Cultivar‐specific effects of pathogen testing on storage root yield of sweetpotato,Ipomoea batatas

The accumulation and perpetuation of viral pathogens over generations of clonal propagation in crop species such as sweetpotato, Ipomoea batatas, inevitably result in a reduction in crop yield and quality. This study was conducted at Bundaberg, Australia to compare the productivity of field‐derived and pathogen‐tested (PT) clones of 14 sweetpotato cultivars and the yield benefits of using healthy planting materials. The field‐derived clonal materials were exposed to the endemic viruses, while the PT clones were subjected to thermotherapy and meristem‐tip culture to eliminate viral pathogens. The plants were indexed for viruses using nitrocellulose membrane‐enzyme‐linked immunosorbent assay and graft‐inoculations onto Ipomoea setosa. A net benefit of 38% in storage root yield was realised from using PT materials in this study. Conversely, in a similar study previously conducted at Kerevat, Papua New Guinea (PNG), a net deficit of 36% was realised. This reinforced our finding that the response to pathogen testing was cultivar dependent and that the PNG cultivars in these studies generally exhibited increased tolerance to the endemic viruses present at the respective trial sites as manifested in their lack of response from the use of PT clones. They may be useful sources for future resistance breeding efforts. Nonetheless, the potential economic gain from using PT stocks necessitates the use of pathogen testing on virus‐susceptible commercial cultivars.     

Class II MHC molecules are present in macrophage lysosomes and phagolysosomes that function in the phagocytic processing of Listeria monocytogenes for presentation to T cells.

Phagocytic processing of heat-killed Listeria monocytogenes by peritoneal macrophages resulted in degradation of these bacteria in phagolysosomal compartments and processing of bacterial antigens for presentation to T cells by class II MHC molecules. Within 20 min of uptake by macrophages, Listeria peptide antigens were expressed on surface class II MHC molecules, capable of stimulating Listeria-specific T cells. Within this period, degradation of labeled bacteria to acid-soluble low molecular weight catabolites also commenced. Immunoelectron microscopy was used to evaluate the compartments involved in this processing. Upon uptake of the bacteria, phagosomes containing Listeria fused rapidly with both lysosomes and endosomes. Class II MHC molecules were present in a tubulo-vesicular lysosome compartment, which appeared to fuse with phagosomes, as well as in the resulting phagolysosomes containing internalized Listeria; these compartments were all positive for Lamp 1 and cathepsin D and lacked 46-kD mannose-6-phosphate receptors. In addition, class II MHC and Lamp 1 were co-localized in vesicles of the trans Golgi reticulum, where they were segregated from 46-kD mannose-6-phosphate receptors. Vesicles containing both Listeria-derived components and class II MHC molecules were also observed; some of these may represent vesicles recycling from phagolysosomes, potentially bearing processed immunogenic peptides complexed with class II MHC. These results support a central role for lysosomes and phagolysosomes in the processing of bacterial antigens for presentation to T cells. Tubulo-vesicular lysosomes appear to represent an important convergence of endocytic, phagocytic and biosynthetic pathways, where antigens may be processed to allow binding to class II MHC molecules and recycling to the cell surface.     

The effects of an aromatization inhibitor on the reproductive behavior of male zebra finches

Recent evidence indicates that aromatizable androgens are more effective than nonaromatizable androgens in restoring normal levels of sexual behavior in castrated male zebra finches (Poephila guttata). To determine whether the efficacy of treatment with aromatizable androgens, is in part due to their conversion to estrogens, castrated male finches were treated with androstenedione (AE), an aromatizable androgen, and their sexual and aggressive behavior was compared with that of castrates treated with AE plus 1,4,6-androstatriene-3,17-dione (ATD), an aromatization inhibitor. Males treated with AE + ATD showed less courtship activity and less copulatory behavior than AE-treated males, and were unlikely to have nests. Estradiol (E), when given concurrently with AE + ATD, reversed the inhibitory effects of ATD and restored levels of courtship and copulation to those observed in AE-treated males. Only AE- and AE + ATD + E-treated males displayed aggressive behaviors, but the frequency of such behaviors was so low that there were no significant differences across groups. These data affirm the importance of estrogen in the control of reproductive activities in male zebra finches and indicate that aromatization may be an obligatory step for maintaining normal levels of sexual and aggressive behavior.     

Bacterial heat shock proteins enhance class II MHC antigen processing and presentation of chaperoned peptides to CD4+ T cells

APCs process heat shock protein (HSP):peptide complexes to present HSP-chaperoned peptides on class I MHC molecules, but the ability of HSPs to contribute chaperoned peptides for class II MHC (MHC-II) Ag processing and presentation is unclear. Our studies revealed that exogenous bacterial HSPs (Escherichia coli DnaK and Mycobacterium tuberculosis HSP70) delivered an extended OVA peptide for processing and MHC-II presentation, as detected by T hybridoma cells. Bacterial HSPs enhanced MHC-II presentation only if peptide was complexed to the HSP, suggesting that the key HSP function was enhanced delivery or processing of chaperoned peptide Ag rather than generalized enhancement of APC function. HSP-enhanced processing was intact in MyD88 knockout cells, which lack most TLR signaling, further suggesting the effect was not due to TLR-induced induction of accessory molecules. Bacterial HSPs enhanced uptake of peptide, which may contribute to increased MHC-II presentation. In addition, HSPs enhanced binding of peptide to MHC-II molecules at pH 5.0 (the pH of vacuolar compartments), but not at pH 7.4, indicating another mechanism for enhancement of MHC-II Ag processing. Bacterial HSPs are a potential source of microbial peptide Ags during phagocytic processing of bacteria during infection and could potentially be incorporated in vaccines to enhance presentation of peptides to CD4+ T cells.     

Leaf breakdown, detrital resources, and food webs in streams affected by mine drainage

Breakdown of leaf litter is essential for providing detrital resources for food webs but can be impaired by anthropogenic activities, which may disrupt energy flow to consumers. We investigated the relationship between leaf breakdown and food web structure in 12 streams with or without mining impacts on South Island, New Zealand. Six streams received inputs of acid mine drainage (pH 2.5–4.9), three were naturally acidic (pH ~5.0), and three were circumneutral (pH ~6.8). Streams affected by mining either had highly acidic water (pH <3) or iron precipitates present on substrata. Breakdown rates of leaves were significantly lower in mining-affected streams than circumneutral (by almost 50%) but not naturally acidic streams and were driven primarily by microbial activity, as shredding invertebrates were often absent. Mining-affected stream webs were simplified structures with fewer species and links than those in other streams. With few species to process leaf litter and transfer detrital resources, inputs of AMD disrupted both the mechanisms responsible for breakdown and links for energy flow. While faster breakdown rates were associated with larger food webs, limited function maintained in mining-affected streams was sufficient to support primary consumers and small food webs.     

A Computer Simulation Study of Vntr Population Genetics: Constrained Recombination Rules Out the Infinite Alleles Model

Extensive allelic diversity in variable numbers of tandem repeats (VNTRs) has been discovered in the human genome. For population genetic studies of VNTRs, such as forensic applications, it is important to know whether a neutral mutation-drift balance of VNTR polymorphism can be represented by the infinite alleles model. The assumption of the infinite alleles model that each new mutant is unique is very likely to be violated by unequal sister chromatid exchange (USCE), the primary process believed to generate VNTR mutants. We show that increasing both mutation rates and misalignment constraint for intrachromosomal recombination in a computer simulation model reduces simulated VNTR diversity below the expectations of the infinite alleles model. Maximal constraint, represented as slippage of single repeats, reduces simulated VNTR diversity to levels expected from the stepwise mutation model. Although misalignment rule is the more important variable, mutation rate also has an effect. At moderate rates of USCE, simulated VNTR diversity fluctuates around infinite alleles expectation. However, if rates of USCE are high, as for hypervariable VNTRs, simulated VNTR diversity is consistently lower than predicted by the infinite alleles model. This has been observed for many VNTRs and accounted for by technical problems in distinguishing alleles of neighboring size classes. We use sampling theory to confirm the intrinsically poor fit to the infinite alleles model of both simulated VNTR diversity and observed VNTR polymorphisms sampled from two Papua New Guinean populations.     

Interferon-alpha administration enhances CD8+ T cell activation in HIV infection

Background

Type I interferons play important roles in innate immune defense. In HIV infection, type I interferons may delay disease progression by inhibiting viral replication while at the same time accelerating disease progression by contributing to chronic immune activation.

Methods

To investigate the effects of type I interferons in HIV-infection, we obtained cryopreserved peripheral blood mononuclear cell samples from 10 subjects who participated in AIDS Clinical Trials Group Study 5192, a trial investigating the activity of systemic administration of IFNα for twelve weeks to patients with untreated HIV infection. Using flow cytometry, we examined changes in cell cycle status and expression of activation antigens by circulating T cells and their maturation subsets before, during and after IFNα treatment.

Results

The proportion of CD38+HLA-DR+CD8+ T cells increased from a mean of 11.7% at baseline to 24.1% after twelve weeks of interferon treatment (p = 0.006). These frequencies dropped to an average of 20.1% six weeks after the end of treatment. In contrast to CD8+ T cells, the frequencies of activated CD4+ T cells did not change with administration of type I interferon (mean percentage of CD38+DR+ cells = 2.62% at baseline and 2.17% after 12 weeks of interferon therapy). As plasma HIV levels fell with interferon therapy, this was correlated with a “paradoxical” increase in CD8+ T cell activation (p<0.001).

Conclusion

Administration of type I interferon increased expression of the activation markers CD38 and HLA DR on CD8+ T cells but not on CD4+ T cells of HIV+ persons. These observations suggest that type I interferons may contribute to the high levels of CD8+ T cell activation that occur during HIV infection.