Abstract
Purpose: :
Prior studies demonstrated that sera of glaucoma patients show autoantibodies against myelin basic protein (MBP) and complex antibody profiles against human optic nerve antigens. Aim of this study was to examine if immunization with MBP or optic nerve homogenate (ONH) causes retinal ganglion cell (RGC) loss in an experimental autoimmune glaucoma animal model and to determine time and antigen dependency of possible RGC loss.
Methods: :
Rats (n=11 per group) were immunized with 1mg MBP, 8mg bovine ONH or 8mg keratin, a non-eye-related antigen, plus Freund’s adjuvant and pertussis toxin. A control group received only Freund’s adjuvant and pertussis. Half-dose booster immunizations were conducted after 4 and 8 weeks. In order to detect RGC loss, retinal flatmounts were stained with cresyl 2, 4, and 10 weeks after immunization. RGC nuclei were counted manually in 8 predefined areas. Intraocular pressure (IOP) was measured by applanation tonometry and funduscopies were performed regularly throughout the study. All data were analyzed using ANOVA and post hoc test.
Results: :
Animals immunized with MBP and ONH showed significant RGC loss in comparison to controls at all time points (P<0.02). Most severe RGC loss occurred within the first two weeks (14%). RGC loss was moderate between 2 and 4 weeks (6% from week 2 to week 4). At 10 weeks, with two booster immunizations, a continuous loss of 3% per week from week 4 to week 10 occurred. No significant difference in cell counts of animals immunized with keratin in comparison to controls could be observed (P=0.80). RGC loss in the control groups of all studies never exceeded 2% per week. Mean IOP was between 12 and 13 mmHg for all groups at all times with a standard deviation between 2.5 and 2.8 mmHg. IOP neither changed over time nor showed significant difference between groups (P>0.9) and funduscopy revealed no abnormalities.
Conclusions: :
Immunization with MBP or ONH lead to significant RGC loss after 2, 4, and 10 weeks. The non-eye-related antigen keratin caused no RGC loss, thus proving that RGC loss is specific for certain antigens. In this model RGC loss was not caused by an increase in IOP, which makes it suitable to investigate the autoimmune component in the pathogenesis glaucoma. Our model might reflect the clinical observation in glaucoma patients with changed antibody patterns and could therefore lead to new therapeutic strategies.
Keywords: ganglion cells • pathology: experimental • intraocular pressure