| Summary: | 碩士 === 國立臺灣大學 === 分子暨比較病理生物學研究所 === 107 === The newly emerging variant of group 2b (G2b) porcine epidemic diarrhea virus (PEDV) leading to porcine epidemic diarrhea (PED) with characteristic of acute severe diarrhea and vomiting, dehydration or even death has devastated the swine industry in Taiwan since late 2013. After 2015, the novel G2b PEDV variant further transformed into a cyclical outbreak. To understand the diversity of PEDVs circulating in Taiwan after 2016, phylogenetic analysis of genetic sequence of the S gene of PEDVs collected during 2016-2018 in Taiwan were compared with the historic and global PEDV strains (Chapter II). The next generation sequencing (NGS) was further performed for the analysis of a potential recombinant Taiwan PEDV variant. In addition, the successful induction of mucosal immunity has always been a bottleneck for the development of vaccines by route of intramuscular (IM) administration. In Chapter III, three porcine CCL proteins (CCL27, CCL28, and CCL25) derived from mammalian cell expression system were constructed and applied as mucosal immune adjuvants with an inactivated PEDV (iPEDV) as immunogen by IM immunization. The immunogenicity and protective efficiency of the iPEDV adjuvanted with different combinations of CC chemokines (CCL27, CCL28 and/or CCL25) were evaluated in 5-week-old pigs by IM immunization to develop the novel vaccine strategy for inducing mucosal immune responses.
In Chapter II, a total of 31 intestinal and/or fecal specimens from 1-day to 6-week old piglets or sows with watery diarrhea confirmed to be PEDV-positive by quantitative reverse transcription polymerase chain reaction (RT-qPCR) from 28 different herds in Taiwan during 2016-2018 were sequenced and analyzed. The phylogenetic analysis of the S gene of PEDV revealed that the majority (28/31) of Taiwan new PEDV strains, except for the TW/Yunlin550/2018 strain, were closely related to the global G2b PEDV strains with unique deletions and insertions scattered in the neutralizing epitope regions of the S protein as compared to the historic G2b PEDV strains. Moreover, the TW/Yunlin550/2018 strain was proposed a recombinant between a G2b strain and a circulating wild-type PEDV G1 strain based on the results of sequencing of S gene and NGS of the whole PEDV genome.
In Chapter III, three porcine CCL proteins (CCL27, CCL28, and CCL25) derived from the mammalian cell expression system were stably expressed and applied as vaccine adjuvants. In the experiment of post-weaning pigs, our data showed that IM co-administration of iPEDV with the above mentioned chemokines as adjuvants for two times at a two-week interval could induce higher levels of systemic PEDV-specific immunoglobulin (Ig) G, mucosal PEDV-specific IgA, and viral neutralizing antibody titer; and better substantial protection against PEDV challenge than those administrated without CC chemokines and in control pigs. The present study verified that IM immunization with different combinations of porcine CC chemokines could trigger their unique immune trafficking abilities to elevate the antigen-specific systemic and mucosal immune responses simultaneously. These porcine CC chemokines can be used in the vaccine development for not only PEDV but also other mucosal transmissible swine diseases.
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