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

VAN REETH, K.; LABARQUE, G.; NAUWYNCK, H.; PENSAERT, M.

Abstract 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. SIV 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 PI vs 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. PRCV infection was asymptomatic and produced a mild bronchointerstitial pneumonitis and neutrophil infiltration (13 to 22 per cent of BAL cells at 4 d PI ). IFN -α titres parallelled those found during SIV infection, TNF -α was negligible and IL -1 undetectable. PRRSV infection induced anorexia and lethargy between 3 and 5 d PI . There was marked infiltration with mononuclear cells in alveolar septa and BAL fluids between 7 and 10 d PI , while neutrophils remained at less than 11 per cent of BAL cells at any time. IL -1 was produced from three throughout 10 d PI , while IFN -α production was minimal and TNF -α undetectable. These data strongly suggest that proinflammatory cytokines can be important mediators of viral respiratory disease.