Intercellular signaling plays an important role in the development of lung ischemia–reperfusion injury. However, the role of specific mediators remains poorly characterized. Alveolar macrophages (AM) produce soluble mediators early in reperfusion, which modulate the responses of endothelial and epithelial cells to oxidative stress. There is a burst of proinflammatory cytokine production in a variety of cells; however, interleukin 1-beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) localize to the AM. We hypothesized that these cytokines account for the costimulatory effects that AM exert on endothelial and epithelial cells.

Activated AM media was placed on cultured rat type 2 pneumocytes and pulmonary artery endothelial cells, which were then subjected to hypoxia and reoxygenation. To assess the contributions of IL-1β and TNF-α, the cells were treated with control media or media that had been depleted of IL-1β or TNF-α. To deplete specific cytokines, activated media was passed through a column with immobilized IL-1β or TNF-α antibodies. Nuclear translocation of transcription factors, mitogen-activated protein kinase activation, and cytokine and chemokine production were assessed.

Depletion of IL-1β or TNF-α effectively eliminated the ability of AM media to enhance the response of endothelial and epithelial cells to oxidative stress. There were significant reductions in monocyte chemotactic protein 1 and cytokine-induced neutrophil chemoattractant (CINC) production (p < 0.05) at 4 hours of reperfusion. Additionally there was decreased nuclear translocation of nuclear factor-kappa B, and extracellular signal-regulated kinase phosphorylation.

Interleukin 1-beta and TNF-α are critical mediators in the intercellular communication pathways that allow the AM to enhance the response of surrounding cells to oxidative stress.