Abstract
Purpose: :
A single cell layer of epithelial downgrowth on the cornea may be difficult to differentiate from endothelium. Currently, anti-cytokeratin AE1/AE3 (pankeratin AE13) is is the most commonly used immunohistochemical marker to confirm epithelial downgrowth. Prior observations prompted us to test the hypothesis that MUC16 is a more specific marker for epithelial downgrowth compared to pankeratin AE13. In addition anti-cytokeratin 19 (CK19) reactivity was used to determine if the causative cells were derived from conjunctival epithelium.
Methods: :
For direct comparison, six epithelial downgrowth and six control corneal specimens were embedded in the same paraffin block. Five micron sections were stained immunohistochemically for MUC16, pankeratin AE13, and CK19 using the immunoperoxidase method. The numbers of reactive cells/total cells were counted on the epithelial and endothelial surfaces at a magnification of 250x under a compound microscope. The mean percentages of reactive cells were compared for each antibody and data were analyzed using the Wilcoxon rank-sum test.
Results: :
In control corneas MUC16 was expressed only in the superficial layers of the epithelium, but pankeratin AE13 was expressed by the majority of the epithelium ( percent of total cells reactive 7.3% ± 9.5% vs. 78.7% ± 61.2%, P < 0.004). None of the endothelial cells showed any reactivity to anti-MUC16 compared to the surprising endothelial reactivity to anti-pankeratin AE13 (0.0% ± 0.0% vs. 18% ± 9.5%, P < 0.0006). Epithelium in all downgrowth specimens was reactive for MUC16 and pankeratin AE13 on both corneal surfaces. There was no significant difference in the percentage of epithelial cells positive for MUC16 versus pankeratin AE13 on the endothelial surfaces. CK19 was positive in 17.2% ± 15.3% cells on the epithelial surface and 44.1 ± 43.7% of cells on the endothelial surface in cases of downgrowth.
Conclusions: :
MUC16 expression is a highly sensitive and specific immunohistochemical marker for the diagnosis of epithelial downgrowth. Pankeratin AE13 is a sensitive but less specific marker that could result in false positive interpretation of epithelial downgrowth. The expression of CK19 supports a conjunctival origin for cells responsible for epithelial downgrowth.
Keywords: immunohistochemistry • cornea: epithelium