Paracrine Interactions between the Conjunctival and Corneal Epithelial Cells Regulate Microenvironmental Homeostasis during Artificially Induced Inflammation.
Purpose/Aim of the study: The corneal and conjunctival epithelium interact with each other and reciprocally modulate the levels of soluble mediators to maintain balance in the ocular surface. The aim of the present study was to analyze paracrine interactions between the corneal and conjunctival epithelium in an inflamed microenvironment (LPS or PMA induction) to test the levels of pro- and anti-inflammatory cytokines and nitric oxide released by the epithelia. The corneal (pRSV-T) and conjunctival (HC0597) epithelial cell cultures and their indirect co-cultures were treated for 2 h with LPS (E. coli) or for 30 min with phorbol 12-myristate-13-acetate (PMA) to induce inflammation. Cytokine expression (IL-1β, IL-6, IL-10) and the level of apoptosis were analyzed by ELISA, and the nitric oxide (NO) level by Griess reaction. Cells were incubated for 24 h. The apoptosis of the corneal and conjunctival epithelia decreased (by 43% and 53%, respectively) in co-cultures compared to corresponding monocultures. The conjunctival epithelium produced lower amounts (23%) of NO than the corneal epithelium. PMA and LPS had comparable effects on the levels of NO in mono- and co-cultures. The levels of the tested cytokines changed depending on the type of cell culture and culture conditions (mono- vs. co-cultures and inflammation). The most striking changes were observed for IL-6 expression. Paracrine interactions between the corneal and conjunctival epithelia may regulate microenvironmental homeostasis during artificially induced inflammation among others by balancing the levels of NO, cytokines, and the viability of cells.