Abstract
Purpose: :
To study the distribution of the cells derived from leukocytes in the eyes of chimeric mice transplanted with enhanced green fluorescent protein (EGFP)-positive bone marrow cells.
Methods: :
Adult C57BL/6 mice were lethally irradiated and injected with EGFP-positive bone marrow cells intraperitoneally. One to twelve month after bone marrow transplantation (BMT), the eyes were enucleated, processed into cryosections or cilio-retinal flat-mounts, and analyzed immunohistochemically using anti-F4/80, anti-Iba1, and anti-MHC class II antibodies and GS-1 lectin. The distributions of EGFP-positive cells in the eyes with and without retinal injury were determined. N-methyl-N-nitrosourea (MNU) was injected or partial retinal detachment (RD) was created to induce retinal injury.
Results: :
Small numbers of EGFP-positive cells were found in the ciliary body, retinal pigment epithelium, and choroid and around the optic nerve in the uninjured eyes. Such cells existed in the peripapillary and peripheral retina at 3 and 6 months after BMT, respectively. Most of them were immuno-positive for anti-F4/80 antibody and anti-Iba1 antibody and showed characteristic morphology of microglias. However, in the eyes with MNU-induced retinal injury, a large number of EGFP-positive cells were found around the retinal vessels, optic nerve, and ciliary body, which rapidly spread into the retina. Most of them appeared to be microglias based on their morphology and immunohistochemial profile. In this model, microglias immuno-positive for EGFP and Iba1 accounted for approximately 15% of total Iba1-positive microglias in the injured retina. Meanwhile, the proportion of MHC class II-positive cells was larger among EGFP-positive cells than total Iba1-positive cells. In the eyes with RD, many cells positive for EGFP and F4/80 were identified exclusively in and under the detached retina.
Conclusions: :
In uninjured eyes, minimal bone marrow-derived cells were found in the retina. However, in response to retinal injury, numerous bone marrow-derived cells migrated into the retina most of which differentiated into microglias. Higher rate of immunological activation and increased specificity to the injury site appeared to be the features of bone marrow-derived microglias.
Keywords: microglia • retinal degenerations: cell biology • retina