This study revealed that the CSFV-specific IFN-gramma secreting cells, i.e. CSFV-specific cell-mediated immunity, could be detected as early as 6 days post vaccination (dpv) and could be found up to 140 dpv. Pigs immunized once with lapinized Chinese strain CSF vaccine contained a significantly higher number of CSFV-specific IFN-gramma secreting cells (p LT 0.05) than the unvaccinated pigs and were protected from the CSFV challenge in both early (6 dpv) and late challenge (140 dpv) trials. In studying of the efficacy of different types of the CSFV vaccine, groups of pigs, with comparable maternal derived antibody titers, were immunized once with either a lapinized Chinese strain, a tissue culture derived Chinese strain, or GPE strain. The result of this study showed that the GPE vaccine induced CSFV-specific IFN-gramma production, comparable to the group vaccinated with the lapinized Chinese strain and was significant higher than those given the tissue culture derived vaccine and the control group (p LT 0.05). In collaboration with project 1, an ELISPOT assay was used to assess the efficacy of the vaccine programs. Three weeks old pigs, grouped according to the level of maternal derived antibody titer at the time of vaccination as, High (GT=64), Med (16-32) and Low (LT=8), were immunized once when 3 weeks old, or twice at 3 and 5 weeks old. All the vaccinated pigs, regardless of the vaccination protocols, were protected. In collaboration with project 4, an ELISPOT assay was used to study the influence of passive immunity on the induction of anti-CSFV immunity against the CSFV genogroup 2.2. Five weeks old pigs, grouped according to the level of maternal derived antibody at the time of vaccination, as Low (LT=32) and High (64), were immunized once with a lapinized Chinese strain vaccine and challenged 13 dpv with the CSFV genogroup 2.2. Complete protection was evident in the group containing low passive immunity. In contrast, significant inhibition of both cellular and humoral immunity (p LT 0.05) against CSFV were observed in the high passive immunity group, prior to and following the CSFV challenge. Furthermore, CSFV could be isolated from 50 percent of the pigs in this group, at the end of the experiment.