A new study out of the National Eye Institute (NEI) shows that microbes on the eyes of certain mice can ward off corneal diseases. There's great hope in the eye care community that further research into this eye microbiome can help humans in the near future.
Scientists in the past assumed that the ocular surface couldn't support a microbiome because of lysozyme. Lysozyme is a powerful antibacterial enzyme that kills most microbes that land on the surface of the eyes. NEI researchers are the first in the world to prove that one strain of bacteria, namely Corynebacterium mastitidis (C. mast), can thrive on the eye's surface and instigate an immune response.
Professor Anthony St. Leger, the lead author on this study, took a culture of bacteria from the conjunctiva of various mice at NEI. He observed that many of these cultures had Staphylococci species and C. mast in them.
Next, Dr. Leger cultured C. mast with the mice's immune cells. Leger and his colleagues found that adding the immune cells created interleukin (IL-17), which is a defense signaling protein. Later on, researchers discovered that this IL-17 also produced an immune cell called gamma delta T cells and attracted anti-microbial proteins. This means that C. mast can both provoke a strong immune response and remain unaffected by it at the same time.
To try and better understand how C. mast works on the mice's eyes, Dr. Leger split the mice into two groups. The control group just had C. mast in their eyes, and the second group was given an antibiotic that killed all ocular bacteria. Researchers then injected all the mice with the harmful fungus known as Candida albicans. Within a few days, the mice that were given an antibiotic contracted a serious ocular infection. The mice with just the C. mast, however, were resistant to Candida albicans.
Up until this point, Dr. Leger believed all mice had some form of the C. mast bacterium on their eyes. However, as he continued to do research on different mice, he found that the mice housed at the Jackson Laboratory (JAX) in Maine had no C. mast on their eyes.
This observation led Dr. Leger to try and inject the C. mast strain into the JAX mice. After inoculation, Dr. Leger noticed that the JAX mice started to produce the gamma delta T cells and IL-17. Scientists also noted that all other bacterial strains injected into the JAX mice couldn't successfully colonize like C. mast.
Interestingly, the C. mast bacterium can only be transferred from mother to child or via injection. Even when researchers kept JAX mice and NEI mice in close quarters, the C. mast bacterium didn't cross over onto the eyes of JAX mice.
Leger told reporters that this discovery will revolutionize how we think of ocular health. Just like increased research into probiotics changed how we think of gut health and our over-reliance on antibiotics, Dr. Leger believes the discovery of C. mast will change how we think of the body's immune response to ocular diseases.
Anyone interested in reading this groundbreaking study should pick up the July 11th edition of Immunity. The study was published under the title "An Ocular Commensal Protects against Corneal Infection by Driving an Interleukin-17 Response from Mucosal γδ T Cells."