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H.C. Turner, J. Wolosin, M. Taveras; Expression, Localization and Secretion of Phospholipase A2 in Human Conjunctival Goblet Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4949.
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© ARVO (1962-2015); The Authors (2016-present)
Comparative corneal/conjunctival microarray analysis (Turner, ARVO 2004; #1462) identified group IIA secretory phospholipase A2 (sPLA2–IIA) a natural anti–microbial protein in tears, as a major component of the human conjunctival epithelium. Secretory PLA2 enzymes perform a wide range of other biological functions in a tissue–dependent manner that, in particular, includes an important role as a powerful proinflammatory mediator (Int Arch Allergy Immunol. 2003; 131:153). Given its high expression level in the conjunctiva, we examined the cellular distribution of sPLA2–IIA protein at the histological level to establish whether there is an anatomical basis for secretory activity.
Freshly frozen and formalin fixed, paraffin–embedded conjunctival tissue sections were probed with a mouse monoclonal antibody to human sPLA2 and visualized with an Alexa 488–conjugated secondary antibody using epiflourescent and confocal microscopy.
sPLA2–IIA was distributed in both Goblet (Gb) and non–Goblet (nGb) cells in vesicular structures. Staining intensity demonstrated that the majority of the enzyme was accumulated in the Goblet cell. In immature subsurface Gbs, the vesicles were dramatically concentrated in full proximity to the cell membrane. In surface Gbs undergoing degranulation, numerous vesicle profiles were observed migrating towards the cell secretory pit while vesicular density at the membrane wall was markedly reduced. Within the nGb lineage, sPLA2–IIA vesicles in the subsurface cells were also localized to the plasma membrane. However, in the superficial cells, the vesicles have migrated to the sub–apical cytosolic space.
This study reveals for the first time the presence of a vigorous non–mucin protein secretory activity in a Goblet cell. The results additionally suggest that the conjunctiva may be a substantial source of tear sPLA2–IIA vis a vis the assumed lacrimal gland source. The relative concentration and secretory activities of these two tissues deserve to be investigated.
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