Topographical Distribution and Phenotype of Resident Meibomian Gland Orifice Immune Cells (MOICs) in Mice and the Effects of Topical Benzalkonium Chloride (BAK)

Meibomian gland orifices (MGOs) are located along the eyelid margin and secrete meibum into the tear film. The profile of resident innate immune cells (ICs) at this site is not well understood. The distribution and phenotype of resident ICs around MGOs in mice was investigated and herein defined as MGO-associated immune cells (MOICs). The effect of topical 0.1% benzalkonium chloride (BAK) on MOICs was also assessed. Eyelids from healthy CD11c^eYFP and Cx3cr1^gfp/gfp mice aged three or seven months were compared. ICs were identified as CD11c⁺, Cx3cr1⁺, and MHC-II⁺ using four-colour immunostaining and confocal microscopy. MOIC density was variable but clustered around MGOs. There were more CD11c⁺ MOICs in three-month-old compared with seven-month-old mice (three-month-old: 893±449 cells/mm² vs. seven-month-old: 593±493 cells/mm², p = 0.004). Along the eyelid margin, there was a decreasing gradient of CD11c⁺ MOIC density in three-month-old mice (nasal: 1003±369 cells/mm², vs. central: 946±574 cells/mm², vs. temporal: 731±353 cells/mm², p = 0.044). Cx3cr1-deficient mice had two-fold fewer MHC-II⁺ MOICs, suggesting a role for Cx3cr1 receptor signaling in meibomian gland surveillance. CD11c⁺ MOIC density was lower in BAK-exposed eyes compared to saline-treated controls, suggesting a change in homeostasis. This study provides novel insight into resident ICs located at MGOs, and their contribution to MG homeostasis.