SOD activity of cultured peritoneal macrophages 12 h post SPPV immunization. Mice were injected intraperitoneally with PBS, inactivated SPPV, or attenuated SPPV. Peritoneal macrophages were harvested 12 h post inoculation (five/group). Macrophages were co-cultured with LPS1 μg/ml for 48 h, SOD was measured in the culture supernatant. Bars represent mean ± S:E:M: of SOD. SPPV vaccinated mice are significantly different from controls at *P < 0.05.