Characterization of langerin-expressing dendritic cell subsets in the normal cornea

Purpose. In addition to Langerhans cells (LCs), other dendritic cells (CD11c ⁺) have recently been shown to express Langerin (c-type lectin). In skin, (non-LC) Langerin+ dendritic cells initiate adaptive immunity. However, whether such dendritic cells (DC) reside in the cornea, an immune-privileged tissue, is unknown. Methods. Normal C57BL/6 corneas were harvested for qRT-PCR analyses of Langerin expression in the epithelium versus stroma. Immunohistochemistry for Langerin was also performed. Single-cell preparations of epithelium versus stroma were FACS analyzed for CD11c, CD11b, and CD103 expression. Fluorescence microscopy of corneas from muLangerin-eGFP mice (in which all CD11c ⁺ Langerin ⁺ cells express eGFP), huLangerin-DTA mice (only LCs are constitutively deleted), and huLangerin-Cre eYFP-flox (only LCs express eYFP) was performed. Results. qRT-PCR, immunohistochemistry, and FACS analysis identified CD11c ⁺ Langerin+ cells in the epithelium and stroma. Similarly, corneas of muLangerin-eGFP mice contained eGFP ⁺ cells in the epithelium and stroma. However, FACS analysis indicated phenotypically differing CD11c ⁺ Langerin ⁺ populations in the epithelium (CD11b ^lowCD103 ^low) versus stroma (CD11b+CD103low). Additionally, corneas from huLangerin-DTA mice were devoid of Langerin+ cells in the epithelium but were detectable in the stroma. In corneas from huLangerin-Cre eYFP-flox, eYFP ⁺ cells were detectable in the epithelium but not in the stroma. Conclusions. The normal corneal epithelium is endowed with CD11c ⁺ Langerin ⁺ cells that are LCs, whereas the stroma is endowed with a separate population of (non-LC) Langerin+ DCs. These findings should henceforth facilitate the examination of Langerin-expressing DC subsets in the immunopathogeneses of conditions such as keratoconjunctivitis sicca, allergic keratoconjunctivitis, and corneal allograft rejection.