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A research team from Massachusetts Eye and Ear and the Massachusetts Institute of Technology has shown that immune cells in the eye that developed in response to early exposure to bacteria are a key contributor to progressive vision loss from glaucoma. High pressure in the eye leads to vision loss by setting into motion an autoimmune response that attacks the neurons in the eye similar to immune responses triggered by bacterial infections.
Current glaucoma therapies are designed to lower eye pressure; however, patients with glaucoma are treated and their eye pressure returns to normal, they can still have vision loss. Stress from high eye pressure can initiate an immune response that triggers T cells to attack neurons in the eye. Glaucoma is a group of eye conditions that often culminate in irreparable damage to the optic nerve, which transmits visual information from the eye to the brain.
Elevated eye pressure is the most important risk factor for glaucoma. When pressure in the eye rises, it induces the expression of heat shock protein, a family of proteins that develop in response to stressful conditions. This leads to a response from immune cells-memory T cells that are programmed to respond to heat shock proteins.
The memory T cells attack the neurons of the retina, leading to degeneration of the optic nerve and often permanent loss of vision. T cell responses are essential in the development of progressive vision loss following elevated eye pressure. The research team observed an immune response to heat shock proteins both in mice and in human patients with glaucoma.
The team detected T cells in the retina of a mouse model of glaucoma, which motivated experiments to determine if the T cells played a role in neuron loss. The team studied three groups of mice with glaucoma-some without T cells, some without B cells, and some without T or B cells.
Overwhelmingly, they observed a loss of neurons in the mice only if the mice contained functional T cells. More strikingly, development of glaucoma-inducing T cells required early exposure to bacteria; mice never exposed to bacteria (being raised in a “germ-free” facility) were free from glaucoma under elevated eye pressure.
The researchers also studied blood samples from patients with primary open angle glaucoma (POAG), the most common type of glaucoma. In humans, they observed T cells responses similar to the mice that were well over 5-fold higher in patients with POAG compared to samples from patients without POAG.