By Nancy Humphrey

Say Chlamydia pneumoniae and before you get to pneumoniae most people think of a sexually transmitted disease.

"As soon as people hear the name Chlamydia their ears shut down," said Dr. Charles W. Stratton, associate professor of Pathology. "They either don't hear or don't understand the second part - pneumoniae. They think of Chlamydia trachomatis, a common cause of sexually transmitted diseases. c is the one that's not fun to catch."

The Chlamydia pneumoniae (C. pneumoniae) organism, first described in 1988, is not the sexually-transmitted type. It is an airborne organism that you get from breathing after a person carrying the organism has coughed.

"They float around as droplet nuclei, similar to TB. People cough and up come these infectious bodies. They float around a room. You breathe. In they come and now you've got your own."

It's how they work inside the body that Stratton, Dr. William M. Mitchell, professor of Pathology, and colleagues have been looking at for the past five years.

The study of the organism has intensified as Stratton's colleagues at Vanderbilt and other medical centers around the country, including Johns Hopkins and The Mayo Clinic, look at the role of Chlamydia in diseases such as Multiple Sclerosis, Rheumatoid Arthritis, Pyoderma gangrenosum, Coronary Artery Disease and Interstitial Cystitis.

Stratton said that Chlamydia is sneaky. When viruses invade a cell, if they are active, they integrate in the human DNA and basically take over the cell.

"They tell the cell, 'Ok, today, we're going to do nothing but make viruses and the cell often dies in this process," Stratton said.Chlamydia works in a different way. First, when you breathe in Chlamydia, it can infect the ciliated cells, the cells lining the airways. Ciliated cells are like an escalator that moves mucus along. Chlamydia can paralyze the ciliated cells because it steals their energy. So the host has a nasty respiratory infection.

When you have an active infection of any kind, the body has an immune response to it. Part of the immune response is that monocytes and macrophages try to engulf the pathogen and kill it.

But they can't always kill Chlamydia. Instead, they disseminate the organism to peripheral blood mononuclear cells and the organism can silently infect other cells in the body. "With these cryptic infections, you don't have symptoms. And because Chlamydia isn't really a virus, when it's causing a cryptic infection, it's metabolizing. It's eating, drinking, singing and dancing. It's alive."

Since Chlamydia can't make its own energy, it has to steal energy from the human cell. This means the chlamydia-infected cell doesn't work well. "If Chlamydia is actively metabolizing in a cell, it's up to no good. It's stealing energy. I can't picture anything good coming from chlamydia being in a human cell."

Chlamydia also likes to infect endothelial cells, the cells that line blood vessels. When there's inflammation in the body, there often is angiogenesis, meaning new blood cells are formed. And Chlamydia is drawn to those cells. So if Chlamydia is in the peripheral blood mononuclear cells and there's an inflammation in the host's body, you're "unlucky," Stratton said. Any secondary inflammatory process could become secondarily infected by Chlamydia no matter what the source of the inflammation, Stratton said.

"Now you've got a chronic problem," Stratton said. "Now you've got a major chronic infection in the tissue, whether it's the brain (MS) or in the joints (Rheumatoid Arthritis).

"If you have inflammation, a spider bite, a viral joint infection, viral meningitis or encephalitis, it doesn't matter what it is, if a Chlamydia-infected cells happens to end up in that inflamed area, you may have just started yourself a Chlamydia farm."

Stratton said this doesn't necessarily mean that Chlamydia causes the disease, but it may play heavily into how the disease progresses. There may be many causes of MS, Rheumatoid Arthritis or other diseases in which Chlamydia is believed to play a role.

"One thought is that Chlamydia is not the cause of anything other than pneumonia but once it causes a lung infection and gets into your peripheral blood mononuclear cells, it's available to cause secondary infections in other tissues if the infected white cells happen to go to those tissues.

"It may be that MS is an infection of the brain that is caused by viruses, and most people who get that viral infection of the brain have a headache for a week, then get better. If you happen to have Chlamydia, however, you may go on and have a chronic illness.