Expression of Interferon-gamma and tumour necrosis factor-alpha in pigs experimentally infected with Porcine Reproductive and Respiratory Syndrome Virus (PRRSV).

The expression of mRNA encoding interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) was studied, by reverse transcription-polymerase chain reaction and by in-situ hybridization with a non-radioactive digoxigenin-labelled probe, in formalin-fixed, paraffin wax-embedded lung tissue from pigs experimentally infected with a Korean isolate (North American genotype) of PRRSV. Both IFN-gamma and TNF-alpha mRNA were detected in the lung as early as 1 day post-inoculation (dpi) and up to 10 dpi. Hybridization signals for IFN-gamma and TNF-alpha were usually associated with inflammation, in particular with macrophages within alveolar septa. Expression of these cytokines was minimal in non-lesional lung of PRRSV-infected pigs and in normal lung from control pigs. The results suggest that IFN-gamma and TNF-alpha play a role in pulmonary defence against PRRSV.