Pulmonary Edema Fluid from Patients with Early Lung Injury Stimulates Fibroblast Proliferation through IL-1β-Induced IL-6 Expression

Abstract

Although the fibroproliferative response to lung injury occurs with a high frequency in patients with clinical acute lung injury, the mechanisms that initiate this response are largely unknown. This study was undertaken first to identify fibroblast mitogenic factors in pulmonary edema fluid, and second to examine the human lung fibroblast’s gene expression profile in response to pulmonary edema fluid. The edema fluid obtained from patients with early lung injury has an eightfold higher concentration of IL-1β and a twofold greater IL-1β-dependent mitogenic effect than does fluid obtained from control patients with hydrostatic pulmonary edema. Furthermore, fibroblasts responded to acute lung injury patient-derived edema fluid through production of soluble mediators that possess an autocrine mitogenic effect. Gene array analysis reveals that acute lung injury edema fluid induces several inflammation-modulating and proliferation-related genes in fibroblasts, whose inductions are similarly dependent on bioactive IL-1β. Most notably, the 20-fold induction of IL-6 mRNA and protein was completely blocked by IL-1 receptor antagonist. The combined addition of IL-1β and IL-6 was mitogenic, and the proliferative response to conditioned medium from IL-1β-exposed cells was blocked by antagonistically acting Abs to IL-6 or to gp130. These novel findings indicate that soluble IL-1β bioactivity and autocrine IL-1β-dependent IL-6 up-regulation are critical initiators of fibroblast activation and proliferation and that they likely play a role in the fibroproliferative response seen in human acute lung injury.

Prostaglandin E2 Mediates IL-1β-Related Fibroblast Mitogenic Effects in Acute Lung Injury through Differential Utilization of Prostanoid Receptors

“…Patients were eligible for inclusion in this study if they had acute pulmonary edema from either ALI or hydrostatic causes and required endotracheal intubation for positive pressure ventilation. Pulmonary edema fluid was obtained from patients within 4 h of intubation through gentle luminal suction applied to a 14 French catheter passed into the distal airways, as described previously (22,38). Samples were centrifuged (3000 ϫ g, 10 min, 4°C) and the supernatants were stored at Ϫ80°C until analysis.…”

“…Samples were centrifuged (3000 ϫ g, 10 min, 4°C) and the supernatants were stored at Ϫ80°C until analysis. The patients were identified as having pulmonary edema secondary to ALI or hydrostatic causes based on the edema fluid/plasma total protein ratio, as determined by the Biuret method, by clinical criteria (22,38,39), and by the simplified acute physiology score (SAPS II), which was calculated as described (40). Patients were identified as having ALI if the edema fluid/plasma total protein ratio was Ͼ0.65 and the patients had clinical criteria of bilateral infiltrates on a chest radiograph, PaO 2 /FIO 2 of Ͻ300 and a pulmonary capillary wedge pressure of Ͻ18 mm Hg, if measured, with clinical risk factor(s) for the development of clinical ALI (22,41).…”

“…The patients were identified as having pulmonary edema secondary to ALI or hydrostatic causes based on the edema fluid/plasma total protein ratio, as determined by the Biuret method, by clinical criteria (22,38,39), and by the simplified acute physiology score (SAPS II), which was calculated as described (40). Patients were identified as having ALI if the edema fluid/plasma total protein ratio was Ͼ0.65 and the patients had clinical criteria of bilateral infiltrates on a chest radiograph, PaO 2 /FIO 2 of Ͻ300 and a pulmonary capillary wedge pressure of Ͻ18 mm Hg, if measured, with clinical risk factor(s) for the development of clinical ALI (22,41). Patients were identified as having hydrostatic edema (HYDRO) if the edema fluid/plasma total protein ratio was Ͻ0.65 and the patients had a wedge pressure of Ͼ18 mm Hg or a two-dimensional echocardiogram demonstrating a reduced left ventricular ejection fraction and a clinical history consistent with cardiac dysfunction (22,41).…”

“…IL-1␤ was found to induce IL-6, which acted in an autocrine manner in concert with IL-1␤, to stimulate fibroblast proliferation (22). The observed IL-1␤/IL-6 responses did not, however, account for all of the proliferative bioactivity associated with the ALI edema fluid (22).…”

“…We found recently that pulmonary edema fluid from patients with early ALI induces a greater mitogenic effect than pulmonary edema fluid from patients with hydrostatic pulmonary edema and that this effect was mediated largely by IL-1␤ (22). IL-1␤ was found to induce IL-6, which acted in an autocrine manner in concert with IL-1␤, to stimulate fibroblast proliferation (22).…”