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. SRV infection was followed within 1 day post inoculation (d PI) by characteristic respiratory and general signs, and excessive lung epithelial desquamation and neutrophil infiltration (38 to 56 per cent of BAL cells at 1 d pr vs 0 to 1 per cent in controls). High concentrations of bioactive interferon-alpha (IFN-alpha), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) coincided with peak symptoms and neutrophil infiltration. PRCV infection was asymptomatic and produced a mild bronchointerstitial pneumonitis and neutrophil infiltration (13 to 22 per cent of BAL. cells at 4 d pr). IFN-alpha titres parallelled those found during sly infection, TNF-alpha was negligible and Ir-l undetectable. PRRSV infection induced anorexia and lethargy between 3 and 5 d pr. There was marked infiltration with mononuclear cells in alveolar septa and Bps fluids between 7 and 10 d pr, while neutrophils remained at less than ii per cent of BAL cells at any time. IL-1 was produced from three throughout 10 d pr, while IFN-alpha production was minimal and TNF-alpha undetectable. These data strongly suggest that proinflammatory cytokines can be important mediators of viral respiratory disease.