Interleukin-12 can directly induce T-helper 1 responses in interferon-gamma (IFN-gamma) receptor-deficient mice, but requires IFN-gamma signalling to downregulate T-helper 2 responses

An in vivo model of pulmonary granuloma formation around embolized schistosome eggs was investigated as an environment in which to analyse a role for interleukin-12 (IL-12) in the differentiation of T-helper 1 (Th1) and Th2 subsets. Specifically, mice deficient for the interferon-γ receptor (IFN-γR−/–) were used to determine the role for IL-12 in the absence of IFN-γ-mediated signalling. We show that recombinant IL-12 administered to IFN-γR−/– mice caused the up-regulation of mRNA for IFN-γ in lung tissue, and the secretion of abundant IFN-γ by in vitro-cultured lymph node cells in response to egg antigens. This indicates that IL-12 can act independently of IFN-γ to induce the development of Th1 cells. Administration of rIL-12 to wild-type mice markedly reduced the secretion of Th2-associated cytokines, IL-4 and IL-5. However, these cytokines were not dramatically reduced in IFN-γR−/– mice treated with IL-12. We conclude that inhibition of these cytokines by IL-12 is primarily dependent upon effective IFN-γ signalling, although abrogation of T-cell derived IL-10 appeared to be dependent upon IL-12. We also show that increases in mRNA for the β2 subunit of the IL-12 receptor and the p40 subunit of IL-12 after rIL-12 treatment were lower in IFN-γR−/– mice, compared to wild-type mice, indicating that their expression was primarily dependent upon IFN-γ with only a minor role for IL-12

Patterns of bacterial diversity across a range of Antarctic terrestrial habitats

Although soil-borne bacteria represent the world's greatest source of biological diversity, it is not well understood whether extreme environmental conditions, such as those found in Antarctic habitats, result in reduced soil-borne microbial diversity. To address this issue, patterns of bacterial diversity were studied in soils sampled along a > 3200 km southern polar transect spanning a gradient of increased climate severity over 27° of latitude. Vegetated and fell-field plots were sampled at the Falkland (51°S), South Georgia (54°S), Signy (60°S) and Anchorage Islands (67°S), while bare frost-sorted soil polygons were examined at Fossil Bluff (71°S), Mars Oasis (72°S), Coal Nunatak (72°S) and the Ellsworth Mountains (78°S). Bacterial 16S rRNA gene sequences were recovered subsequent to direct DNA extraction from soil, polymerase chain reaction amplification and cloning. Although bacterial diversity was observed to decline with increased latitude, habitat-specific patterns appeared to also be important. Namely, a negative relationship was found between bacterial diversity and latitude for fell-field soils, but no such pattern was observed for vegetated sites. The Mars Oasis site, previously identified as a biodiversity hotspot within this region, proved exceptional within the study transect, with unusually high bacterial diversity. In independent analyses, geographical distance and vegetation cover were found to significantly influence bacterial community composition. These results provide insight into the factors shaping the composition of bacterial communities in Antarctic terrestrial habitats and support the notion that bacterial diversity declines with increased climatic severity