Inflammatory Mediators Induce Aberrant Basal-Lateral β-Hexosaminidase Secretion and Up-Regulate Inflammatory Cytokine Expression in Rabbit Lacrimal Epithelial Monolayers

Abstract

Purpose: : Other workers have presented evidence indicating that environment stress can initiate ocular surface inflammation and engender an autoimmune process that propagates to the lacrimal gland (LG). Studying mechanisms that might link acute inflammation and failure of immunoregulation, we found that histamine (H) and serotonin (5-HT) cause significant cytopathology in ex vivo rabbit lacrimal acinar cell (RLAC) models and impair the ability to secrete Cl^- in response to acute stimulation with carbachol (CCh).

Methods: : RLAC were seeded onto Transwell^® polyester inserts at 5 x 10⁵ cells/ml to reconstitute epithelial monolayers. They were exposed overnight to H and 5-HT at 1 µM and 1 mM. Secretion of β-hexosaminidase catalytic activity to apical (AP) and basal (BL) media was measured under resting conditions and during acute stimulation with 100 µM CCh. Cytokine and GAPDH mRNA abundances were determined by real time RT-PCR with species-specific primers and probes.

Results: : H at 1 µM and 1 mM induced significant constitutive AP secretion and decreased AP secretion induced by acute CCh stimulation. 5-HT did not alter secretion at 1 µM, but at 1 mM it also increased constitutive AP secretion and decreased CCh-induced AP secretion. H at 1 µM increased both constitutive and CCh-induced BL secretion; at 1 mM effects were variable. 5-HT at 1 mM also increased both constitutive and CCh-induced BL secretion; at 1 mM effects were variable. H at 10 mM and 5-HT at 1 mM increased the relative abundances of mRNAs for IL-1β and prolactin (PRL).

Conclusions: : Overnight H and 5-HT, which may model exposure to numerous inflammatory mediator- and neuropeptide G protein-coupled receptor agonists, induce dysfunctional states characterized by aberrant BL secretion of β-hexosaminidase and increased expression of inflammatory cytokines. It is likely other proteins also become secreted to the stroma. As reported elsewhere, increased PRL expression can abrogate immunoregulation and promote autoreactive T_H1 effector cell proliferation.

Keywords: lacrimal gland • drug toxicity/drug effects • autoimmune disease