Datation par le carbone 14 d'un niveau sédimentaire de l'archipel du lac Tchad

International audienceUne datation de 460 ans BP d'un niveau d'argile d'une carotte prélevée dans l'archipel du lac Tchad permet de situer une phase d'assèchement dans l'histoire récente du lac et de calculer une vitesse de sédimentation. Le rôle et l'importance des conditions locales sont soulignés

Problème du rajeunissement des sols issus de l'altération de roches volcaniques, par des éruptions récentes de cendres, aux Nouvelles-Hébrides et aux îles Canaries

Abstract. - Two soils, one from Aoba (New Hebrides), the other from Tenerife (Canarian Islands), the rejuvenation of which by a fall of volcanic ashes has been dated (by 14 C), show that, in a humid tropical or subtropical environment, the recent rejuvenation leads to pedological forms relatively less maturated than the normal soils type. In Aoba, they are one thousand years old, saturated and slighty evoluted andosols, in Tenerife appear andic brown earths that are less than 9000 years old and bury tropical paleosols. It is noteworthy in Aoba, that only one thousand years has been enough to form halloysite, whereas Aomine and Miyauchi (1963) estimated tah 8000 years have been necessary in the case of the Japanese andosols.Résumé. - Deux sols, l'un situé à Aoba (Nouvelles Hébrides), l'autre à Tenerife (Iles Canaries), dont le rajeunissement par un recouvrement de cendres volcaniques a été daté en âge absolu (par 14 C), montrent qu'en milieu tropical ou subtropical humide, le rajeunissement conduit à des formations pédologiques relativement moins évoluées que la normale. Dans le cas d'Aoba, il s'agit d'andosols saturés datant de mille ans environ ; dans celui de Tenerife, ce sont des sols bruns andiques âgés de moins de 9000 ans, recouvrant des paléosols tropicaux. Il est remarquable à Aoba, qu'un millier d'années a suffi, en milieu tropical humide pour l'apparition d'halloysite, alors qu'Aomine et Miyauchi (1963) estimaient qu'un laps de temps de 8000 ans était nécessaire dans le cas des andosols du Japon.Quantin Patrick, Fernandez-Caldas E., Guttierrez-Jerez F., Tejedor M.L., Delibrias G. Problème du rajeunissement des sols issus de l'altération de roches volcaniques par des éruptions récentes de cendres, aux Nouvelles-Hébrides et aux îles Canaries. In: Bulletin de l'Association de géographes français, N°426, 52e année, mai 1975. pp. 211-217

Complement protein C1q interacts with DC-SIGN via its globular domain, and thus may interfere with HIV-1 transmission

Dendritic Cells (DCs) are the most potent antigen presenting cells capable of priming naïve T cells. Its C-type lectin receptor, DC-SIGN, regulates a wide range of immune functions. Along with its role in HIV-1 pathogenesis through complement opsonization of the virus, DC-SIGN has recently emerged as an adaptor for complement protein C1q on the surface of immature DCs via a trimeric complex involving gC1qR, a receptor for the globular domain of C1q. Here, we have examined the nature of interaction between C1q and DC-SIGN in terms of domain localization, and implications of C1q-DC-SIGN-gC1qR complex formation on HIV-1 transmission. We first expressed and purified recombinant extracellular domains of DC-SIGN and its homologue SIGN-R as tetramers comprising of the entire extra cellular domain including the α-helical neck region, and monomers comprising of the carbohydrate recognition domain only. Direct binding studies revealed that both DC-SIGN and SIGN-R were able to bind independently to the recombinant globular head modules ghA, ghB and ghC, with ghB being the preferential binder. C1q appeared to interact with DC-SIGN or SIGN-R in a manner similar to IgG. Mutational analysis using single amino acid substitutions within the globular head modules showed that TyrB175 and LysB136 38 were critical for the C1q-DC-SIGN/SIGN-R interaction. Competitive studies revealed that gC1qR and ghB shared overlapping binding sites on DC-SIGN, implying that HIV- 1 transmission by DCs could be modulated due to the interplay of gC1qR-C1q with DC-SIGN. Since C1q, gC1qR and DC-SIGN can individually bind HIV-1, we examined how C1q and gC1qR modulated HIV-1-DC-SIGN interaction in an infection assay. Here, we report, for the first time, that C1q suppressed DC-SIGN-mediated transfer of HIV-1 to activated PBMCs, although the globular head modules did not. The protective effect of C1q was negated by the addition of gC1qR. In fact, gC1qR enhanced DC-SIGN-mediated HIV-1 transfer, suggesting its role in HIV-1 pathogenesis. Our results highlight the consequences of multiple innate immune pattern recognition molecules forming a complex that can modify their functions in a way which may be advantageous for the pathogen