The proinflammatory cytokines and arachidonic acid metabolites in human overnight tears: homeostatic mechanisms

Abstract

The tear film plays an important role in the defense of the external ocular surface. During sleep a number of changes take place, including increased production and release of various inflammatory mediators. We have studied the hypothesis that closed-eye tears contain proinflammatory cytokines and lipid inflammatory mediators, which serve to recruit polymorphonuclear leukocytes (PMNs) and regulate the function of PMNs and IgA during sleep. We investigated interleukin-1beta, interleukin-6, interleukin-8, monocyte chemotactic protein 1, granulocyte-macrophage colony stimulating factor (GM-CSF), leukotriene B4 (LTB4), and platelet activating factor (PAF) in open and closed-eye tears of normal healthy subjects. Results showed that IL-6, IL-8, GM-CSF, LTB4, and PAF were present in high levels in closed-eye tears compared to open-eye tears. Closed-eye tears were able to recruit neutrophils, with maximal recruitment after 8 hr of sleep, suggesting that chemokine IL-8 and the lipid chemoattractant LTB4 were active. Flow cytometric analysis revealed that incubation of neutrophils with closed-eye tears up-regulated the surface expression of IgA receptor, indicating that the GM-CSF in tears was functionally active. Up-regulation of cytokines and the lipid inflammatory mediator LTB4 during eye closure are noteworthy, as each of these cytokines has an established role in initiation and amplification of the inflammatory response. IL-8 and LTB4 may act as potent chemoattractants and activators for PMNs, whereas IL-6 and GM-CSF potentiate the secretion and function of IgA and enhance neutrophil responsiveness to proinflammatory agonists.