Mayberry, Jordan1; Zeng, Huilan1; Kuehn, Markus H.1,2
1Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, IA; 2VA Center for the Prevention and Treatment of Visual Loss, Iowa City, IA
Purpose: Loss of retinal ganglion cells (RGC) is the ultimate cause of vision loss in glaucoma. Although elevated intraocular pressure (IOP) has been identified as a main risk factor for the development of glaucoma, disease progression is likely due to multiple pathomechanisms. Previous studies in our laboratory have demonstrated that adoptive transfer of CD3+ cells from glaucomatous mice into healthy recipients results in progressive loss of RGC. Conversely, RAG mice lacking T or B cells, are profoundly protected from glaucomatous damage caused by elevated IOP. These findings indicate that adaptive immune responses are one of the factors leading to vision loss in glaucoma. The current study was carried out in order to determine the functional contribution of CD4+ and CD8+ T cells in this process.
Methods: Elevated IOP was induced in the eyes of C57Bl/6J controls, Cd4 knockout (KO), and Cd8 KO mice through intracameral injection of Ad5.MyocY437H (n=25/group). IOP was measured weekly using rebound tonometry. Visual function was determined every month by measurements of the optokinetic response (OKR). RGC loss was assessed in whole-mounted retinas following immunohistochemical labeling of RGC with antibodies directed against RBPMS. After 4 months of elevated IOP, spleens were harvested, homogenized, and transferred into RAG recipient mice by intraperitoneal injection.
Results: After 4 months of elevated IOP, the OKR in controls had decreased by 0.097 cycle/degree (c/d), whereas visual acuity in Cd4 KO decreased by 0.050 (p=0.03) and by 0.068 c/d in Cd8 KO (p=0.26). RGC density decreased in all groups with elevated IOP (p<0.0009). Losses in neither Cd4 nor Cd8 KO were significant when compared to control mice. RAG mice receiving adoptive transfers of splenocyte preparations from these groups also developed RGC damage. 4 months after transplantation, OKR responses in RAG which had received control splenocytes decreased by 0.069 c/d (p=0.032), whereas those that received Cd4 KO or Cd8 ko splenocytes decreased by 0.048 c/d (p=0.21), or 0.083 (p=0.009), respectively. RGC density in recipient mice decreased from 3,404 cells/mm2 in naïve RAG mice to 2,865 cells/mm2 in control recipients, 2,938 cells/mm2 in Cd4 KO recipients, and 2,544 cells/mm2 in Cd8 KO recipients. No differences between Cd4 or Cd8 KO were found when compared to control recipients.
Conclusions: Neither absence of CD4+ or CD8+ cells resulted in robust RGC protection in donor or recipient mice. This suggests either compensatory mechanisms in Cd4 and Cd8 KO mice, or that other splenocyte cell populations contribute stronger to RGC loss than appreciated.
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