Abstract
Purpose: :
In recent years, evidence has emerged demonstrating a significant population of antigen-presenting cells (APCs) within the normal murine cornea, an immune-privileged site once thought to be devoid of such cells. However, the specific phenotype of APCs in the different layers and regions of the cornea remain incompletely defined. Thus, we investigated the phenotype and distribution of APCs within the normal cornea of mice whose cells constitutively express EGFP from the CD11c promoter.
Methods: :
Handheld in vivo confocal microscopy and two-photon confocal microscopy were used to image corneas of live Balb/c mice whose cells express EGFP from the CD11c promoter. Standard confocal microscopy was used to image whole mounts of corneas from these mice.
Results: :
CD11c+ dendritic cells (DCs) reside in the basal epithelium, many seemingly embedded in the basement membrane. Most DCs express MHC class II on at least some dendrites, which extended up to 50 µm in length and traversed up 20 µm tangentially nearly to the apical surface of the epithelium. The DC density diminished from peripheral to central cornea. Beneath the DCs and adjacent to the stromal side of the basement membrane reside CD11c-CD11b+ presumed macrophages that expressed low levels of MHC class II. Finally, MHC class II- CD11b+ cells filled the remainder of the stroma.
Conclusions: :
Our findings reveal a unique stratification of APCs within the normal murine cornea suggestive of progression from APC to barrier function. Moreover, the transparent cornea represents an easily accessible organ that is amenable to in vivo fluorescence imaging of cells with fluorescence too dim to be detected in other tissues.
Keywords: antigen presentation/processing • cornea: basic science • microscopy: light/fluorescence/immunohistochemistry