The use of complexes of lymphocyte antigens with antibody as immunogens for the preparation of antilymphocytic sera

Résumé Des complexes antigène-anticorps préparées par réaction du sérum antilymphocytaire (ALS) avec des lymphocytes ou avec des broyats lymphocytaires furent injectées aux lapins. Les ALS obtenu ainsi des lapins furent immunodépresseurs. Cette technique peut être utilisée pour obtenir des ALS plus specifique et moins toxique.

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Acknowlegments. We are indebted to our colleagues in the ALS Project Group of these Laboratories for much help and advice.     

The alkaloids ofAspidosperma neblinae. An application of a directly coupled gas chromatograph-mass spectrometer

Zusammenfassung Die Analyse der Basenfraktion vonAspidosperma neblinae mit Hilfe eines mit einem Massenspektrometer gekuppelten Gas-Chromatographen führte zur Identifizierung der folgenden Alkaloide: Aspidospermidin, 1, 2-Dehydroaspidospermidin, Deacetylpyrifolidin, 1, 2-Dehydrodeacetylpyrifolidin, Demethoxyaspidospermin, Aspidospermin, Demethylaspidospermin, Pyrifolidin, Aspidocarpin, Eburnamonin, und Neblinin.     

Transmission of cutaneous leishmaniasis by sand flies is enhanced by regurgitation of fPPG

Sand flies are the exclusive vectors of the protozoan parasite Leishmania, but the mechanism of transmission by fly bite has not been determined nor incorporated into experimental models of infection. In sand flies with mature Leishmania infections the anterior midgut is blocked by a gel of parasite origin, the promastigote secretory gel. Here we analyse the inocula from Leishmania mexicana-infected Lutzomyia longipalpis sand flies. Analysis revealed the size of the infectious dose, the underlying mechanism of parasite delivery by regurgitation, and the novel contribution made to infection by filamentous proteophosphoglycan (fPPG), a component of promastigote secretory gel found to accompany the parasites during transmission. Collectively these results have important implications for understanding the relationship between the parasite and its vector, the pathology of cutaneous leishmaniasis in humans and also the development of effective vaccines and drugs. These findings emphasize that to fully understand transmission of vector-borne diseases the interaction between the parasite, its vector and the mammalian host must be considered together.     

Mechanisms of gene silencing by double-stranded RNA

Double-stranded RNA (dsRNA) is an important regulator of gene expression in many eukaryotes. It triggers different types of gene silencing that are collectively referred to as RNA silencing or RNA interference. A key step in known silencing pathways is the processing of dsRNAs into short RNA duplexes of characteristic size and structure. These short dsRNAs guide RNA silencing by specific and distinct mechanisms. Many components of the RNA silencing machinery still need to be identified and characterized, but a more complete understanding of the process is imminent.     

Pilus chaperones represent a new type of protein-folding catalyst

Adhesive type 1 pili from uropathogenic Escherichia coli strains have a crucial role during infection by mediating the attachment to and potentially the invasion of host tissue. These filamentous, highly oligomeric protein complexes are assembled by the 'chaperone-usher' pathway, in which the individual pilus subunits fold in the bacterial periplasm and form stoichiometric complexes with a periplasmic chaperone molecule that is essential for pilus assembly. The chaperone subsequently delivers the subunits to an assembly platform (usher) in the outer membrane, which mediates subunit assembly and translocation to the cell surface. Here we show that the periplasmic type 1 pilus chaperone FimC binds non-native pilus subunits and accelerates folding of the subunit FimG by 100-fold. Moreover, we find that the FimC-FimG complex is formed quantitatively and very rapidly when folding of FimG is initiated in the presence of both FimC and the assembly-competent subunit FimF, even though the FimC-FimG complex is thermodynamically less stable than the FimF-FimG complex. FimC thus represents a previously unknown type of protein-folding catalyst, and simultaneously acts as a kinetic trap preventing spontaneous subunit assembly in the periplasm.     

Dynamic response of Permian brachiopod communities to long-term environmental change

The fossil record preserves numerous natural experiments that can shed light on the response of ecological communities to environmental change. However, directly observing the community dynamics of extinct organisms is not possible. As an alternative, neutral ecological models suggest that species abundance distributions reflect dynamical processes like migration, competition, recruitment, and extinction. Live-dead comparisons suggest that such distributions can be faithfully preserved in the rock record. Here we use a maximum-likelihood approach to show that brachiopod (lamp shell) abundance distributions from four temporally distinct ecological landscapes from the Glass Mountains, Texas (of the Permian period), exhibit significant differences. Further, all four are better fitted by zero-sum multinomial distributions, characteristic of Hubbell's neutral model, than by log-normal distributions, as predicted by the traditional ecological null hypothesis. Using the neutral model as a guide, we suggest that sea level fluctuations spanning about 10 Myr altered the degrees of isolation and exchange among local communities within these ecological landscapes. Neither these long-term environmental changes nor higher-frequency sea level fluctuations resulted in wholesale extinction or major innovation within evolutionary lineages.