TNF and infection: Blood and bronchoalveolar lavage fluid (BALF) leukocytes were harvested from four different pig breeds at 7 days pre-infection and 4 and 21 days post-infection and their activation was studied by measuring the production of H2O2, NO and TNF-α after stimulation with A. pleuropneumoniae, S. suis, lipopolysaccharide (LPS) and phorbol miristate acetate (PMA).