Immune cells in the retina can spontaneously regenerate

Immune cells in the retina can spontaneously regenerate

Immune cells called microglia can completely repopulate themselves in the retina after being nearly eliminated, according to a new study in mice. 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 in Science Advances.

"Neuroinflammation is an important driver of the death of neurons in retinal diseases," said the study's lead investigator. "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.



Researchers were interested in understanding what happens in the retina after microglia have been eliminated, particularly whether the cells could return to their normal arrangement and fulfill their normal functions. To test this, they depleted the microglia in the retinas of mice using the drug PLX5622 (Plexxikon), which blocks the microglial CSF-1 receptor. Microglia depend on continuous signals through this receptor for survival. Interruption of this signaling for several days caused the microglia to nearly disappear, leaving just a few cells clustered around the optic nerve--the cable-like bundle of nerve fibers that carries signals from the retina to the brain--in the mouse retinas. Since loss of microglia for a short time doesn't affect the function of neurons, removing microglia temporarily--in order to reduce inflammation for example--could potentially be useful as a therapeutic intervention for degenerative or inflammatory disorders of the retina.

"If we were to get rid of the microglia while a large, inappropriate immune response was happening," said the author, "we might be able to miss the worst of the inflammation, but still come back into balance at a later point in time. We could hit pause on the immune system in the retina in a directed way."


"The organization of these immune cells is quite elaborate, and all the organization comes right back," author said. "We can actually image the eye and watch these cells divide and split and migrate as part of the repopulation response."


