Characterization of bone marrow derived cells in the substantia propria of the human conjunctiva

To characterize the main population of bone marrow-derived cells (BMCs) in human normal subconjunctiva and make a comparison with BMCs in the corneal stroma and epithelium.

Normal human donor corneas with attached conjunctiva were examined by fluorescence microscopy after single and double staining for multiple markers. CD68(+) cells were separated from the conjunctival tissues by using magnetic beads, and the expression of toll-like receptor (TLR) 2 and TLR4 was examined. Surface markers of CD68(+) cells were compared with those of BMCs from the corneal stroma and epithelium.

CD45(+) cells were detected in the substantia propria of the conjunctiva, and approximately 60% of these cells were CD68(+). All the CD68(+) cells expressed HLA-DR and CD14. CD68(+) cells isolated from conjunctival tissues expressed TLR2 and TLR4 on flow cytometry. BMCs in both the corneal stroma and the subconjunctiva expressed scavenger receptor CD163. Macrophage mannose receptor CD206 was expressed by BMCs in the substantia propria of the conjunctiva, but not by BMCs in the corneal stroma or epithelium.

These findings demonstrated that the main population of BMCs in the substantia propria of normal human conjunctiva is CD68(+)CD14(+)HLA-DR(+) cells. These BMCs express scavenger receptor, macrophage mannose receptor, TLR2, and TLR4 and may play a role in adaptive and innate immune responses in the human ocular surface. These cells are phenotypically different from the CD68(-)CD206(-) monocyte- lineage cells found in the corneal stroma and the CD11c(+)CD68(-)CD163(-)CD206(-) dendritic cells residing in the corneal epithelium.