To Kiss or Not to Kiss

How does the body keep from spreading a cold to a loved one?

Everyone’s worst nightmare: you feel a cold coming on right before a big date. New research shows that your body is working hard, even before you catch the cold, to try to keep you from spreading those germs.

Immunologist Chris Snyder, PhD, at Jefferson has been studying cytomegalovirus (also called CMV) one of the viruses that causes mononucleosis, a.k.a. the kissing disease, for years. He recently published research exploring how the immune system reacts to viruses like CMV that infect the salivary glands in order to transmit millions of copies of themselves to another host, i.e., your date.

We talked to Dr. Snyder about his research and what it means for others. Here’s what we learned:

What do salivary glands do to protect others from infection?

One of the most surprising findings of this paper is that the salivary glands are actually doing a lot, all the time, to reduce the spread of disease.

We knew that immune cells – our body’s main defense against viruses and bacteria – rush to the scene when salivary glands become infected by a virus like CMV or Epstein Barr Virus (EBV), which both cause mono-like symptoms. But it was surprising to see immune cells in the salivary glands when the body – but not the salivary gland specifically – was infected, and even when there was no infection at all.

We knew that the immune cells called T cells would be drawn or recruited to the salivary gland after infection. In order to learn more about the signals that drew T-cells over to the glands we tried to block many different signals that usually recruit immune cells. But it was nearly impossible to keep them out, even when there was no infection!

It looks like these glands are really set up to start blocking virus transmission from the get-go.

Why was that unexpected?

There aren’t that many places in our body that are set up with the kind of defenses we saw in the salivary glands. Most places in the body are under the immune system’s surveillance, whether or not there’s an infection. After surveying a particular place in the body, immune cells tend to leave if they don’t find an infection, letting the cells in that tissue get on with their jobs.

It looks like these glands are really set up to start blocking virus transmission from the get-go.
— Chris Snyder

However, it appears that the immune system leaves many of its guards – the memory T-cells – behind in the salivary gland, whether or not there was any infection of the salivary gland itself. These memory T cells are copies of those that had recognized infectious agents elsewhere in the body and would be able to fight the same pathogen faster than the first time, if it appeared again. Perhaps because the salivary gland is such an important “port” for disease transmission, the immune system makes sure that memory T cells are permanently stationed there, like guards at the gates, to stop pathogens from leaving to spread infection.

Should we stop kissing when we get mono, flu or other viral diseases?

For the flu, you shed the most virus – and are most infectious – when you have a fever. But you may still shed virus for up to a week after the symptoms begin. For viruses like CMV and some others, you never stop being infectious. You can shed the virus through your salivary glands for years and years after your illness and then on-and-off for the rest of your life. You might have no symptoms of the disease and still spread the virus. That’s why most adults have been infected with CMV and EBV.  For a CMV infection, there really is no better or worse time to kiss. But you can take consolation in the fact that some 80-90 percent of people on the planet already carry the virus.

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Science and Technology