IgG1 hypergammaglobulinaemia in chronic parasitic infections in mice: magnitude of the response in mice infected with various parasites

Mice chronically infected with 3 metazoan and 1 protozoan parasite contain in their circulation levels of IgG1 which are increased over the levels in uninfected mice by at least 10x. In the case of infection with the larval cestode, Mesocestoides corti, the serum IgG1 concentration can reach greater than 50 mg/ml and, with a half-life of less than 2 days, the number of cells engaged in IgG1 production is approximately 2 x 10(8). The IgG1 hypergammaglobulinaemia is not seen in infected hypothymic nude mice. Biosynthetic labelling studies with organ and tissue cultures established that in two of the chronic infections the organs principally involved in IgG1 synthesis were those pathologically involved or those "in line" for antigen capture: i.e. liver and spleen in the case of M. corti which is located in the liver and the peritoneal cavity, and various intestinal lymph nodes in the case of the gut-dwelling nematode, Nematospiroides dubius. This apparently exaggerated response to chronic parasitic infection is of interest simply because of the potential magnitude of the effect and the fact that it involves an Ig isotype with very poorly defined biological function.     

Comprehensive genotyping of the USA national maize inbred seed bank

Background

Genotyping by sequencing, a new low-cost, high-throughput sequencing technology was used to genotype 2,815 maize inbred accessions, preserved mostly at the National Plant Germplasm System in the USA. The collection includes inbred lines from breeding programs all over the world.

Results

The method produced 681,257 single-nucleotide polymorphism (SNP) markers distributed across the entire genome, with the ability to detect rare alleles at high confidence levels. More than half of the SNPs in the collection are rare. Although most rare alleles have been incorporated into public temperate breeding programs, only a modest amount of the available diversity is present in the commercial germplasm. Analysis of genetic distances shows population stratification, including a small number of large clusters centered on key lines. Nevertheless, an average fixation index of 0.06 indicates moderate differentiation between the three major maize subpopulations. Linkage disequilibrium (LD) decays very rapidly, but the extent of LD is highly dependent on the particular group of germplasm and region of the genome. The utility of these data for performing genome-wide association studies was tested with two simply inherited traits and one complex trait. We identified trait associations at SNPs very close to known candidate genes for kernel color, sweet corn, and flowering time; however, results suggest that more SNPs are needed to better explore the genetic architecture of complex traits.

Conclusions

The genotypic information described here allows this publicly available panel to be exploited by researchers facing the challenges of sustainable agriculture through better knowledge of the nature of genetic diversity.     

The effects of sediment desiccation on the potential for nitrification, denitrification, and methanogenesis in an Australian reservoir

Sediments from an Australian reservoir were selected for varying degrees of in situ desiccation (i.e. non-desiccated, partially desiccated and desiccated). Sediment samples were then chemically amended with appropriate electron donors and acceptors to ascertain the effect of sediment desiccation on the potential for nitrification, denitrification, methanogenesis, and the interaction of these processes. There was no detectable nitrification in these sediments yet up to 75% of added nitrate was converted to dinitrogen. Denitrification was predominantly limited by nitrate although there was evidence of carbon co-limitation. None of the nitrogen cycle processes were notably affected by sediment desiccation. There was no flush of mineral nitrogen from desiccated sediments upon rewetting. Methanogenesis did not begin in these sediments until nitrate concentrations fell below 2.25 * 10^-5 M. Methanogenesis was always carbon limited. Methanogens were affected by sediment desiccation but were capable of recovery over time upon rewetting of sediments.