Trap-assisted enhancement of the responsivity in asymmetric planar GaN-based nanodiodes at low temperature.

The microwave detection capability of GaN-based asymmetric planar nanodiodes (so-called Self-Switching Diode, SSD, due to its non-linearity) has been characterized in a wide temperature range, from 70 K up to 300 K. At low temperature, microwave measurements reveal an enhancement of the responsivity at frequencies below 1 GHz, which, together with a pronounced hysteresis in the DC curves, indicate a significant influence of the surface states. This leads to a significant variability and non-repeatability which needs to be reduced since it degrades the accuracy of the detection. For this sake, the RF characterization was repeated after applying a positive/negative voltage able to fill/empty the surface states in order to have a well-established preconditioned state. As a consequence of the positive pre-soak bias, a significant enhancement of the measured responsivity, with a × 10 increase at low temperature. The RF detection measurements after such preconditioning contains a time dependence induced by the slow discharge mechanism of the traps, so that the improved responsivity remains even after 100s of seconds. On the other hand, a negative voltage pre-soak benefits the discharge process, thus suppressing the low frequency dispersion and the important variability of the detection without the pre-conditioning step. We also show that the relation between the voltage and current responsivities in each case allows to explain the impact of the surface charges in terms of the device impedance.

Trap-related frequency dispersion of zero-bias microwave responsivity at low temperature in GaN-based self-switching diodes.

The zero-bias microwave detection capability of self-switching diodes (SSDs) based on AlGaN/GaN is analyzed in a wide temperature range, from 10 K to 300 K. The measured responsivity shows an anomalous enhancement at low temperature, while the detected voltage exhibits a roll-off in frequency, which can be attributed to the presence of surface and bulk traps. To gain a deep insight into this behavior, a systematic DC and AC characterization of the diodes has been carried out in the mentioned temperature range. DC results confirm the existence of traps and AC measurements allow us to identify their properties. In particular, impedance studies enable to distinguish two types of traps: at the lateral surfaces of the channel, with a wide spread of relaxation times, and in the bulk.

Enhancing DNA immunization by targeting ASFV antigens to SLA-II bearing cells.

One of the main criticisms to DNA vaccines is the poor immunogenicity that they confer on occasions, at least in large animals. Confirming this theory, immunization with plasmid DNA encoding two African swine fever virus genes in frame (pCMV-PQ), failed in inducing detectable immune responses in pigs, while it was successful in mice. Aiming to improve the immune responses induced in swine, a new plasmid was constructed, encoding the viral genes fused in frame with a single chain variable fragment of an antibody specific for a swine leukocyte antigen II (pCMV-APCH1PQ). Our results clearly demonstrate that targeting antigens to antigen professional cells exponentially enhanced the immune response induced in pigs, albeit that the DNA vaccine was not able to confer protection against lethal viral challenge. Indeed, a viremia exacerbation was observed in each of the pigs that received the pCMV-APCH1PQ plasmid, this correlating with the presence of non-neutralizing antibodies and antigen-specific SLA II-restricted T-cells. The implications of our discoveries for the development of future vaccines against African swine fever virus and other swine pathogens are discussed.

Interferon-gamma induction correlates with protection by DNA vaccine expressing E2 glycoprotein against classical swine fever virus infection in domestic pigs.

Classical swine fever (CSF) is a highly contagious viral infection affecting domestic and wild pigs. For classical swine fever virus (CSFV), immunization with plasmids expressing different versions of glycoprotein E2 has proven an effective way to induce protection. Previously, we have also shown that immunization with DNA vaccine expressing glycoprotein E2 (DNA-E2) induced specific T helper cell responses in the absence of neutralizing antibodies. However, the role of T cell responses in protection against CSFV is largely unknown. Here we have extended these studies to deeply characterize the role of T cell responses by a DNA-E2 and their correlation with protection against CSFV infection. Thus, pigs vaccinated with the DNA vaccine induced a strong cellular immune response, characterized by the specific induction IFN-gamma expressing T cells after vaccination without any detectable levels of CSFV neutralizing antibodies. Constant levels of CSFV-specific IFN-gamma producing cells observed from the beginning of the infection until 7 days after challenge in vaccinated animals might contribute to early control of CSFV replication, at least until neutralizing antibodies are developed. Severe clinical signs of the disease, including high titers of viremia, pyrexia and virus spread to different organs, were recorded in the non-vaccinated challenged animals, in comparison to the vaccinated animals where only one animal showed mild clinical signs and a short peak of viremia. Lack of complete protection in this animal correlated with a delay on the induction of neutralizing antibodies, detectable only from day 11 post-CSFV challenge. Conversely, the rest of the pigs within the group developed neutralizing antibodies as early as at day two post-challenge, correlating with sterile protection. Finally, an inverse correlation seemed to exist between early induction of IFN-alpha and the protection observed, while IL-10 seemed to be differentially regulated in vaccinated and non-vaccinated animals. Our results support the relevance of the induction of a strong T cellular response to confer a solid protection upon DNA vaccination against CSFV. Further experiments are needed to be done in order to clarify the key cytokines playing a role in CSFV-protection and to obtain emergency vaccines capable to confer robust and fast protection.

One dose of a porcine circovirus 2 (PCV2) sub-unit vaccine administered to 3-week-old conventional piglets elicits cell-mediated immunity and significantly reduces PCV2 viremia in an experimental model.

The immunogenicity and efficacy generated by one dose of a PCV2 sub-unit vaccine (Porcilis PCV) were evaluated in 3-week-old conventional piglets. Vaccination induced both humoral and cell-mediated responses against PCV2, which were increased after the challenge with a PCV2 genotype "b" isolate. High levels of maternally derived antibodies (IPMA >or= 10 log(2)) at the time of vaccination were found to interfere with the active seroconversion, whereas titres below 8 log(2) allowed the development of a proper antibody response. Nevertheless, the immunity induced by one dose of the product was partly protective against PCV2 infection, since viremia, shedding and viral load in tissues were significantly reduced in vaccinated pigs compared to controls.

Evidence of potential gene flow in Trichinella spiralis and in Trichinella britovi in nature.

During a study on the epidemiology of trichinellosis in Spain, 91 animals and 9 samples of sausages homemade with pork were found positive for Trichinella. Parasite identification at the species level was carried out by the polymerase chain reaction with a random primer on single muscle larvae. Seventy-one animals harbored Trichinella spiralis (17 domestic pigs, 53 wild boars, 1 fox), and 17 were infected with Trichinella britovi (1 domestic pig, 13 wild boars, 3 foxes). Sausages were infected with T. spiralis. Three wild boars (3.3% of infected animals) harbored both species. The presence of both T. spiralis and T. britovi in the same host suggests that infections with 2 isolates of the same species can also occur, permitting the gene flow within the species.