Ocular Surface Expression of Glycoprotein–340 and Surfactant Protein–D.

Abstract

Abstract: : Purpose: Glycoprotein 340 (GP–340) is a member of the scavenger receptor cysteine rich group B family, acts a salivary agglutinin, and, as determined by MALDI–TOF, is present in tears. Surfactant protein D (SP–D) is a component of the lung surfactant complex and a member of the collectin family of proteins. SP–D is widely expressed in mucosal epithelia and has been detected in human and mouse lacrimal glands. SP–D is a mannose binding lectin and is itself bound by GP–340. The current study examines the expression of these protective proteins in ocular surface tissues including cornea, conjunctiva and lacrimal gland. In addition we examined normal human tear fluid for mature gp–340 and SP–D protein. Methods: RT–PCR was used to determine if human cornea, conjunctiva and lacrimal gland produce mRNAs specific for gp–340 and SP–D as well as other known surfactant proteins (SP–A, SP–B, SP–C). Western blot analysis was used to detect the corresponding protein in human tissue extracts and tears. To determine the relative abundance of gp–340, Western blots of serial dilutions of tears and saliva were evaluated. Results:Transcripts of SP–A, SP–B and SP–C were not detected in any human ocular tissues. SP–D and gp–340 transcripts were present in RNA extracted from cornea, conjunctiva and lacrimal gland. Western blot analysis shows that gp–340 and SP–D are present in human tear film and that gp–340 is considerably more abundant in tears than in saliva. Conclusions: This is the first demonstration that both gp–340 and SP–D are produced by a variety of ocular surface mucosal tissues and that these proteins are components of the normal tear film. SP–D is a multifunctional, lipophilic, calcium dependent carbohydrate binding protein, originally isolated from lung. SP–D has been shown to interact with secreted lipids, to opsonize bacterial pathogens and to modify inflammatory responses. Gp–340 binds SP–D and is taken up by dendritic cells and macrophages. These proteins are likely to protect the corneal and conjunctival mucosa and to link the innate and adaptive immune systems of the ocular surface mucosae.

Keywords: conjunctiva • cornea: tears/tear film/dry eye • lacrimal gland