Expression of nitric oxide synthase 2 and cyclooxygenase-2 in swine experimentally infected with Actinobacillus pleuropneumoniae

The expression of inflammatory mediators was examined in pigs experimentally infected with Actinobacillus pleuropneumoniae. The activity of nitric oxide synthase 2 (NOS2) and cyclooxygenase-2 (COX-2) was determined by measuring nitric oxide (NO) and prostaglandin E2 (PGE2) in bronchoalveolar lavage fluid in response to A. pleuropneumoniae in vivo. By in situ hybridization and immunohistochemistry, both NOS2 and COX-2 enzymes were detected in neutrophils and macrophages that had infiltrated into alveolar spaces. The sharp increase in PGE2 concentration preceded the increase in the concentrations of NO. NO levels were highly correlated with PGE2 level (rs=0.7218, P <0.05). The NO levels were positively correlated with lung lesion scores (rs=0.9087, P <0.05) until 24 hours postinoculation (hpi) as were the lung lesion scores and PGE2 levels (rs=0.925, P <0.01). High levels of PGE2 produced by COX-2 are generated in early infection (6 hpi). However, in later stages of infection (12-36 hpi), there is participation of NO and PGE2 accompanied by coinduction of both NOS2 and COX-2.