Each member of herpes virus family is contagious, incurable, and easily transmitted between people. Sinisterly, they can even evade the immune system by hiding quietly within nerve cells (neurons). Now, a new study published in the journal mBio reveals that more than just concealing themselves, some herpes viruses may productively infect, and perhaps consequently damage these nerve cells.
Epstein-Barr virus (EBV) is one of the most common to infect humans, transmittable through saliva and genital secretions. Researchers at the Perelman School of Medicine at the University of Pennsylvania have now uncovered a new ability of this virus, and another member of the herpes family, Kaposi’s sarcoma-associated herpesvirus (KSHV).
Medical researchers have long known that in patients with Alzheimer’s disease, multiple sclerosis, and several other related neurological diseases, their cerebrospinal fluid – the solution that acts as a protective buffer for the brain inside the skull – is loaded with EBV particles.
The team from Pennsylvania also noted that those who previously suffered from “mono,” or glandular fever, caused by EBV, have been found to be more likely to develop multiple sclerosis in later life. In addition, the drug acyclovir – which is able to inhibit the action of EBV – has been shown to have an (albeit limited) effect on reducing the symptoms of multiple sclerosis. Taken together, these suggested the presence of a link between the virus and these conditions, which the team decided to examine further.
Image credit: The herpes virus comes in eight different forms. Creations/Shutterstock
Firstly, modified versions of EBV and KSHV were made by inserting a gene that produces a green fluorescent protein. Several human neuron types were then infected with these modified viruses, including neuroblastoma (cancerous nervous system cells), and fetal neural cells. The green “glow” allowed the researchers to track the progression of the virus though the neurons.
Regardless of whether EBV or KSHV was used, the fluorescent signal was detected within the neural cells, indicating that the virus had infiltrated their interior. Key proteins produced by the virus as it begins to hijack the host cell's programming and replicate its genetic material were also observed. Chillingly, the infected cells also contained functional viral particles that would be capable of infecting other cells, meaning that the infection at some point likely involves the bursting open (lysing) of the neural cells.
“I couldn't believe it,” Erle Robertson, a professor of Microbiology at the Abramson Cancer Center and one of the authors of the study, said in a statement. “After 50 years of studying EBV, nobody had ever seen the virus in nerve cells. But maybe they just never looked.”
Interestingly, when these viruses infect other cell types, such as B cells (a type of white blood cell), they enter a latent mode and remain dormant for long periods of time. This is quite strikingly contrasted with the highly destructive method of infection seen when they infect neural cells.
While this study indicates that members of the herpes family of viruses can infect neural cells, it does not directly show that they cause neurological conditions like Alzheimer’s or multiple sclerosis. Only time will tell if this is also shown to be the case.