Purpose: Among different chemokines, monocyte chemoattractant protein-1 (MCP-1) plays an important role in inflammatory disorders of lung. In response to stimuli, MCP-1 increases its transcription as an immediate early gene. In this paper, we describe the MCP-1-enhanced green fluorescent protein(EGFP) transgenic mouse in which EGFP expression is driven by human MCP-1 promoter and mimics the MCP-1 expression in situ. Thus, the MCP-1 reporter mouse model is designed to facilitate a better understanding of its role in various diseases. We employed this mouse model in a pulmonary granulomatous inflammation model using intratracheal instillation of Sephadex (SDX) beads and compared the EGFP reporter expression to endogenous MCP-1 expression through the course of inflammation.
Procedures: We analyzed the temporal pattern of SDX-induced infiltration of inflammatory cells in lung and in bronchoalveolar lavage fluid (BALF). The changes in tissue fluorescence, gene, and protein expressions for both MCP-1 and EGFP were analyzed.
Results: SDX instillation caused massive infiltration of inflammatory cells in BALF and lung tissue at the end of day 3. There was an increase of fluorescence in SDX-treated lung and BALF cells. By using lipopolysaccharide-induced systemic inflammation model, increase of fluorescence was found in bone marrow Gr-1(+) cells with high Mac-1 expression. MCP-1 and EGFP gene expression and MCP-1 protein level were increased after day 1, peaked at day 3, and declined toward basal levels at day 5. In contrast, EGFP protein level peaked after day 3 and remained elevated after day 5. Immunohistochemical staining revealed the MCP-1 and EGFP expression primarily at alveolar macrophages, macrophages infiltrating the granulomatous lesions and in bronchiolar epithelial cells.
Conclusions: By using a pulmonary granuloma model, we showed that EGFP transgene reporter expression in MCP-1-EGFP mouse was correlated to the endogenous MCP-1 induction. The establishment of this mouse model will provide a valuable tool for monitoring the activation of monocytes/macrophages and facilitate the studies on the roles of MCP-1 gene in various inflammatory diseases.