Study Shows that T Cells Often Exist in the Human Pancreas Without Causing Type 1 Diabetes

The human pancreas is dotted with cell clusters called islets where special beta cells live and make insulin to help the body regulate its blood sugar. In people with type 1 diabetes, however, the body’s T cells invade the islets of the pancreas, target a molecule called preproinsulin, and kill the beta cells, keeping the person from producing insulin and causing type 1 diabetes.

For a long time, researchers and medical professionals have believed that the existence of T cells in the pancreas was a sure sign of type 1 diabetes. However, new research appears to refute that hypothesis.

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Scientists at La Jolla Institute for Immunology (LJI) used a special staining technique to show where T cells gathered in human tissues. They were surprised to find that even healthy people had T cells in their pancreases.

“These T cells are like predators,” says LJI’s Professor Matthias von Herrath, M.D., senior author of the new study. “And we always thought that beta cells would die if the predator was there. But it turns out the T cells are already there. They just seem to be waiting for a signal to attack.”

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We’ve known for a while that T cells exist in healthy people’s bloodstreams,. However, it’s difficult to take a pancreas sample from a living person, no one knew that T cells could be lurking in pancreases without ever causing type 1 diabetes.

The new study, however, seems to suggest that having high numbers of T cells in the pancreas is merely the human default, not an indication that type 1 diabetes is imminent. It is only when the T cells come very close to the islets and invade them that diabetes occurs.

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The results of the study show that it may not actually be malfunctioning T cells that cause type 1 diabetes. Rather, it may be something happening within the pancreas that triggers these cells to attack.

Researchers believe a future type 1 diabetes therapy aiming to stop the disease at its source would need to be localized to the pancreas. In future research, they plan to look at the proteins within islets that might be attracting the T cells. There are still a lot of questions, but we seem to be one step closer to the right answer.

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