Dendritic cells (DC) mediate airway Ag presentation and play key roles in asthma and infections. Although DC subsets are known to perform different functions, their occurrence in mouse lungs has not been clearly defined. In this study, three major lung DC populations have been found. Two of them are the myeloid and plasmacytoid DC (PDC) well-characterized in other lymphoid organs. The third and largest DC population is the integrin αE (CD103) β7-positive and I-AhighCD11chigh-DC population. This population was found to reside in the lung mucosa and the vascular wall, express a wide variety of adhesion and costimulation molecules, endocytose avidly, present Ag efficiently, and produce IL-12. Integrin αEβ7+ DC (αE-DC) were distinct from intraepithelial lymphocytes and distinguishable from CD11bhigh myeloid and mPDCA-1+B220+Gr-1+ PDC populations in surface marker phenotype, cellular functions, and tissue localization. Importantly, this epithelial DC population expressed high levels of the Langerhans cell marker Langerin and the tight junction proteins Claudin-1, Claudin-7, and ZO-2. In mice with induced airway hyperresponsiveness and eosinophilia, αE-DC numbers were increased in lungs, and their costimulation and adhesion molecules were up-regulated. These studies show that αE-DC is a major and distinct lung DC population and a prime candidate APC with the requisite surface proteins for migrating across the airway epithelia for Ag and pathogen capture, transport, and presentation. They exhibit an activated phenotype in allergen-induced lung inflammation and may play significant roles in asthma pathogenesis.

Lung CD11chigh dendritic cells (DC) are comprised of two major phenotypically distinct populations, the CD11bhigh DC and the integrin αEβ7+ DC (CD103+ DC). To examine whether they are functionally distinguishable, global microarray studies and real-time PCR analysis were performed. Significant differences between the two major CD11chigh DC types in chemokine mRNA expression were found. CD11bhigh DC is a major secretory cell type and highly expressed at least 16 chemokine mRNA in the homeostatic state, whereas CD103+ DC highly expressed only 6. Intracellular chemokine staining of CD11chigh lung cells including macrophages, and ELISA determination of sort-purified CD11chigh cell culture supernatants, further showed that CD11bhigh DC produced the highest levels of 9 of 14 and 5 of 7 chemokines studied, respectively. Upon LPS stimulation in vitro and in vivo, CD11bhigh DC remained the highest producer of 7 of 10 of the most highly produced chemokines. Induction of airway hyperreactivity and lung inflammation increased lung CD11bhigh DC numbers markedly, and they produced comparable or higher amounts of 11 of 12 major chemokines when compared with macrophages. Although not a major producer, CD103+ DC produced the highest amounts of the Th2-stimulating chemokines CCL17/thymus and activation-related chemokine and CCL22/monocyte-derived chemokine in both homeostasis and inflammation. Significantly, CCL22/monocyte-derived chemokine exhibited regulatory effects on CD4+ T cell proliferation. Further functional analysis showed that both DC types induced comparable Th subset development. These studies showed that lung CD11bhigh DC is one of the most important leukocyte types in chemokine production and it is readily distinguishable from CD103+ DC in this secretory function.

We tested the hypotheses that benthic macroinvertebrates, especially chironomid larvae in the Tribe Chironomini, from small oligotrophic arctic lakes are only weakly linked to pelagic food sources, and that they are trophically linked to biogenic methane. All offshore benthic macroinvertebrates sampled from 20 lakes were depleted in 13 C compared with nearshore benthic macroinvertebrates. Nearshore macroinvertebrates had ␦ 13 C consistent with feeding on periphyton and/or terrestrial detritus. However, ␦ 13 C of offshore Chironomini, the dominant macroinvertebrate group, and oligochaetes, was more depleted than that of other offshore macroinvertebrates to a degree that could only be explained by a diet that included carbon derived from biogenic methane. Seston ␦ 13 C showed a small shift toward greater depletion in deeper lakes, but ␦ 13 C of Chironomini, oligochaetes, and predatory chironomids varied as a function of dissolved oxygen concentration (DO) at the sediment-water interface, which was generally lower in shallow lakes that were deep enough to stratify. In lakes with lower DO in bottom waters, the importance of methane-based carbon to Chironomini was greater. Experimental 15 N enrichment of phytoplankton in small-and mid-sized arctic lakes resulted in limited 15 N enrichment of most benthic macroinvertebrates, indicating that their productivity was not closely tied to pelagic production. It is likely that aerobic benthic metabolism of dissolved organic carbon (DOC) also is an important energy source for benthic macroinvertebrates in sediments because the link between benthic macroinvertebrate production and contemporary pelagic primary production was weak regardless of dependence on biogenic methane.

1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape-level factors that control colonisation and extinction. 2. We used classification and regression tree (CART) analyses to quantify the importance of landscape-level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables). 3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied with species. Extinction variables were most important for lake trout (Salvelinus namaycush) and slimy sculpin (Cottus cognatus), a mixture of extinction and colonisation variables was important for arctic char (Salvelinus alpinus), and colonisation variables were most important for arctic grayling (Thymallus arcticus) and round whitefish (Prosopium cylindraceum). 4. Ecological differences among species account for much of the difference in relative importance of colonisation versus extinction variables. In addition, stream piracy events have occurred over geologic time scales, which have resulted in lakes that are currently inaccessible but support relict fish populations. 5. Climate warming, currently occurring in the arctic, is likely to alter further the stream network, which could have dramatic effects on fish distributions by affecting access to isolated lakes or isolating lakes that are currently accessible.

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