Chronic IL-1beta and IL-6 Decrease Cl- Secretion in a Novel Rabbit Lacrimal Epithelial Monolayer Model

Abstract

Purpose: : Lymphocytic infiltration may be associated with decreased lacrimal gland (LG) fluid production and dry eye disease. However, deficits range from profound functional quiescence in patients with Sjögren’s dacryoadenitis to minimal dysfunction in some subjects with common, age-related lacrimal histopathology. Laboratory studies suggest that agonistic muscarinic acetylcholine receptor (M3AChR) autoantibodies, inflammatory cytokines, and inflammatory mediators that activate G protein-coupled receptors (GPCR) inhibit LG protein secretion. We recently described a rabbit lacrimal acinar cell monolayer (RLACM) model that makes it possible to address mediator influences on the ion transport processes that underlie LG fluid production. We have now used RLACM to learn how chronic exposure to IL-1β, IL-6, and low-dose carbachol (CCh), a surrogate for agonistic M3AChR autoantibodies, affect LG Cl^- secretion.

Methods: : Purified RLACs were seeded onto polyester membrane inserts at a density of 5 x 10⁵ cells/ml. The RLACM were mounted in Ussing chambers for measurement of short-circuit currents (I_sc).

Results: : RLACM spontaneously generated small baseline BL→AP I_sc, presumably associated with either Cl^- absorption or Na⁺ secretion. As previously reported, acute stimulation with 100 µM CCh induced large AP→BL I_sc reflecting Na⁺-dependent Cl^- secretion. After RLACMs were exposed to low-dose CCh overnight, acute stimulation with 100 µM CCh either had no effect or increased the BL→AP I_sc. Overnight exposure to IL-1β at 1 ng/mL had variable effects, but at 10 ng/mL it decreased CCh-induced AP→BL I_sc by 50%. Inhibition of CCh-induced AP→BL I_sc by chronic exposure to IL-6 was variable but never exceeded 40%.

Conclusions: : Chronic exposure to agonistic M3AChR autoantibodies may account for the profound quiescence of LG exocrine function in patients with Sjögren’s syndrome, while chronic exposure to inflammatory cytokines may account for less severe dysfunction in cases of dacryoadenitis without autoantibody production.

Keywords: lacrimal gland • cytokines/chemokines • electrophysiology: non-clinical