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Doctors have long known that diabetics are prone to getting infections, but they couldn't say with any certainty why these patients are so vulnerable to microbial invaders.

Now British researchers think they have solved the mystery. They conducted a series of lab experiments that suggest elevated levels of glucose in the bloodstream - a hallmark of diabetes - inhibit the ability of the body's immune system to detect and fight bacterial and fungal infections.

Diabetes occurs when the pancreas doesn't secrete enough insulin or the body's cells don't use insulin properly. Insulin is the hormone that clears glucose (sugar) from the blood and moves it to cells where it is used for energy. As a result, diabetics often have much higher blood levels of glucose than normal.

For their study, the research team, led by Daniel Mitchell, an associate professor and biochemist at the University of Warwick, first analyzed the similarities between the chemical structure of glucose and two other sugars called mannose and fucose.

These sugars are found on the surfaces of certain bacteria and fungi. Under normal circumstances, specialized cells of the immune system use these sugars as target sites and will latch onto them to begin their counteraction. In other words, mannose and fucose serve as red flags that give away the presence of potentially harmful microbes, alerting the immune system to get in high gear.

Using tissue samples, the researchers tried to replicate what happens when the bloodstream is flooded with too much glucose. "When we introduced increased amounts of glucose, we found that the normal binding of an immune receptor starts to fail," Dr. Mitchell said. And some immune cells begin attaching to glucose, rather than the foreign invaders.

"It really is just a case of the glucose resembling parts of the bacterial structure," he said. "You could use the analogy that the immune cells have become blind, or their ability to sense the pathogens diminishes," said Dr. Mitchell, whose study was published in the journal Immunobiology.

If additional research confirms that elevated glucose does indeed hinder the immune system, researchers may able to develop new treatments - and possibly medications - to help bolster the body's defences against infections, he said. But those developments are still a long way off.

In the meantime, the study helps drive home the message that it's important for diabetics to keep their blood glucose levels under control through lifestyle factors including a proper diet. After all, controlling blood glucose is considered to be paramount in preventing long-term complications of diabetes such as heart disease, nerve damage and kidney disease.