Visualization of rapid recruitment of mast cells into inflammation lesion using an optical imaging with an enhanced firefly luciferase gene

Objectives Because mast cell is involved in various diseases such as allergy, inflammation, and cancer, sensitive and reliable imaging tools to non-invasively monitor their bio-distribution should be required for better understanding its biological role in living subject. Here, we attempted to monitor the rapid migration of mast cells to turpentine oil-induced inflammation in living mice using an enhanced firefly luciferase gene.

Methods The murine mast cell line (MC-9) expressing an enhanced firefly luciferase and Thy1.1 genes was established by retroviral infection, referred to as MC-9/effluc. The cell proliferation, phenotypes expression (c-Kit and FcεRI), level of degranulation and eicosanoids (LTC4 and PGD2) synthesis were examined to determine the effects of viral infection on mast cell function. Turpentine oil was intramuscularly administrated to hind leg of mice to establish inflammation model. Seven days later, mice received MC-9/effluc cells via tail vein, followed by bioluminescence imaging (BLI) immediately after the transfer. Inflamed tissues were removed to determine the localization of migrated mast cells and immunohistological analysis with anti-Thy1.1-specific antibody was performed.

Results No significant differences in cell proliferation and phenotypes expression were seen between parental MC-9 and MC-9/effluc cells. There were also no differences in degranulation and eicosanoids synthesis between the two groups. In vivo BLI showed their early distribution in the lung and spleen within 1h after the transfer. Surprisingly, the migration of MC-9/effluc cells to inflamed lesion were first monitored at as early as 1 min , peak migration at 3 min. The migrated mast cells was visualized in inflamed lesion for 60 min. BLI signal were only observed in liver but not in inflamed lesion at 24h . Consistent with in vivo results, immunohistological examination clearly revealed the localization of migrated MC-9/effluc cells in inflamed tissues.

Conclusions We successfully visualized the recruitment of mast cell to the inflammatory lesion in living subjects using an in vivo optical imaging with effluc reporter gene, suggesting that mast cells tagged with effluc gene may serve as a useful tool to better understand the biological role of mast cell in various pathophysiological environments in various pathologic conditions.