Characteristic morphology and distribution of bone marrow derived cells in the cornea

Enhanced green fluorescence protein (eGFP)-labeled bone marrow (BM) cells were transplanted into syngeneic C57BL/6 (wild-type) mice to investigate the distribution pattern, immunohistochemical characteristics, three-dimensional structure, and ultrastructure of the BM-derived cells in the mouse cornea using a fluorescence microscope, a confocal laser scanning microscope, and a transmission electron microscope. This study provided direct evidence that two morphologically distinct types of BM-derived cells were distributed in the mouse cornea. The majority of the GFP+ cells showed a flattened polygonal form with obtuse angles and these cells were distributed in the corneal stroma. The other type was the GFP+ cells demonstrating slim cell bodies with long and extremely thin dendrites and which were distributed in the corneal epithelium. The immunohistochemical characteristics and ultrastructure of BM-derived cells suggest that most of these cells have a macrophage lineage, whereas some cells in the corneal stroma do not. Interestingly, the direct intimate contact between GFP-labeled BM derived cells and non-GFP-labeled resident cells within the corneal stroma were also clearly visualized at the fine structural level. These data provide new and more detailed insight into the nature of BM-derived cells in the cornea.