The effect of porcine circovirus type 2 (PCV2) on the classical swine fever virus (CSFV)-specific cell proliferation reponse of peripheral blood mononuclear cells (PBMCs) in various ex vivo treatments. The PBMCs were collected from pigs that had been vaccinated with Lapinized Philippines Coronel (LPC) vaccine twice, followed by challenge with wild-type CSFV (ALD) 6 weeks later. The PBMCs were pre-inoculated with 0.1, 0.05 or 0.01 MOI of PCV2, 0.1 MOI of UV-inactivated PCV2 or Con A at 5 μg/mL followed by inoculation with 1 MOI of wild-type CSFV 18 h later. This ex vivo CSFV-specific cell proliferation response was done in triplicates and assayed 4 days after wild-type CSFV stimulation by commercial kits as indicated in the material and methods. The values are shown as mean ± SD of five different pigs. a-dValues with different superscripts indicate that the differences among groups are statistically significant (P < 0.05).