PRODUCTION OF TUMOUR NECROSIS FACTOR α BY PRIMARY CULTURED RAT ALVEOLAR EPITHELIAL CELLS

Tumour necrosis factor α(TNF-α) is one of the most important pro-inflammatory cytokines, which plays an important role in host defense and acute inflammation related to tissue injury. The major source of TNF-α has been shown to be immune cells such as macrophages and neutrophils. In the present study, we demonstrated that LPS-treatment on alveolar epithelial cells isolated from adult rat lungs also induced a dose- and time-dependent release of TNF-α. The purity and identity of these cells were examined by immunofluorescent staining and confocal microscopy with antibodies for cytokeratin and pro-surfactant protein C, markers for epithelial cells and type II pneumocytes respectively. Positive staining of TNF-α was observed throughout the cell layer and localized intracellularly. LPS-induced TNF-α production from alveolar epithelial cells was blocked not only by cycloheximide, an inhibitor of protein translation, but also by actinomycin D, an inhibitor of gene transcription. The mRNA of TNF-α rapidly increased within 1h of LPS stimulation. These data suggest that LPS-induced TNF-α production from alveolar epithelial cells is primarily regulated at the transcriptional level, which is different from that of macrophages and neutrophils. TNF-α produced by alveolar epithelial cells may function as an alert signal in host defense to induce production of other inflammatory mediators.