Abstract
Abstract: :
Purpose:To compare markers for identification of human corneal stem cells, to clarify controversies concerning their use, and to lay a foundation for identification of stem cells in culture. Methods:Corneal sections (frozen or paraffin–embedded) from 20 donors (age 32–92, post mortem times 3–22h) were differently processed and stained with commercially available antibodies (Ab) against p63, ABCG–2, connexin 43 (Cx43), nestin, alpha enolase, keratin K3 and Ki –67. Results:For p63, ABCG–2 and nestin, staining patterns were largely dependent on tissue processing, source of the particular Ab, and individual donor. Nuclear p63–staining was mainly localized to single cells or cell clusters in the limbal basal epithelium (in 90% of donors), but also to suprabasal limbal and basal corneal epithelial cells (in 50% of donors). It appeared to colocalize partly with the proliferation marker Ki–67. Membranous staining for ABCG–2 was confined to groups of limbal basal cells and not found elsewhere. Subpopulations of basal limbal cells were Cx43 negative, whereas suprabasal cells showed faint positivity along their cell membranes. Double labeling showed that both p63 and ABCG–2 positive limbal basal cells did not express Cx43. Conclusion: The controversy about stem cell markers may have resulted from high interindividual variation in staining patterns and from different methodologies applied. Using various techniques and tissues, the current findings suggest that limbal progenitor cells can be identified by combining antibodies to ABCG–2, Cx43 and p63. However, clusters of ABCG–2(+)/Cx43(–)/p63(+) cells represent much more than 10% of all limbal basal cells and therefore exceed the number of putative stem cells. This indicates either a unique distribution pattern of corneal epithelial stem cells or inadequate staining with available markers.
Keywords: cornea: basic science • cornea: epithelium