeurs des feuilles les plus efficients (Fig. 1–3) en raison de leur importante respiration. La respiration des feuilles, bourgeons et tubercules dépend fortement de l'age; celle-ci décro?t avec la maturité (Tableau 1–5, valeurs individuelles à différentes températures). La production de matière sèche peut se calculer sur base de la photosynthèse nette mensuelle et les pertes par respiration sur base de leur dépendance de la température moyenne mensuelle (maxima moyens mensuels et température moyenne mensuelle). La température moyenne mensuelle de l'air de 17°C est optimale pour la production de matière sèche et les maxima moyens d'environ 23°C. Si les températures atteignent 19°C (maxima à 25°C) ou 21°C (maxima moyens 27°C) la production nette diminue toujours de 20 à 27%. Outre l'efficience photosynthétique, le développement foliaire et la durée des stades spécifiques—qui varient fortement avec les variétés—doivent être pris en considération pour l'analyse de la production et l'évaluation des variétés.

     

Differential Employment Patterns for Citizens and Non‐Citizens in Science and Engineering in the United States: Minting and Competitive Effects

ABSTRACT The consequences of the heavy inflow of foreign talent for U.S. scientists and engineers over the period 1973‐1997 are examined using data from the Survey of Doctorate Recipients. Of particular interest is whether non‐citizens trained in the United States have displaced citizens from jobs in science and engineering (S&E). Using a novel adaptation of the shift‐share technique, it is shown that citizen S&E doctorates have fewer jobs in S&E and fewer academic jobs than their non‐citizen counterparts for two reasons: the citizen doctoral population has experienced slower growth than the non‐citizen doctoral population, and citizen S&E doctorates have been displaced. Whether the displacement observed was a voluntary response of citizens to the lure of better opportunities elsewhere or an involuntary response indicative of having been pushed out by foreign talent remains to be determined.     

Zur Trendentwicklung des pH-Wertes des Niederschlags in Mitteleuropa

The trend development of the precipitation-pH in Central Europe Measurements of the precipitation-pH of the past five decades show practically no trend in central Europe. This result is confirmed by the absence of a yearly cycle of the pH-value although the SO₂-emissions in winter are nearly twice as high as in summer. Between the pH-value and the electrical conductivity as a measure of the dissolved material a characteristic relation exists yielding the relative saturation of the precipitation by acid. This relation, being similar for different sites, obviously describes the connection between the trace substance amount of the atmosphere and the overall scavenging capacity of the precipitation process. It also describes the limitation of the formation of acid. The point at which the removal capacity of acid was exhausted, was reached before 1940 in spite of further increasing emissions.     

Interaction of naphthalene derivatives with soil: an experimental and theoretical case study

This study provides insight into the relevance of the chemical functional groups of soil organic matter (aromatic, paraffinic, O‐alkyl, carboxyl and carbonyl carbon), as determined by CPMAS ¹³C NMR, on adsorption processes. Batch adsorption experiments with eight naphthalene derivatives were conducted with soils from a long‐term field experiment and model sorbents. Although the adsorption of some derivatives was mainly affected by the paraffinic organic carbon content in soil, the relation between the C‐distribution and adsorption was complex. This casts doubt on the use of such NMR data to estimate sorption behaviour. Additionally, sorption experiments were performed with six model sorbents representing typical soil components. Considerable adsorption of naphthalene derivatives was observed for montmorillonite and lignin; the smallest values were for kaolinite and cellulose. A quantum chemical approach was used to calculate a local polarity parameter as a molecular property of the naphthalene derivatives. This parameter was correlated with the logarithm of the adsorption coefficients, logK_d. Here, clear trends were observed for three of the model sorbents (kaolinite, montmorillonite and lignin).