(1) and expression of the capsid protein in recombinant baculovirus-infected insect cells (4) have facilitated the study of the virus and the development of a candidate vaccine (5). Expression of the Norwalk virus capsid protein (NVCP) in insect cells yields a protein with an apparent Mr of 58,000 that self-assembles into insect cell-derived Norwalk virus-like particles (i-rNVs) lacking viral RNA, which are reactive with sera from Norwalk virus-infected humans (4). Electron cryomicroscopy of i-rNV shows that the 38-nm empty capsid is composed of 90 dimers of NVCP that form arch-like capsomeres (6). The particles are morphologically and antigenically similar to authentic virus particles, stable on storage at 4°C, stable after lyophilization, and resistant to pH 3.0 treatment (4, 7). These qualities make i-rNV attractive for use as a potential vaccine against Norwalk virus. Recent studies showed that oral immunization of mice with as little as 50 ,ug of i-rNV per dose resulted in the production of serum and mucosal antibodies against NVCP (5). This result is striking in view of the fact that i-rNV is a nonreplicating vaccine and no cholera toxin (CT) adjuvant is needed to achieve immunization.We have experimented with the use of plants as an economical alternative for expression and delivery of recombinant vaccines (8-10). Hepatitis B surface antigen (HBsAg) expressed in tobacco leaves forms subviral particles (8) that are similar to the recombinant yeast-derived antigen, which is licensed for parenteral immunization (11). The plant-derived HBsAg retains both B-and T-cell epitopes when studied in a mouse model (10). Furthermore, the Escherichia coli heatlabile enterotoxin B-subunit expressed in potato tubers and fed to mice without preparation (other than slicing) stimulates serum and gut mucosal antibodies against E. coli labile enterotoxin B-subunit (9). These studies provide proof that recombinant antigens can be produced in transgenic plants, and, at least in some cases, these antigens are orally immunogenic.We report here the expression of recombinant NVCP in transgenic tobacco leaves and potato tubers. The NVCP from tobacco leaves self-assembles into tobacco-derived virus-like particles (t-rNVs) that are morphologically and physically similar to i-rNVs. Further, we show that either partially purified t-rNV given orally or potato tubers expressing NVCP fed directly to mice stimulate the production of antibodies against NVCP. We conclude that a plant-derived edible vaccine for Norwalk virus is feasible. Together with our previous studies, these findings bolster the concept of using transgenic plants for a novel, safe vaccine production and delivery system for developing countries. MATERIALS AND METHODSConstruction of Plant Expression Vectors. A 2.4-kbp DNA fragment containing the gene encoding NVCP was obtained by partial EcoRI digestion of pUCNV4145 (1) and subcloned into pBluescript-KS (Stratagene) at the EcoRI site. One clone (pKSNV2.4) was digested with SmaI and SstI; the resulting 1.9-kbp fragmen...

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Pure MgO, ZrO2 and mixture MgO/ZrO2 nanocrystals were annealed in air from 100 to 1200°C. Variation of the microstructure and defects was investigated by positron lifetime spectroscopy and X-ray diffraction. The experiment results showed that the average positron lifetime of mixture MgO/ZrO2 was more larger than that of single phase MgO and ZrO2, and decreased with the increasing annealing temperature. Thermal annealing below 600°C, the movement of grain boundaries mainly led a reduce of the number of microvoids, and vacancy defects began to recover due to the growth of MgO nanoparticles after annealing between 600 to 900°C. Furthermore, ZrO2 nanoparticles began to grow above 900°C, meanwhile the recovery of vacancy and vacancy clusters in MgO/ZrO2 nanoparticles are restrained because of synergic effect between MgO and ZrO2 nanoparticles.

The oxidized Mo-50Re alloys in air at 573 K and 873 K for various times were investigated by X-Ray diffraction and positron annihilation lifetime spectroscopy. The results indicated that main orthogonal phase MoO3 together with small amount of monoclinic phase Mo8O23 were formed on on the surface of the specimens, and the oxide film of specimens oxidized at 873 K were much thicker than that of specimens oxidized at 573 K. Meanwhile, when Mo-50Re specimens oxidized in air at 873K, the defect’s size within interface layer of the specimens was larger, and the oxide film on the surface of the specimens contained much more defects. Faster oxidation process were observed occured at 873K, which was likely due to the formation of larger-size interfacial defects.