TNF and infection: For the Pietrain pigs a negative correlation between the TNF-α production by blood leukocytes in vitro and clinical scores was found at pre-infection as well as at 4 and 21 days post-infection (r = -0.45; p < 0.05 at day -7; r = -0.48; p < 0.05 at day 4 and r = -0.61; p < 0.05 at day 21).