Background: Although an elevated intraocular pressure (IOP) is known as the main risk factor for glaucoma, many studies also showed an involvement of the immune system in this disease. In this study we investigated if a moderate increase in IOP leads to activation of the complement system.
Methods: The IOP was elevated experimentally in the left eye of rats, whereas the fellow eye served as the control. The IOP was measured at regular intervals. The number of retinal ganglion cells (RGC) was quantified via NeuN staining. To evaluate the activation of the complement system staining for C3, membrane attack complex (MAC), and mannose-binding lectin (MBL) was performed. Furthermore, we investigated possible glia activation (GFAP and vimentin) and apoptosis (Bax).
Results: A moderate elevation of the IOP was noted from day 11 after induction of ocular hypertension (OHT) until the end of the study (28 days, p = 0.0005). In the OHT-group significantly fewer RGCs (p = 0.02) were detected. Additionally, we noted significant C3 and MAC activation in the ganglion cell layer (C3, p = 0.001 and MAC, p = 0.02) as well as in the total retina (C3, p = 0.002 and MAC, p = 0.012). An activation via the lectin pathway by MBL staining could not be detected (p = 0.40). At this point in time no alterations with regard to glia cells were noted (GFAP, p = 0.97 and vimentin, p = 0.99). No apoptosis via Bax pathway could be observed (p = 0.90).
Conclusion: The results suggest that the complement system is involved in the loss of RGCs even by a moderate IOP elevation which was indicated by significantly more C3 and MAC depositions in the OHT group.