Objectives: To determine whether selective laser trabeculoplasty (SLT) induces monocyte recruitment to the trabecular meshwork (TM) in human and monkey eyes and whether monocytes increase both aqueous outflow in vivo and the conductivity of human Schlemm canal endothelial cells (SCEs) in vitro. Methods: Monocyte recruitment was examined morphometrically in control human and monkey eyes and compared with that following SLT applied 1 to 3 days earlier. Outflow facility was measured for up to 4 days after the intracameral infusion of autologous macrophages in rabbits. Schlemm canal endothelial cell conductivity was measured using flow meters after exposing cultured SCEs to monocytes and monocyte-secreted factors for 24 hours. Results: Our estimates show that the TM in the human eye normally had an average of 15 003 monocytes, while in the monkey eye there were 3181 monocytes, and this number increased 4- to 5-fold following SLT. The intracameral infusion of autologous macrophages in rabbits increased outflow facility 2-fold in a rapid and sustained manner. Human monocytes and monocyte-secreted factors increased SCE conductivity 2-fold in vitro. Conclusions: The number of monocytes/macrophages in the TM increases substantially after SLT and monocytes augment both outflow facility and SCE conductivity. Clinical Relevance: These findings indicate that the innate immune system in general and monocytes in particular play an important role in aqueous outflow homeostasis. The recruitment of monocytes in increased numbers after SLT likely plays a role in lowering the intraocular pressure after this procedure. The intracameral introduction of autologous monocytes harvested from a vein could have therapeutic potential as a cell-based individualized treatment of glaucoma.
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