Type 3 keratin was expressed in full-thickness corneal epithelium and suprabasal limbal epithelium (not shown). It was also expressed by the suprabasal oral mucosal epithelium
(Fig. 3A) . Of interest, full-thickness K3 staining was observed in cultivated keratinocytes
(Fig. 3D)as well as in all corneal specimens
(Figs. 3B 3C 3E 3F) . Keratin 12, a more specific marker for differentiated corneal epithelium was seen in the full thickness of normal corneal and suprabasal limbal epithelium
(Figs. 4A 4D) , but was not seen in patients 1, 3 and 4
(Figs. 4B 4E 4F) . Of interest, the left peripheral portion of patient 2 showed full-thickness K12 staining
(Fig. 4C) , whereas K13 staining in the adjacent OMECs was positive in the suprabasal area (
Fig. 4A , inset). This finding implies a mixture of oral mucosal and corneal epithelium in the cornea of patient 2. K4 is the keratin paired with K13 and can be expressed by the suprabasal epithelia of normal oral mucosa (
Supplementary Fig. S1A), normal cornea (
Supplementary Fig. S1B), and corneal specimens from patients 1 and 2 (Supplementary Figs. S1E, S1F), but it was expressed only in the superficial layers of normal conjunctiva (Supplementary Fig. S1C) and cultivated OMECs (Supplementary Fig. S1D). K13 is a mucosa-specific keratin, and its expression was constantly suprabasal all in normal oral mucosa (Supplementary Fig. S2A), cultivated OMECs (Supplementary Fig. S2D), and all corneal specimens (Supplementary Figs. S2B, S2C, S2E, S2F). Supplementary Figures S2B and S2E clearly show that the basal small-cell zone was K3 negative. K8 staining was positive both in the normal corneal
(Fig. 5A)and conjunctival epithelium
(Fig. 5B) , and also in the removed pannus of patients 3 (not shown) and 4
(Fig. 5C)during COMET. Of note, its expression was consistently negative in the normal oral mucosa
(Fig. 5D) , cultivated OMECs (not shown), and all corneal specimens
(Figs. 5E 5F) .