Plasmacytoid Dendritic Cells Sequester High Prion Titres at Early Stages of Prion Infection

In most transmissible spongiform encephalopathies prions accumulate in the lymphoreticular system (LRS) long before they are detectable in the central nervous system. While a considerable body of evidence showed that B lymphocytes and follicular dendritic cells play a major role in prion colonization of lymphoid organs, the contribution of various other cell types, including antigen-presenting cells, to the accumulation and the spread of prions in the LRS are not well understood. A comprehensive study to compare prion titers of candidate cell types has not been performed to date, mainly due to limitations in the scope of animal bioassays where prohibitively large numbers of mice would be required to obtain sufficiently accurate data. By taking advantage of quantitative in vitro prion determination and magnetic-activated cell sorting, we studied the kinetics of prion accumulation in various splenic cell types at early stages of prion infection. Robust estimates for infectious titers were obtained by statistical modelling using a generalized linear model. Whilst prions were detectable in B and T lymphocytes and in antigen-presenting cells like dendritic cells and macrophages, highest infectious titers were determined in two cell types that have previously not been associated with prion pathogenesis, plasmacytoid dendritic (pDC) and natural killer (NK) cells. At 30 days after infection, NK cells were more than twice, and pDCs about seven-fold, as infectious as lymphocytes respectively. This result was unexpected since, in accordance to previous reports prion protein, an obligate requirement for prion replication, was undetectable in pDCs. This underscores the importance of prion sequestration and dissemination by antigen-presenting cells which are among the first cells of the immune system to encounter pathogens. We furthermore report the first evidence for a release of prions from lymphocytes and DCs of scrapie-infected mice ex vivo, a process that is associated with a release of exosome-like membrane vesicles

Estimation of pesticide mixture interaction in Nile tilapia (Oreochromis niloticus) using survival analysis

The acute toxicity of the pesticides atrazine, mancozeb, chlorpyrifos and lambda-cyhalothrin, acting singly and jointly, was assessed on Nile tilapia (Oreochromis niloticus) fingerlings. Median lethal concentration (LC50), median lethal time (LT50), and mixture interaction were estimated, whereas survival analysis was used to model time-todeath. The most toxic single and joint mixture was lambda-cyhalothrin and chlorpyrifos-lambda cyhalothrin, respectively. The risk of death (RoD) of fingerlings exposed to 9.22 mg l−1 atrazine-mancozeb mixture was 1.76 times higher than fingerlings exposed to 9.0 mg l−1 atrazine (p > 0.05). However, RoD of fingerlings exposed to 9.95 mg l−1 atrazine-chlorpyrifos was 5.59 times higher than fingerlings exposed to 9.0 mg l−1 atrazine (p < 0.01). The risk of death of fingerlings exposed to 20.8 mg l−1 atrazine-lambda cyhalothrin was 2.81 times higher than 21.0 mg l−1 atrazine. The toxicity of 2.3 mg l−1 mancozeb-chlorpyrifos was 254.25 higher than 2.2 mg l−1 mancozeb (p < 0.01). Fingerlings exposed to 4.33 mg l−1 mancozeb-lambda cyhalothrin and 0.177 mg l−1 chlorpyrifos-lambda cyhalothrin mixture were 0.02 and 0.14 times less likely to die than those exposed to 4.8 mg l−1 mancozeb and 0.17 mg l−1 chlorpyrifos, respectively (p < 0.01). Atrazine-mancozeb, atrazine-chlorpyrifos, atrazine-lambda cyhalothrin, and mancozeb-chlorpyrifos interaction were synergistic, and their relative risk was >1. Both mancozeb-lambda cyhalothrin and lambda-cyhalothrin-chlorpyrifos mixtures were antagonistic, and their relative risk was less than 1. Survival analysis can show interaction in complex pesticide mixtures