Abstract
Purpose::
Laser induced retinal burns trigger gliosis that results in retinal scarring. IFN-γ is a pro-inflammatory cytokine that activates microglia/macrophage and also increases glial cell activation. We hypothesize glial scarring and retinal dysfunction caused by laser burns is augmented when inflammatory cells release IFN-γ and activate microglia.
Methods::
C57BL/6 mice received 4 laser burns (spot size: 125 microns, duration time: 100 msec, and energy: 100 mW) one disc diameter from the optic nerve. Healing of the laser burns and formation of glial scars was monitored by: (i) clinical observation via fundus camera, (ii) fluorescein angiography, (iii) histology, (iv) immunohistochemical staining of Muller cells and microglia ,and (v) ERG (b-wave ratio).
Results::
In order to determine the role of IFN-γ in gliosis following retinal laser burns, we examined the healing of retinal wounds in either: (i) wild-type mice, (ii) IFN-γ KO mice, (iii) wild-type mice that received an intravitreal injection of recombinant IFN-γ immediately after laser treatment, or (iv) mice that received a similar intravitreal injection of saline as a negative control. Wild-type mice 3 days after laser treatment displayed: (i) disruption of the RPE and outer nuclear layer, (ii) proliferation of RPE cells, and (iii) breakdown of the blood retinal barrier. Our data consistently indicated that IFN-γ increased retinal damage following laser treatment. In the presence of excess IFN-γ, laser treated mice displayed (as compared with saline injected controls): (i) increased thickening of the inner nuclear layer, (ii) increased infiltration of inflammatory cells, (iii) increased fluorescein leakage, (iv) increased activation of Muller cells, (iv) increased activation and migration of microglia, and (v) a significant increase in retinal damage as indicated by a depression of b-wave amplitude. By contrast, in the absence of IFN-γ, laser treated IFN-γ KO mice displayed (as compared with wild-type mice): (i) reduced fluorescein leakage, (ii) reduced infiltration of inflammatory cells, (iii) reduced activation of Muller cells, and (iv) reduced retinal damage as observed by the b-wave amplitude.
Conclusions::
IFN-γ increased retinal destruction and gliosis following laser burns. Our data indicate that the primary retinal damage induced by the laser burn is increased in the days following the injury by infiltrating inflammatory cells. Therefore, if inflammation is quickly controlled, secondary retinal damage will be minimized.
Keywords: inflammation • wound healing • microglia