Monocyte chemotactic factors released from type II pneumocyte-like cells in response to TNF-alpha and IL-1alpha

Abstract

It has been reported that tumour necrosis factor (TNF)-a and interleukin (IL)-1 induce the release of monocyte chemotactic factors (MCF), including chemokines, from A549 cells, an alveolar type II cell line. However, the relative contribution of these chemokines to MCF is still uncertain.In the present study, the relative contribution of various chemokines released from A549 cells acting as MCF upon stimulation by TNF-a and IL-1a, was evaluated.TNF-a and IL-1a induced the release of MCF in a dose-and time-dependent manner (p<0.001). The release of MCF was inhibited by cycloheximide and lipoxygenase inhibitors. Molecular sieve column chromatography revealed multiple peaks of MCF (near 60 kDa, 25±22 kDa, 15±13 kDa, 8 kDa, and 400 Da). Leukotriene B 4 (LTB 4 ) receptor-antagonists inhibited MCF by 50% after 24 h and 30% after 72 h. Monocyte chemoattractant protein-1 (MCP-1), transforming growth factor (TGF)-b, "regulated on activation, normal T-cells, expressed and secreted" (RANTES), and granulocyte-macrophage colony-stimulating factor (GM-CSF) were released significantly in response to IL-1a and TNF-a, and antibodies to MCP-1, GM-CSF, and RANTES inhibited MCF activity by 40, 5 and 20% after 24 h, and by 50, 20, and 10% after 72 h, respectively. Each antibody or LTB 4 receptor-antagonist inhibited the corresponding column chromatography-separated molecular weight peak of MCF.These data suggest that A549 cells release monocyte chemoattractant protein-1 as the predominant monocyte chemotactic factor rather than granulocyte-macrophage colony-stimulating factor, RANTES, and transforming growth factor-b, and that leukotriene B 4 is constitutively released as a monocyte chemotactic factor. Eur Respir J 1999; 13: 820±828. The alveolar macrophage, an important phagocyte of the pulmonary airspace and the interstitium, is derived predominantly from differentiated peripheral blood monocytes and to a limited extent from local macrophage replication [1±3]. The recruitment of peripheral blood monocytes to the lung is essential for normal lung immune function but it is also involved in the generation and evolution of an inflammatory response to pulmonary injury. During acute and chronic inflammation, the process of monocyte elicitation is accelerated resulting in a transient or more prolonged increase in alveolar macrophages [4,5]. Although elicited macrophages serve a vital role in the host defence against a number of organisms, the presence of increased numbers of activated macrophages can lead to excessive tissue injury via excessive elaboration of inflammatory cytokines, eicosanoids, proteolytic enzymes, and oxygen radicals [6±8].Alveolar type II (ATII) epithelial cells have been shown to play a significant role in the regulation of the alveolar space. ATII cells synthesize and secrete surfactant, control the volume and composition of the epithelial lining fluid, and proliferate and differentiate into type I alveolar epithelial cells after lung injury in order to maintain the integrity of alveolar wall [9]. Moreove...

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