Kinetics of polymorphonuclear leukocytes in an experimental hypopyon model

Regarding the process of uveitis development, many past studies have used the experimental autoimmune uveoretinitis (EAU) and other animal models to observe histologically the infiltration of inflammatory cells and the process of lesion progression. However, no detailed study of the process of clearance of infiltrated inflammatory cells from the eye has been reported. The purpose of this study was to investigate the process of clearance of polymorphonuclear leukocytes (PMNs) using an experimental hypopyon model. PMNs obtained from ascites of SD rat were injected into the anterior chamber of SD rats. The process of PMNs clearance was evaluated by serial photography and 3D optical coherence tomography (3D-OCT), and histological changes were observed simultaneously. The hypopyon heights regressed from 1.04±0.06 mm at 1h (day 0) to 0.45±0.07 mm at day 1, and 0 mm at day 3 after PMNs injection. When the hypopyon heights at the three time points were compared, significant differences were found between groups (P<0.05). The hypopyon volumes also decreased from 1.46±0.07 mm(3) at 1h to 1.16±0.09 mm(3) at 2h, and 0.83±0.04 mm(3) at 3h after PMN injection. When the hypopyon volumes at the three time points were compared, significant differences were found between groups (P<0.05). Light micrographs of inferior segment of the eyeball revealed dense PMNs in the chamber angle at 1h after PMNs injection and many PMNs in the iris stroma and vessels, as well as at the episcleral and subconjunctival tissues around limbus at 3h and day 1 after PMNs injection. Light micrographs of superior segment of the eyeball at 3h after injection revealed PMNs in the episcleral and subconjunctival vessels. Electron micrographs of inferior segment of the eyeball at 3h after PMNs injection revealed dense PMNs with slightly condensed nuclei in the anterior chamber, as well as in the iris stroma and vessels. In conclusion, in the experimental hypopyon model, PMNs injected into the anterior chamber were cleared from the eye mainly through the iris stroma and vessels, as well as the episcleral and subconjunctival tissues around limbus.