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

Abstract

Tumour necrosis factor-alpha (TNF-alpha) has been shown to play a role in many inflammatory conditions. Currently anti-TNF-alpha drugs (e.g. etanercept) are used in humans for treatment of autoimmune diseases. In this study we aimed to elucidate the role of TNF-alpha 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 0.5mg/per route/per pig. High anti-TNF-alpha activity was detected in bronchoalveolar lavage (BAL) fluids, peritoneal lavage fluids and serum of all animals for at least 8h post-inoculation (HPI). No clinical symptoms, lung lesions, lung cell infiltration or induction of IFN-alpha, IL-1, IL-6, IL-12 and TNF-alpha in BAL were detected. Subsequently, the ability of etanercept to block porcine TNF-alpha 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) 24h 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 8h after LPS inoculation. TNF-alpha 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-alpha, IL-1, IL-6 and IL-12/IL-23 were observed between the two groups. Blocking of TNF-alpha 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.

Fig. 1

TNF-α levels in bronchoalveolar lavage fluids of PRCV-LPS (open circles) and PRCV-LPS-Enbrel (filled circles) inoculated pigs. Mean TNF-α titres are shown by dashes. The dotted line represents the detection limit of the assay (40 U/ml).

Fig. 2

Comparison of the evolution of clinical symptoms between PRCV-LPS and PRCV-LPS-Enbrel inoculated pigs. Half of the animals in each group were euthanized at 4 h after monitoring.

Fig. 3

Comparison of IL-1, IL-6, IL-12/IL-23 and IFN-α levels in bronchoalveolar lavage fluids of PRCV-LPS (open circles) and PRCV-LPS-Enbrel (filled circles) inoculated pigs. Average values are shown by dashes. The dotted line represents the detection limit of each assay (40 U/ml for IFN-α, IL-1 and IL-6, and 18 pg/ml for IL-12/23).

Fig. 4

Haematoxylin–eosin staining of the lungs of pigs inoculated with PBS-only (A) (100×), Enbrel-only (B) (100×), PRCV-LPS (C) (100×) and (D) (200×), and PRCV-LPS-Enbrel (E) (100×) and (F) (200×).