The corneal stroma is endowed with a significant number of resident dendritic cells

Dendritic cells (DCs) comprise a system of highly efficient antigen-presenting cells (APCs) that initiate immune responses. The purpose of this study was to examine the normal stroma for the presence of DCs and other bone marrow (BM)-derived cells.

Normal uninflamed corneas of BALB/c and other murine strains were excised, and immunofluorescence single- and double-staining for multiple markers was performed for examination by confocal microscopy. Corneal buttons were placed in culture and immunocytochemistry and flow cytometry performed.

MHC class II(+)CD80(+)CD86(+) cells were found in the periphery of the anterior normal stroma. These cells were CD45(+), CD11c(+)CD11b(+) suggesting a BM-derived and monocytic DC lineage. In a surprising finding, significant numbers of MHC class II(-)CD80(-)CD86(-) cells were found in the center of the anterior stroma. These cells were also CD45(+)CD11c(+)CD11b(+) but CD3(-), GR-1(-), keratan sulfate(-), and CD8alpha(-), reflecting an immature precursor phenotype of myeloid DC. In addition to DC subsets in the anterior stroma, a CD11c(-)CD11b(+) population of BM-derived cells was found primarily in the posterior stroma, representing monocytes/macrophages. These cells were rarely present in the anterior third of the normal stroma. Further, CD14(+) precursor-type DCs were found throughout the stroma. These in vivo findings were not strain specific and were confirmed by immunocytochemistry and flow cytometry analyses of cells derived from corneal explants and by transmission electron microscopy.

This study demonstrates that, in addition to the known Langerhans cells in the corneal epithelium, at least three BM-derived cell subsets reside in the normal corneal stroma.