Inducible nitric oxide synthase expression in porcine immune cells

Porcine immune cells were examined for the ability to produce inducible nitric oxide synthase following in vitro or in vivo stimulation. Enzyme activity and product formation were not detected following stimulation of porcine peripheral blood mononuclear cells (PBMC), splenocytes, or alveolar macrophages with a combination of ConA and lipopolysaccharide (LPS) or recombinant porcine interferon γ and LPS. In vitro engulfment of Haemophilus parasuis by macrophages also failed to induce inducible nitric oxide synthase (iNOS) activity or nitrite formation. Swine Herpes Virus infection led to a small but significant increase in level of nitrite detected in lung lavage fluid, whereas the infection of pigs with Porcine Respiratory and Reproductive Syndrome Virus did not alter the lavage fluid nitrite levels. iNOS mRNA was detected in both stimulated and unstimulated porcine immune cells and in macrophages from both control and infected animals suggesting that it is constitutively expressed with little or no upregulation following cellular stimulation. The results presented in this paper indicate that the reactive nitrogen intermediate pathway is not an vital innate immune response in the pig.