Isabelle Dumont

Effect of Vitamin C Supplements on Cell-Mediated Immunity in Old People

Both ageing and vitamin C (VC) deficiency result in immune defect. Since low serum and tissue levels of VC are found in the elderly, we have in a placebo-controlled study, tested the effect of VC supplements (500 mg/day i.m. for 1 month) on various immune parameters. Indeed, VC enhances the proliferative response of T lymphocytes in vitro, and the tuberculin skin hypersensitivity in vivo. Neither the serum concentrations of IgA, IgG and IgM, nor the proportion of E-rosette-forming cells were modified. No significant change was observed in the placebo-treated group.

High-resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first-year sea ice at Ice Station Polarstern, western Weddell Sea, Antarctica

High-resolution profiles of ice dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer-level first-year sea ice throughout December 2004 during the Ice Station Polarstern drift experiment (western Weddell Sea, Antarctica). Ice DMSP and DMS concentrations were always maximum at the bottom of the ice sheet (636-2627 and 292-1430 nM, respectively) where the highest chlorophyll a levels were also found (15-30 μg L-1). Throughout the observation period, the autotrophic surface community (32-205 μg C L-1) was dominated by Phaeocystis sp. while the bottom community (1622-3830 μg C L -1) mainly consisted of pennate diatoms. This illustrates that, although being known for lower DMSP-to-chlorophyll a ratios than Phaeocystis sp., diatoms dominated the overall DMSP production because of their much larger biomass. Decreasing DMSP concentrations and increasing DMS-to-DMSP ratios in the bottom layers with time suggested active DMSP-to-DMS conversion in a slowly degrading environment. Drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact (1) the migration of DMSP and DMS through the brine network, (2) the DMSP-to-DMS conversion processes within the ice interior, and (3) the physiological response of the ice algae. First-order flux estimates show that decaying summer-level first-year sea ice alone can significantly contribute to the regional sulfur budget of the Weddell Sea with an estimated average loss rate of 5.7 mol DMS(P) m-2 d-1) toward the atmosphere and the ocean. Copyright 2010 by the American Geophysical Union.