Introduction and Objectives Tumour necrosis factor (TNF) alpha is transiently up-regulated within the alveolar space during ventilator-induced lung injury (VILI). We previously found that the two TNF receptors play opposing roles during VILI in knock-out mice, with p55 promoting but p75 preventing pulmonary oedema. This suggests that specific blockade of p55 receptor signalling within the alveolar space may be beneficial in VILI. Domain antibodies (dAbs) are the smallest antigen-binding fragments of the IgG molecule, which may have advantages over complete antibodies due to their small size and monovalent binding (mAbs often have agonist activity due to receptor cross-linking). In this study we tested the effects of an intratracheally (i.t.) delivered dAb that binds to and inhibits the murine p55 receptor (Biopharmaceutical R&D, GlaxoSmithKline), on pulmonary oedema and inflammation in mouse models of VILI.

Methods C57BL6 mice were ventilated with a high-stretch protocol (standardised by plateau pressure at 12.5–13.5 cm H₂O; tidal volume 20–22 ml/kg, PEEP 3 cm H₂O, O₂ with 2–4% CO₂). Mice then received an i.t. bolus of either non-specific ‘dummy’ dAb or p55-specific dAb (25 μg in 50 μl), and were ventilated for up to 4 h (1-hit model). As a 2-hit model, 20 ng LPS were included in the dAb bolus. Development of lung injury was assessed by respiratory elastance and blood gases, and protein level in bronchoalveolar lavage fluid (BALF) at termination. In the 2-hit model, neutrophil infiltration into BALF, the activation state of alveolar macrophages, and neutrophil margination within lung vasculature were all assessed by flow cytometry.

Results High stretch ventilation produced deteriorations in elastance and PO₂ and high BALF protein in both models. Treatment with the p55-specific dAb substantially attenuated all of these changes in the 1-hit model (Abstract T2 Table 1). In the 2-hit model, p55 blockade prevented deteriorations in elastance and oxygenation, and significantly decreased neutrophil margination, intraalveolar neutrophil infiltration and ICAM-1 expression on alveolar macrophages.

Conclusions Use of dAbs to selectively inhibit intra-alveolar p55 TNF receptor signalling may open new therapeutic approaches for ventilated patients with acute lung injury. This study was supported by Biopharmaceutical R&D, GlaxoSmithKline.