Increased pulmonary secretion of tumor necrosis factor-alpha in calves experimentally infected with bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) is an important cause of respirat ory disease among calves in the Danish cattle industry. An experimental BRS V infection model was used to study the pathogenesis of the disease in calv es. Broncho alveolar lung lavage (BAL) was performed on 28 Jersey calves, o f which 23 were experimentally infected with BRSV and five were given a moc k inoculum. The presence of the cytokine tumor necrosis factor alpha (TNF-a lpha) in the BAL fluids was detected and quantified by a capture ELISA. TNF -alpha was detected in 21 of the infected animals. The amount of TNF-alpha in the BAL fluid of calves killed post inoculation day (PID) 2 and 4 was at the same very low level as in the uninfected control animals. Large amount s of TNF-alpha were detected on PID 6, maximum levels of TNF-alpha were rea ched on PID 7, and smaller amounts of TNF-alpha were seen on PID 8. The hig h levels of TNF-alpha appeared on the days where severe lung lesions and cl inical signs were obvious and the amounts of BRSV-antigen were at their gre atest. Although Pasteurellaceae were isolated from some of the BRSV-infecte d calves, calves treated with antibiotics before and through the whole peri od of the infection, as well as BRSV-infected calves free of bacteria reach ed the same level of TNF-alpha as animals from which bacteria were isolated from the lungs. It is concluded that significant quantities of TNF-alpha a re produced in the lungs of the calves on PID 6-7 of BRSV infection. The in volvement of TNF-alpha in the pathogenesis of, as well as the anti-viral im mune response against, BRSV infection is discussed. (C) 2000 Elsevier Scien ce B.V. All rights reserved.