Editors' Choice

Science  24 Jul 2009:
Vol. 325, Issue 5939, pp. 369
  1. Atmospheric Science

    An Eye for Ammonia

    1. H. Jesse Smith
    CREDIT: JUPITERIMAGES

    Ammonia is a trace gas of considerable importance for atmospheric chemistry, aerosol particle formation, and fertilization of the biosphere. Its global emissions have grown to more than twice their preindustrial values, mainly as a consequence of expanded agriculture and associated use of fertilizers. Yet large uncertainties in emissions budgets, due to the lack of adequate observational data, have hindered a confident assessment of the strengths of ammonia sources geographically. Clarisse et al. present infrared spectra obtained by satellite to map global atmospheric ammonia concentrations in 2008. They find that there is good qualitative agreement between these data and modeled values, but that large quantitative discrepancies exist, especially in regions above 30°N latitude. Additionally, they find a number of emission hot spots, all in the Northern Hemisphere, leading them to suggest that Northern Hemispheric ammonia emissions have been underestimated. These data, and this technique, should enhance our broader understanding of the global nitrogen cycle.

    Nat. Geosci. 2, 479 (2009).

  2. Systems Biology

    Figuring Out What to Aim At

    1. L. Bryan Ray

    A pervasive problem in identifying promising drug targets is that it can be difficult to ascertain which component of a complicated signaling network should be perturbed in order to produce the desired alteration of the system readout. Schoeberl et al. show the feasibility of a systems-level analysis for this purpose. Cancer is a known consequence of excessive signaling through the ErbB receptor tyrosine kinase family, which includes four related receptors and a dozen or so ligands (such as epidermal growth factor or EGF) that can act in various combinations. Their computational model suggested that binding to the ErbB3 receptor (which itself is mute with respect to kinase activity) with an affinity in the low nanomolar range in addition to disrupting binding by the ligand HRG1-β and signaling in response to the ligand betacellulin would be key. MM-121 is a monoclonal antibody with these in vitro attributes, and it also inhibited tumor xenografts in mice.

    Sci. Signal. 2, ra31 (2009).

  3. Chemistry

    Fate of Fluoropolymers

    1. Nicholas S. Wigginton

    The synthetic materials we rely on in everyday life are typically required to pass a series of laboratory tests before they can be used in consumer products. Outside the controlled environment of the lab, however, some approved compounds may degrade into potentially harmful byproducts. Washington et al. explored the capacity of a fluorotelomer polymer, similar to those commonly used in stain-resistant clothing and firefighting foam, to degrade into potentially toxic perfluorooctanoic acid when added to soil columns. In general, such studies face substantial challenges in unraveling the complex chemical and microbial pathways at play in real soil (often first-generation byproducts must be inferred from observation of their own induced by-products). Moreover, analysis of this specific type of degradation is hampered by the tendency of the byproduct to cling to the parent polymer and so elude sampling. The authors therefore developed a multistep extraction protocol involving the successive use of several different solvents. Their experiments yielded a degradation half-life on the order of 1000 years, consistent with prior studies; however, modeling of the data suggested great sensitivity of the kinetics to exposed surface area, potentially raising the degradation rate by two orders of magnitude for commercial polymers more finely grained than the authors' test samples. The exact degradation pathway remains unknown but could involve local microorganisms.

    Environ. Sci. Technol. 43, 10.1021/es9002668 (2009).

  4. Immunology

    No Accessories Needed

    1. Kristen L. Mueller

    In response to infection, CD4+ T cells differentiate into distinct effector subsets, which include T helper type 1 (TH1), TH2, TH17, and regulatory T cells. How do naïve T cells choose? The cells that present major histocompatibility complex (MHC) class II–bound antigens to T cells also deliver cues in the form of secreted cytokines that initiate lineage-specific differentiation programs. It has long been thought that dendritic cells are the bearers of this information, yet previous studies had found a limited activation of dendritic cells in response to TH2-inducing antigens and a lack of interleukin-4, which is the cytokine critical for directing TH2 cell differentiation.

    Basophil (blue) expressing interleukin-4 (green) and MHC II (red).CREDIT: PERRIGOUE AND YOSHIMOTO

    Perrigoue et al., Yoshimoto et al., and Sokol et al. show that for TH2 CD4+ T cells—which mediate responses to parasitic helminths, protease allergens, and allergy-inducing immune complexes—basophils, rather than dendritic cells, are the antigen-presenting cells that initiate TH2 cell responses in mice. These studies push basophils into the limelight and will potentially lead to further understanding of allergic reactions.

    Nat. Immunol. 10, 697; 706; 713 (2009).