CD209 can be found on human corneal dendritic cells. 35  CD26 is not expressed in normal conjunctival tissue, and has only been found, and then only weakly expressed, in vascular endothelial cells of conjunctival tissue from biopsies of vernal conjunctivitis patients. 37  The only report of CD66e in the conjunctiva was from patients with trachoma who had gene expression in their upper palpebral conjunctiva. 39  There are no reports of CD26 or CD66e in cornea or tears. CD13 has not been reported on conjunctival or corneal epithelial cells, but has been found on human corneal keratocytes. 43  9‐O‐acetylated sialic acid has been found in human tears and on human corneal mucin. 44  Heparan sulfate has been found on human cornea and conjunctiva cells.45, 46