gms | German Medical Science

Background: Laser-induced choroidal neovascularisation (CNV) is a commonly used animal model to investigate pathological processes that occur during wet age-related macular degeneration (AMD) and to test potential measures against neovascularisation. Microglial cells are the intrinsic immune cells of the central nervous system and also of the retina. Involvement of microglial cells in the pathology of AMD is of increasing interest. We therefore checked the behaviour of microglial cells in the laser-induced CNV with respect to the expression of various neurotrophic factors and cytokines.

Methods: Eyes of adult wild-type mice were treated by an argon laser (200 mW, spot diameter 75 µm) to induce CNV. After four days or one week, eyes were isolated. Cryosections were prepared for immunohistochemistry by standard protocols. Microglial cells were stained using CD11b and F4/80 antibodies. Double staining of microglial cells was performed against VEGF, FGF-1, PDGF-beta, TGF-beta1, PEDF, TNF-alpha, the interleukines-1beta, -6, -8 and -17, MMP-9 and MKi67.

Results: Numerous microglial cells were detected in the region of the laser spot. A subpopulation of microglial cells showed immunoreactivity (IR) for the growth factors VEGF, PDGF-beta and FGF-1 as well as for the typical pro-inflammatory factors TNF-alpha and IL-6. No IR was observed for PEDF and TGF-beta1 as well as for IL-1beta, IL-8, IL-17, MMP-9 and MKi67. Notably, there were slight differences in co-localisation behaviour depending on whether microglial cells were labelled by CD11b or F4/80. Moreover, we found differences in the intensity of immunoreactivity depending on the time point of eye isolation. As an example, IR for IL-6 was higher one week after laser treatment.

Conclusion: Microglial cells are present at a high number at the sites of lesion in the model of laser-induced CNV. They express a limited number of growth factors and cytokines. Lack of MKi67 IR indicates a low level of proliferation, leading to the conclusion that at least most of microglial cells were migrating into the laser spot. Further investigation will deal with possible subpopulations of retinal microglia, and we will check expression pattern of the microglia at other time points after laser injury.