| Summary: | 碩士 === 國立中興大學 === 獸醫學研究所 === 90 === The immune status of the host defense system plays an important role in classical swine fever infection. The experiment was aimed to evaluate the immunomodulator, b-glucan, in the regulation of porcine immune system against CSF virus （S-59 strain） infection. Fifteen 6-week-old, healthy, LYD piglets were grouped as（1）immune-promoting group, pigs fed with the cell wall of Saccharomyces cerevisiae as immune inducer ; （2） immune-inhibiting group, piglets were subsequently injected with dexamethasone ( 1 mg/kg b.w., IM ) to mimic the stress effect on immune system, and （3） control. Virus challenge （S-59, 2 x 106 PFU, IM ) was conducted after 25 days of treatment with S. cerevisiae or dexamethasone . On 0, 7, 14, 21, 28, 42, and 56 days post infection （d.p.i.）, blood samples were collected for WBC count and phenotypic changes in subpopulation of lymphocyte that was analyzed by flow cytometry. Moreover, antigen ELISA and reverse transcriptase-polymerase chain reaction （RT-PCR） were performed to detect the presence of viremia, while the neutralization antibody of experimental pigs after CSF virus challenge was assayed by END method. On 14, 28, and 56 d.p.i., piglets were sacrificed for pathological examination and viral loading and distribution. The results showed that comparing to the control group, the numbers of WBC, lymphocyte, particular in CD4+ lymphocytes in long term treatment of S. cerevisiae was increased. Meanwhile, clinical signs and pathological lesions immune-promoting group were mild and restricted after CSF virus challenge. In contrast, dexamethasone decreased the absolute numbers of CD4+ lymphocytes and aggravated the clinical signs and pathological lesions pigs after CSF virus challenge. These results indicated that proper management along with the application of immunomodulator would enhance host defense and thereby reduce the injury of infectious.
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