WASHINGTON: Scientists at Ohio State University have discovered an association between increased levels of two immune system proteins that are essential for inflammation and a latent viral infection, besides suggesting a chain of events that might accelerate cardiovascular disease.

The researchers say that the same process may be behind a number of other illnesses that afflict the elderly. Apart from this, the study also implicates chronic depression in the production of plaques that clog coronary arteries, they add.

"To me, this suggests a new way of thinking about how these diseases develop. We carry around these latent herpes viruses in our bodies virtually all our lives and periodically they can hurt us, inducing biological events that could lead to an increased risk of atherosclerosis," said Ronald Glaser, a professor of molecular virology, immunology and medical genetics at Ohio State University.

He revealed that for years, he had studied Epstein-Barr virus (EBV), one of eight different herpes viruses that can remain dormant in the body for a lifetime.

"Perhaps more than 90 per cent of the people in North America have been infected by EBV by the time they're adults. Virtually everybody in the country is carrying this virus," he said.

During the course of study, the researchers initially focused on the role that two essential proteins -- interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-a) -- play in producing inflammation, a major part of the body's immune response.

They say that the levels of IL-6 increase in the blood as the immune system ages, and that some of IL-6 in the body is also created by immune cells called macrophages that rush to the site of an infection or injury.

In their previous study, the researchers had found that increases in psychological stress and depression could substantially raise the levels of IL-6 and TNF-a in the body. They also had evidence that as Epstein-Barr virus begins to multiply in cells in the body, it produces a protein called dUTpase that can further stimulate macrophages to make even more IL-6.

"The more IL-6 levels rise in the body, the greater a person's risk is for disease," Glaser said, adding that increase IL-6 increases and depression are associated with cardiovascular disease, osteoporosis and type-2 diabetes.

When the researchers exposed endothelial cells and the immune macrophages to Epstein-Barr virus and the dUTpase protein, the production of IL-6 and TNF-a proteins was increased.

"Basically, we're seeing all of these factors as playing a significant role in the production of these pro-inflammatory proteins. We were very surprised to find all these connections. They weren't expected. This may help us understand just how atherosclerotic disease may occur, or how it is exacerbated by many factors," said James Waldman, an associate professor of pathology.

"People need to remember how important depression is and that when they're depressed, it can reactivate these viruses, starting the cascade that leads to inflammation, perhaps increasing the risk of cardiovascular disease. So treating depression is very important," Glaser added.

The study has been published in the journal Brain, Behaviour and Immunity.