Platelet-activating factor (PAF) has been implicated as a mediator of inflammation, allergy, shock, and thrombosis. A specific degradative enzyme, PAF acetyihydrolase (EC 3.1.1.47), is found in plasma and could regulate the concentration of PAF in blood. In plasma, 70% of the PAF acetylhydrolase is found with low density lipoprotein (LDL), and the remainder is in high density lipoprotein (HDL). In previous studies we found that with subsaturating concentrations of PAF the activity in LDL seemed to be the relevant one; e.g., depletion of LDL slowed degradation of PAF, while removal of HDL accelerated the degradation slightly. We have pursued this observation by using plasma from humans with lipoprotein mutations. In abetalipoproteinemia, all of the PAF acetylhydrolase activity was in HDL, whereas in Tangier disease all of the activity was in LDL. In both conditions the total activity measured in an optimized assay was normal or increased. However, when we measured the t1/2 of PAF in plasma, we found that it was prolonged in subjects with abetalipoproteinemia compared to normal controls. Conversely, the t1/2 in Tangier plasma was shortened. We next demonstrated that the PAF acetylhydrolase in HDL was recognized by an antibody to the enzyme purified from LDL, establishing that the enzyme in the two particles is the same protein. Finally, we inactivated the PAF acetylhydrolase in isolated lipoprotein particles and then reconstituted them with enzyme from the opposite particle. The reconstituted particles were used to measure the t1/2 of PAF, and we again found that the LDL particle was more efficient. We conclude that the lipoprotein environment of the PAF acetylhydrolase markedly influences its catalytic behavior. This may be important in pathophysiology and will complicate attempts to assess the role of this enzyme in such circumstances.
SUMMARY During the recent Ebola crisis in West Africa, individual person-level details of disease onset, transmissions, and outcomes such as survival or death were reported in online news media. We set out to document disease transmission chains for Ebola, with the goal of generating a timely account that could be used for surveillance, mathematical modeling, and public health decision-making. By accessing public web pages only, such as locally produced newspapers and blogs, we created a transmission chain involving two Ebola clusters in West Africa that compared favorably with other published transmission chains, and derived parameters for a mathematical model of Ebola disease transmission that were not statistically different from those derived from published sources. We present a protocol for responsibly gleaning epidemiological facts, transmission model parameters, and useful details from affected communities using mostly indigenously produced sources. After comparing our transmission parameters to published parameters, we discuss additional benefits of our method, such as gaining practical information about the affected community, its infrastructure, politics, and culture. We also briefly compare our method to similar efforts that used mostly non-indigenous online sources to generate epidemiological information.
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