How herpes simplex causes corneal inflammation
Herpes-related corneal inflammation with the risk of scarring in the eye is one of the extremely unpleasant complications of an infection with the virus. Normally, only the formation of the typical fever blisters is caused by the pathogen. But sometimes the virus also affects the immune system. Especially after viral infections, in which the pathogens are not removed from the body within a short time, other problems can arise as a late effect, which are only triggered by the immune system of the person affected. An example of this is chronic liver inflammation after hepatitis B. A viral infection, for example, is also suspected to be the triggering factor for multiple sclerosis, and there are similar indications that it is involved in the development of type I diabetes (juvenile diabetes).
Scientists led by Zi-Shan Zhao from Harvard Medical School (Boston/Massachusetts) describe in the February 27, 1998 issue of Science how the herpes simplex virus causes the infection-related inflammation of the cornea. Accordingly, HSV-1 apparently has components that remind the immune system very strongly of proteins that occur in the normal human cornea. This is called viral mimicry.
The researchers first searched a protein database for the virus protein that is as similar as possible to the "keratogenic peptide" (protein of the cornea). They came across a sequence of amino acids that is almost identical and is recognized by immune cells. The result: In a kind of confusion between HSV-1 and the cornea, an immune response is set in motion, which leads to inflammation.
The proof of the development of keratitis as a result of an HSV-1 infection was then provided in laboratory mice in the opposite way: Zhao and his co-authors constructed a herpes simplex 1 virus, which contains the protein with the fatal similarity to that the cornea was absent. The result, as described in the scientific paper: "Mutated HSV-1 viruses that did not contain this peptide did not initiate an autoimmune reaction." – The laboratory mice did not start to suffer from viral corneal inflammation when infected.
The comparison: While 85 percent of the laboratory mice whose cornea was infected with the more dangerous herpes virus developed an inflammation there, this was not the case with any of the animals that had the mutated pathogens dripped onto their eyes.
