Anti-TNF-α therapy does not ameliorate disease in a model of acute virus-endotoxin mediated respiratory disease in pigs

Tumour necrosis factor-α (TNF-α) has been shown to play a role in many inflammatory conditions. Currently anti-TNF-α drugs (e.g. etanercept) are used in humans for treatment of autoimmune diseases. In this study we aimed to elucidate the role of TNF-α in the development of virus-endotoxin-induced respiratory disease. Twenty-two caesarean derived colostrum deprived pigs were used. Initially, the availability in the lungs and circulation, and possible clinical and inflammatory effects of etanercept alone were assessed in 4 pigs after intratracheal and intraperitoneal administration of 0.5 mg/per route/per pig. High anti-TNF-α activity was detected in bronchoalveolar lavage (BAL) fluids, peritoneal lavage fluids and serum of all animals for at least 8 h post-inoculation (HPI). No clinical symptoms, lung lesions, lung cell infiltration or induction of IFN-α, IL-1, IL-6, IL-12 and TNF-α in BAL were detected. Subsequently, the ability of etanercept to block porcine TNF-α and its effect on the above mentioned parameters and on lung virus titres were assessed in 8 pigs. They were inoculated intratracheally with porcine respiratory coronavirus (PRCV) followed by lipopolysaccharide (LPS) 24 h later. Etanercept was administered at the time of LPS inoculation via the same routes and dose as in the initial experiment. The parameters were compared with a control group (n = 8), receiving only PRCV-LPS. Half of the animals from each group were euthanized at 4 and the rest at 8 h after LPS inoculation. TNF-α was completely neutralized in 3 of the 4 animals euthanized at 4 HPI and significantly lower than in the PRCV-LPS group at all times. No significant differences in disease severity, lung lesions, virus replication, lung cell infiltration or levels of IFN-α, IL-1, IL-6 and IL-12/IL-23 were observed between the two groups. Blocking of TNF-α alone was not sufficient to ameliorate disease in the PRCV-LPS model of respiratory disease, possibly due to the redundancy in the proinflammatory cytokine cascade, or the involvement of other unidentified disease mediators.