Suspected cause of type 1 diabetes caught 'red-handed' for the ...(une system reaction. The lymphocytes lea...),Health

Date:5/9/2008

une system reaction. The lymphocytes lead immune attacks against foreign invaders like bacteria and viruses and eliminate them, clearing infections. But when interaction between an antigen-presenting cell and a lymphocyte leads to a part of the body being mistakenly identified as alien, the resulting attack harms the body, causing autoimmune diseases.

Although dendritic cells' presence in the islets and their ability to summon immune attacks made them likely suspects in type 1 diabetes, they were challenging to isolate from the pancreas for closer examination.

"They're very tiny and there are only about 5 to 10 of them per islet, each of which contains approximately a thousand cells," explains Unanue. "So the senior postdoctoral researcher in the lab who did this work, Boris Calderon, had to develop some sophisticated cellular assays to pick them up."

Calderon, M.D., found indications that the cells were carrying granules of insulin and pieces of proteins from beta cells on their cell surfaces. To test whether this cargo carried by the dendritic cells had the potential to trigger an immune attack on beta cells, Calderon exposed the dendritic cells to lymphocytes taken from diabetic mice. The lymphocytes were activated by the dendritic cells of the islets and switched into attack mode.

In a separate line of research, Unanue's lab has learned that dendritic cells in the pancreas may normally have beneficial effects on the health of beta cells. They've shown that when dendritic cells are absent from the pancreas, the beta cells are smaller, an indication that they're not as healthy.

"We think these dendritic cells aren't in the pancreas by accident," says Unanue. "We believe that in the normal individual they help maintain the health of beta cells. But in a person with autoimmune diabetes, they appear to start the problems that destroy beta cells."

The key distinction likely lies in a group of proteins called
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Contact: Michael Purdy purdym@wustl.edu 314-286-0122 Washington University School of Medicine Source:Eurekalert

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