Wirtschafter J D, McLoon L K, Ketcham J M, Weinstock R J, Cheung J C
Department of Ophthalmology, University of Minnesota School of Medicine, Minneapolis, USA.
Trans Am Ophthalmol Soc. 1997;95:417-29; discussion 429-32.
The conjunctival epithelium performs an important role in the homeostasis and integrity of the eye. These cells need to be replaced in order to protect the integrity of the ocular surface. Epithelial cells are replaced from slow cycling stem cells which in turn produce transient amplifying cells that undergo further divisions before becoming mature conjunctival epithelial cells. The natural history of the bulbar palpebral conjunctival cells has not been previously described.
A single injection of bromodeoxyuridine (brdU), a thymidine analogue, was administered intraperitoneally to adult rabbits at a concentration of 50 mg/kg body weight. The rabbits were sacrificed at 1, 3, 5, and 7 days following the injections. The orbital contents including the eyelids were exenerated en bloc, frozen in a manner that maintained the orientation and continuity between the eyelids and globe and sectioned in a parasagittal plane. The tissue was stained immunohistochemically to detect brdU labeled conjunctival epithelial cells. The brdU-positive epithelial cells were counted in a series of 0.4 mm zones starting at the mucocutaneous junction of the eyelid and progressing through the fornix and bulbar conjunctiva. Rabbit eyelids and human eyelid surgical specimens were stained for cyclin D1, a marker for cells that are in the G1 phase of the cell cycle.
In both the upper and lower eyelids, the peak number of brdU labeled cells/0.4 mm zone was located at progressively greater distances from the mucocutaneous junction in the animals sacrificed at 1, 3 and 5 days respectively, and gone by 7 days. A focus of brdU-labeled conjunctival cells remained within 1-2 mm of the mucocutaneous junction at all post-injection intervals. Foci of cyclin 1-positive cells were found almost exclusively near the mucocutaneous junction, but not in the fornix.
The mucocutaneous junction of the conjunctival epithelium is a source of actively dividing transient amplifying cells that migrate toward the fornix at a rate of about 1.7 mm/day as replacement conjunctiva so that at least some conjunctival epithelial stem cells must be located near the mucocutaneous junction. The presence of cyclin D1 staining cells at the mucocutaneous junction supports this view. These results are not necessarily at variance with previous studies, but they do diminish the relative importance assigned the forniceal region in palpabral conjunctival homeostasis. Moreover, the mucocutaneous junction might provide a therapeutically significant source of replacement conjunctival cells. The transit time of conjunctival epithelial cells is about 6 days.
结膜上皮在眼的稳态和完整性中发挥着重要作用。这些细胞需要更新以保护眼表的完整性。上皮细胞由缓慢循环的干细胞替代，这些干细胞进而产生短暂扩增细胞，后者在成为成熟的结膜上皮细胞之前会进一步分裂。球结膜和睑结膜细胞的自然历程此前尚未被描述。
以50mg/kg体重的浓度给成年兔腹腔内单次注射溴脱氧尿苷（BrdU），一种胸腺嘧啶类似物。在注射后1、3、5和7天处死兔子。将包括眼睑在内的眼眶内容物整块取出，以保持眼睑与眼球之间的方向和连续性的方式冷冻，并在矢状旁平面切片。对组织进行免疫组织化学染色以检测BrdU标记的结膜上皮细胞。从眼睑的黏膜皮肤交界处开始，以一系列0.4mm的区域计数BrdU阳性上皮细胞，这些区域依次穿过穹窿和球结膜。对兔眼睑和人眼睑手术标本进行细胞周期蛋白D1染色，细胞周期蛋白D1是处于细胞周期G1期细胞的标志物。
在上下眼睑中，分别在注射后1、3和5天处死的动物中，每0.4mm区域内BrdU标记细胞的峰值数量位于距黏膜皮肤交界处逐渐更远的位置，到7天时消失。在所有注射后的时间间隔内，BrdU标记的结膜细胞焦点始终位于黏膜皮肤交界处1-2mm范围内。细胞周期蛋白D1阳性细胞焦点几乎仅在黏膜皮肤交界处附近发现，而不在穹窿处。
结膜上皮的黏膜皮肤交界处是活跃分裂的短暂扩增细胞的来源，这些细胞以约1.7mm/天的速度向穹窿迁移作为替代结膜，因此至少一些结膜上皮干细胞必定位于黏膜皮肤交界处附近。黏膜皮肤交界处存在细胞周期蛋白D1染色细胞支持了这一观点。这些结果不一定与先前的研究不一致，但它们确实降低了穹窿区域在睑结膜稳态中所赋予的相对重要性。此外，黏膜皮肤交界处可能提供具有治疗意义的替代结膜细胞来源。结膜上皮细胞的迁移时间约为6天。
