Ventilator-induced lung injury plays a crucial role in the outcome of patients with
acute lung injury. Previous studies have shown a role for the
cytokine tumor necrosis factor-alpha (TNF) in stretch-induced alveolar neutrophil recruitment, but the involvement of TNF in stretch-induced
pulmonary edema is unclear. We investigated the effects of TNF through its individual p55 and p75 receptors on early
pulmonary edema formation during high stretch ventilation, before neutrophil infiltration. Anesthetized wild-type or
TNF receptor single/double knockout mice were ventilated with high tidal volume ( approximately 38 ml/kg) for 2 h or until they developed arterial
hypotension.
Pulmonary edema was assessed by physiological parameters including respiratory mechanics and blood
gases, and by lavage fluid
protein,
lung wet:dry weight ratio, and lung permeability measurements using fluorescence-labeled
albumin. High stretch ventilation in wild-type and
TNF receptor double knockout animals induced similar
pulmonary edema, and only 25-30% of mice completed the protocol. In contrast, the p55 receptor knockout mice were strongly protected from
edema formation, with all animals completing the protocol.
Myeloperoxidase assay indicated that this protective effect was not associated with decreased pulmonary neutrophil sequestration. The p75 receptor knockout mice, however, displayed increased susceptibility to
edema formation, and no animals survived the full 2 h. These results demonstrate a novel role for TNF signaling (independent from its effects on neutrophil recruitment) specifically through the p55 receptor, in promoting high stretch-induced
pulmonary edema, whereas p75 signaling may play an opposing role.