Immune Cells in Retina Can Regenerate

Images of mouse retina after being treated with a drug that nearly eliminates immune cells called microglia. On day 0 when the drug was stopped, nearly all microglia are gone; 7 days later, microglia have migrated across the retina, and by day 10 they have increased in number.

Photo:  Wai T. Wong/NEI

Immune cells called microglia can completely repopulate themselves in the retina after being nearly eliminated, according to a new study in mice from scientists at NEI. The cells also re-establish their normal organization and function.

The findings point to potential therapies for controlling inflammation and slowing progression of rare retinal diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), the most common cause of blindness among Americans 50 and older. A report on the study was published online Mar. 21 in Science Advances.

“Neuroinflammation is an important driver of the death of neurons in retinal diseases,” said the study’s lead investigator Dr. Wai Wong of NEI. “Our study is foundational for understanding ways to control the immune system in the retina.”

Control of the immune system is important for developing new treatments for a variety of eye conditions, including AMD, RP or for certain types of retinal injury.

The retina is a thin layer of cells in the back of the eye that includes light-sensing photoreceptor cells and other neurons involved in transmitting visual information to the brain. Mixed in with these cells are microglia, specialized immune cells that help maintain the health of the retina and the function of retinal neurons.

Microglia are also present in other parts of the central nervous system, including the brain. In a healthy retina, communication between neurons and microglia is important for maintaining the neuron’s ability to send signals to the brain.

When the retina is injured, however, microglia have an additional role: They migrate quickly to the injury site to remove unhealthy or dying cells. However, they can also remove healthy cells, contributing to vision loss.

Studies show that in degenerative retinal disorders such as AMD and RP, inhibiting or removing microglia can help retain photoreceptors and thus slow vision loss. But return of microglia is still important to support the retina’s neurons.