Serial Imaging of Luciferase Positive Bone Marrow Stromal Cell Migration to Form Radiation Pulmonary Fibrosis

Abstract 4734

Thoracic irradiation of C57BL/6 mice leads to an acute reaction phase in the lungs characterized by increased cytokine production and inflammation days 1–14 post irradiation. This is followed by a latent period where inflammation, histologic appearance and cytokine response returns to control levels. The late reaction phase occurs 100+ days post irradiation and is characterized by organizing alveolitis/fibrosis and involves migration of marrow origin macrophages and proliferating mesenchymal stem cells (fibroblasts), a subpopulation which migrates from marrow to the lungs. To quantitate migration in real time, thoracic irradiated mice were either made chimeric for luciferase positive (luc+) whole marrow or were injected with cells from a positive luc+ bone marrow stromal cell line and serially imaged at day 7, 60 or 120 using an IVIS^.. 200 Optical Imaging System. As a control for migration to the lung, another group of mice received 20Gy to the right hind leg and 1.5 ×10⁶ luc+ bone marrow stromal cells i.p. Imaging of chimeric mice revealed luc+ cell lung migration only after day 120. C57BL/6NTac female mice that received 20Gy thoracic irradiation followed by an i.p. injection 1.5 × 10⁶ luc+ positive bone marrow stromal cells revealed no migration of luc+ cells to the lungs at day 7 or day 60. Furthermore there was no migration to 20Gy irradiated leg at any timepoint. In marked contrast, at the time of the late reaction phase, at day 100, fibrosis was revealed as an increase in luc+ cell migration in lungs. The lung fibrosis model in C57BL/6 mice combined with live imaging allows sequential measurement of the effect of agents which may alter migration of bone marrow cells that contribute to radiation pulmonary fibrosis.