The eyes have been referred to as “the window to the brain.” Yale researchers discovered that they also act as an immunological barrier, protecting the organ from viruses and even malignancies.
In a recent study, researchers discovered that immunizations put into mice’s eyes can help block the herpes virus, a common cause of brain encephalitis. To their astonishment, the vaccine triggers an immunological response via lymphatic capillaries on the optic nerve. The findings were reported in the journal Nature.
The connection between the eyes and the brain is very close, as the optic nerve directly transmits visual information from the eyes to the brain. This connection also means that pathogens capable of affecting the brain could potentially be detected through changes or abnormalities in the eyes.
These results reveal a shared lymphatic circuit able to mount a unified immune response between posterior eye and the brain, highlighting an understudied immunological feature of the eyes and opening up the potential for new therapeutic strategies in ocular and central nervous system diseases.
Eric Song
“There is a shared immune response between the brain and the eye,” said Eric Song, an associate-research scientist and resident physician at Yale School of Medicine’s Department of Immunobiology and the paper’s corresponding author. “And the eyes provide easier access for drug therapies than the brain does.”
Wanting to investigate immunological interactions between the brain and the eyes, Song’s research team discovered that the eyes have two separate lymphatic systems that regulate immune responses in the front and back of the eye. After vaccinating mice with inactivated herpes virus, the researchers discovered that lymphatic capillaries in the optic nerve sheath at the back of the eye protected them not only from active herpes infections, but also from germs and brain tumors.
Using this new biology, Song’s team is currently studying newly developed medications from his lab administered via eye injections that may help treat macular edema, or leaky blood vessels in the retina that are frequent in persons with diabetes, and glaucoma.
Furthermore, the blood-brain barrier, which ordinarily protects the brain from pathogens and other hazardous chemicals in the bloodstream, is also present in the retina. This suggests that changes in the retina may reflect abnormalities in the blood-brain barrier integrity, possibly revealing the presence of brain infections.
“These results reveal a shared lymphatic circuit able to mount a unified immune response between posterior eye and the brain, highlighting an understudied immunological feature of the eyes and opening up the potential for new therapeutic strategies in ocular and central nervous system diseases,” the authors wrote.
