The wet form of age-related macular degeneration involves an excessive growth of blood vessels behind the retina, disrupting structure to produce a progressive and presently irreversible loss of vision. Researchers here point out a role for IL-4 in this process, though the mechanisms involved are probably a fair way downstream from the causes of chronic inflammation and immune system dysfunction that spur the development of macular degeneration. Sometimes it is a possible to find a good place to sabotage the development of pathology that is distant from the root causes, but the odds are not favorable. More commonly, later stage intervention is the path to only marginally effective therapies.
Scientists have identified an unexpected player in the immune reaction gone awry that causes vision loss in patients with age-related macular degeneration (AMD). The findings suggest that an immune-stimulating protein called interleukin-4 (IL-4) and its receptor may be promising targets for new drugs to treat AMD, a common form of age-related vision loss. In patients with AMD, inflammation in the eye triggers excessive growth of new blood vessels in the center of the retina. This process damages the photoreceptors in the eye and leads to progressive vision loss.
The team measured levels of IL-4 in the eyes of 234 patients with AMD and 104 older individuals undergoing surgery for cataracts. They found that those with AMD had higher levels of IL-4 than those undergoing surgery. Next, they found that IL-4 was also elevated in mice with a condition that mimics AMD. To determine if IL-4 was helping or harming the animals, they administered them with IL-4 and found that it increased the excessive growth of blood vessels in the eye. An antibody that blocks IL-4 production reduced this blood-vessel growth. Mice with the AMD-like condition that were genetically engineered to lack IL-4 also had less blood-vessel growth.
"Our results show that IL-4 plays a crucial role in excessive blood-vessel growth by recruiting bone marrow cells that aid this growth to the lesion in the eye. These results were surprising and suggest that normally helpful immune responses can instead cause more harm,. As IL-4 plays a key disease-promoting role in AMD, it may serve as a target for new treatments to treat this condition." Normally, bone marrow cells help the body repair damaged tissues, while IL-4 helps suppress excessive blood vessel growth.