| Porcine edema disease (ED) is mainly caused by some definite serotype shiga-like toxin(SLT) Escherichia coli which lead to edema of the head and the stomach submucosa, ataxia, spasm and tetraplegia. ED is an acute disease. Because the onset of disease is often sudden and the course rapid and mortality rate is very high. Edema disease is transmitted via the alimentary infection. According to the feature of mucosa infection, effective oral vaccine which can induce local and systematic immunity is of great significance for the prevention and control.In this study, E. coli O139 * microcapsules were prepared by pressurization, and the diameter of microcapsules was 2mm, the encapsulation rate was 76%. They could tolerate the pH1.6 artificial gastric acid for 3 hours and could be released in pH6.8 artificial intestinal juice. The microcapsules was safe for piglets, the appetite , the water-drinking, the weight gain and the mental state were normal, there was no any adverse reaction.Nine 35-day-old piglets were divided randomly into 3 groups of 3 piglets which were immunized via oral with O139* mutant strains microcapsules, O139* mutant strains liquid, PBS, respectively, one time every day for 3 days. The specific IgG in piglet serum and sIgA in faeces were detected by indirect ELISA. The results showed that the IgG anti-O139, anti-F18ab were found after immunization 21d and 28d(P/N>2), the IgG anti-SLT-ⅡeA wes found after immunization 7d(P/N>2), the IgG anti-SLT-ⅡeB was not found in microcapsules group. The sIgA anti-SLT-ⅡeA appeared after immunization 7d, 21d and 28d in their feces(P/N>2), the sIgA anti-O139 appeared after immunization 14d and 21d(P/N>2), the the sIgA anti-SLT-ⅡeB appeared after immunization 7d(P/N>2)also in microcapsules group. The specific IgG in serum and specific sIgA in faeces also were found in mutant strains liquid group, but the level were lower than those of microcapsules group. The specific IgG and specific sIgA were not found in PBS control group.The content of IL-4, IL-10, IFN-γin serum were detected by ELISA kit. The results showed that the content of IL-10 had risen significantly from 219.95 pg/mL to 354.65 pg/mL, the IL-4 had risen from 58.146 pg/mL to 75.762 pg/mL, the IFN-γhad no significantly change. The SLT-Ⅱe gene mutant strain of Escherichia coli were detected from faecse after immunization 21d in microcapsules group and mutant strains liquid group.After the last immunization 28d, one piglet was chosed randomly from microcapsules group and PBS control group, respectively, then they were injected via ear vein with 18ml of SLT-Ⅱe. The results showed that the piglet from microcapsules group didn't like move, appeared dcreased appetite, then resumed normal after 24 hours. The another one from control group appeared appetite waste away, fever, lateral decubitus. The piglets were killed after injection 72 hours, the visible pathological changes were not found in main tissues and organs of piglet from microcapsules group. The piglet from PBS control group appeared focal necrosis on liver edge, pneumonia, edema in gastric mucosa and gallbladder; The histological pathological changes showed that the gastric submucosal edema, liver cell degeneration and necrosis, the hemal wall permeability increase in lung, kidney , spleen, and erythrocytes exudates.The results of this study demonstrated that the microcapsules can protected the O139* mutant strains to resist the artificial gastric acid, and released the mutant strains well in ntestinal which colonized in there, then the mutant strains induced humoral immune and mucosa immune, provided effective protection for immunized piglets. So, the mutant strain of E coli can be used as a candidate of oral virulence gene deletion vaccine to against the edema disease of swine. |
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