Identification of a novel macrophage population in the normal mouse corneal stroma.

PURPOSE To examine the normal murine corneal stroma for the presence of bone marrow-derived leukocytes. METHODS Wholemounts of paraformaldehyde-fixed corneal stroma from normal mice at 5 to 16 weeks of age were examined in single- and double-color immunomorphologic studies performed with confocal microscopy. The phenotype, morphology, distribution, and density of immunopositive cells were determined. RESULTS Numerous CD45(+) cells with pleomorphic and dendriform morphology were found within the pericentral and central region of the corneal stroma (200-300 cells/mm(2)). Dual-color immunostaining demonstrated that 100% of the CD45(+) cells coexpressed CD11b and 50% coexpressed F4/80. Approximately 30% of the total cells and 50% of the F4/80(+) cells coexpressed major histocompatibility complex (MHC) class II antigens. Very small to negligible numbers of cells expressed markers of dendritic cells (CD11c) or granulocytes (Ly6G). Markers for T-cells and NK cells were absent from the corneal stroma, indicating that all the cells identified in the stroma were of the myeloid lineage. CONCLUSIONS The normal murine corneal stroma contains a significant number of CD45(+) leukocytes. Most these cells express the CD11b marker, but not other dendrite, granulocyte, T-cell, or NK markers, placing them in the monocyte/macrophage lineage.