Secretory component of IgA: a marker for differentiation of ocular epithelium.

Secretory component (SC) was studied by indirect immunofluorescence of the ocular surface epithelium. We find that conjunctival epithelium produces this component, and that it is absent in the corneal epithelium. Conjunctival epithelium loses its SC staining within 1 to 2 days as it grows over a denuded corneal stroma. This implies a very rapid turn-off of the SC gene and rapid export of the gene product previously formed. However, conjunctival flap epithelium does not change its characteristic structure or functions. Vascularization of corneas resurfaced by conjunctival epithelium usually leads to a rapid reversal of both morphological and biochemical characteristics in the surface epithelium, as judged by the reappearance of goblet cells and positive staining for SC. Vascularization of normal corneas leaves the epithelium unchanged, so that neither goblet cells nor SC appear. Thus metaplasia of conjunctival to corneal epithelium is incomplete, permitting reversion to type under certain conditions.