Enrichment of Lymphatic Vessel Endothelial Hyaluronan Receptor 1 (LYVE1)-Positive Macrophages Around Blood Vessels in the Normal Human Sclera

Abstract

To investigate whether the normal adult human sclera contains lymphatic vessels and to study their relation to immune cells and blood vessel anatomy. Scleral tissue probes from 35 adult human donor bulbi were analyzed by immunohistochemistry and confocal microscopy for blood vessels (CD31+), lymphatic vessels (lymphatic vessel endothelial hyaluronan receptor 1 [LYVE1]+, podoplanin+), and macrophages (CD68+) at 12 locations (anterior, equatorial, and posterior at 3, 6, 9, and 12 o'clock positions of the eye) in all three scleral layers (episclera, stroma, and lamina fusca). Approval for scientific examination was obtained. CD31+ blood vessels were detectable in the human sclera, where the percentage area covered by CD31+ blood vessels was highest in the anterior episclera, followed by equatorial and posterior episclera, and was lowest in the scleral stroma (regardless of location). LYVE1+ podoplanin+ lymphatic vessels were not detectable in any location investigated, although there was a high number of LYVE1+ CD68+ macrophages. These macrophages were concentrated around blood vessels. In contrast, in the episclera, the number of detected LYVE1+ CD68+ macrophages was comparable in all locations; within the stroma, their number increased toward the posterior part of the eye. The adult sclera contains blood vessels but lacks, as revealed by immunohistochemistry and confocal microscopy, true lymphatic vessels. LYVE1+ CD68+ macrophages are located adjacent to the longitudinal axis of blood vessels. The function of these cells needs further investigation, but could be a next step toward a better understanding of pathological disorders such as inflammation, tumor, trauma, or glaucoma.