| Porcine epidemic diarrhea(PED) caused by the porcine epidemic diarrhea virus(PEDV) is an highly contagious, acute enteric disease characterized by vomiting, watery diarrhea, and dehydration in swine. The outbreak of neonatal piglet diarrhea, resulting in enormous losses of the pig industry in many regions since 2010, is caused by PEDV variant strain and appears more serious clinical symptoms, higher morbidity and mortality than those of previous PED. So far it is insufficiently to understand of the pathogenic and immune characteristics of PEDV and lack of the standard prevention and control program. The objective of this study is to figure out the infection immune characteristics between PEDV and host for laying the foundation of deeply elucidating the pathogenesis of PED.Three-day and twenty one-day old piglets were infected by PEDV HBMC/2012 strains isolated from one pig farm in Hebei province. Pathogenicity of this strain was evalua ted firstly. 3-day old piglets showed tipical symptoms of PED such as severly vomiting and diarrhea on 2 to 3 day post infection(dpi) and the piglets gradually recovered after three days. PEDV nucleic acids were present in rectal swabs from 8 h following infection until to the end of exprement(14 dpi). The thin-walled intestinal full of yellow liquid and gas, falling and incrassate villus were emerge and mesenteric lymph nodes hemorrhaged. And both clinical symptoms and pathological change of 21-day old sick piglets, only various diarrhea without vomiting, were less compared with 3-day old sick piglets. PEDV nucleic acids were detected in serum and intestine on 3 and 7 dpi, but not on 23 dpi. PEDV mainly distributed the middle and distal small intestine and the high detection rate of virus was present in the samll intestinal villlus epithelial cells by the immunohistochemical assay(IHCA). These results showed that PEDV strain HBMC/2012 has obvious pathogenic and the severity of disease caused by this strain is closely related with age.Furthermore, general and local immunity and variation of ralated immune molecules were evaluated via the flew cytometry(FCM), ELISA and IHCA. The levels of spcific antibody reached peak on day 19 after infection with PEDV. The proliferation capacity and the percentage contents of subsets of CD3+CD4+CD8- Th, CD3+CD4-CD8+ Tc, CD3+CD4-CD8-γδT cells and CD3-CD4-CD8+ increased on 3 dpi. CD3-CD4-CD8+ level was obviously lower whereas CD3+CD4-CD8- γδT level still higher than that of the control group, and the same time the contents of CD3+CD4+CD8- Th and CD3+CD4-CD8+ Tc falled on the normal levels on 7 dpi whereas. Immunological memory T cells(CD3+CD4+CD8+) subsets decreased significantly on 3 dpi but increased on 7 dpi. Theses results showed that PEDV could stimuate the production of specific immune responses and various T cell subsets participated in the process of this immune responses.The magnitude of mastocyte, monocyte-macrophages and granulocytes with SWC1 a or/and SWC8 molecules in duodenum, jejunum, ileum, cecum and mesenteric lymph phodes from PEDV-infected piglets was increased. MUC2 secretion of goblet cells significantly decreased while the proliferation activity of mesenteric lymph cells did not change after infection. These results suggested that mastocyte, monocyte-macrophages and some granulocytes paticipated in local immunity induced by PEDV and the decrease of MUC2 levels on the surface of intestinal mucosa probably was the key factor which resulted in piglet diarrhea.The elementary exploration of the pathogenicity and infection immunity characteristics of PEDV strain HBMC/2012 provides valuable information for further study on the pathogenic and immunologic mechanism of this virus. |
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