Differential production of proinflammatory cytokines in the pig lung during different respiratory virus infections: correlations with pathogenicity

The acute stages of infection with swine influenza virus (SIV), porcine respiratory coronavirus (PRCV) and porcine reproductive-respiratory syndrome virus (PRRSV) were shown to differ in terms of clinical and lung inflammatory effects and proinflammatory cytokine profiles in bronchoalveolar lavage (BAL) fluids. Caesarian-derived colostrum-deprived pigs were inoculated intratracheally with one of the three viruses.SIVinfection was followed within 1 day post inoculation (dPI) by characteristic respiratory and general signs, and excessive lung epithelial desquamation and neutrophil infiltration (38 to 56 per cent ofBALcells at 1 dPIvs 0 to 1 per cent in controls). High concentrations of bioactive interferon-α (IFN-α), tumour necrosis factor-α (TNF-α) and interleukin-1 (IL-1) coincided with peak symptoms and neutrophil infiltration.PRCVinfection was asymptomatic and produced a mild bronchointerstitial pneumonitis and neutrophil infiltration (13 to 22 per cent ofBALcells at 4 dPI).IFN-α titres parallelled those found duringSIVinfection,TNF-α was negligible andIL-1 undetectable.PRRSVinfection induced anorexia and lethargy between 3 and 5 dPI. There was marked infiltration with mononuclear cells in alveolar septa andBALfluids between 7 and 10 dPI, while neutrophils remained at less than 11 per cent ofBALcells at any time.IL-1 was produced from three throughout 10 dPI, whileIFN-α production was minimal andTNF-α undetectable. These data strongly suggest that proinflammatory cytokines can be important mediators of viral respiratory disease.