Bone Marrow Derived Cells in the Cornea.

Abstract

Abstract: : Purpose: Recent immunological studies have established the presence of a significant population of resident bone marrow–derived leukocytes within the cornea. The purpose of this study was to quantify the number of bone marrow–derived cells in the normal corneal stroma and assess their response to corneal injury. Methods: Enhanced Green Fluorescent Protein (EGFP) expressing chimeric mice were generated by transplantation of bone marrow from EGFP⁺–C57BL/6 mice into lethally irradiated wild type mice. After 2–3 months recovery, the density of EGFP expressing bone marrow derived cells was assessed using laser confocal microscopy by counting the number of EGFP positive cells versus total cells stained by propidium iodide. The activity of bone marrow–derived cells was assessed in organ cultured, intact chimeric corneas by multiphoton confocal microscopy to collect 4–dimensional data sets (x,y,z,t). Recruitment of bone marrow–derived cells to the cornea was evaluated after scrape injury and phototherapeutic keratectomy. Results: EGFP cells as percent of total cells in the corneal stroma ranged from 6.3 ± 1.8% in central to 8.0 ± 1.6% in the peripheral cornea (n = 5 mice). EGFP cells also showed an anterior to posterior distribution with the highest percentage detected in the anterior peripheral cornea (10.8 ± 4.5%) and the lowest in the posterior–central cornea (5.5 ± 1.2%). Overall the density of cells ranged from 300–400 cells/mm². 4–Dimensional microscopy detected morphologically and behaviorally different types of cells within the stroma. Dendritic cells showed extension and retraction of dendrites and a slow amoeboid movement. Non–dendritic cells (the most frequent cell type in the stroma) were either small exhibiting rapid cell migration (> 11 µm/min) or large with markedly slower migration. Migration through the stroma also involved both lateral and axial (anterior/posterior) movement. Injury was associated with massive migration of EGFP cells into the cornea that peaked by 3 days after injury, but persisted beyond 14 days. Conclusions: Our results confirm earlier findings that the corneal stroma contains a significant population of bone marrow–derived cells that can exceed 10% of the total cell population. We show for the first time that these cells appear to be dynamically active in the stroma and that additional cells are recruited after injury. The dynamic behavior of resident bone marrow–derived cells suggest that they may play an early role in the response of the cornea to injury and participate in downstream regulation of corneal repair.

Keywords: cornea: stroma and keratocytes • wound healing • cornea: basic science