Joslin researchers have identified immune cells that promote growth of beta cells in type 1 diabetes. This study provides further evidence of a changed role for immune cells in type 1 diabetes pathology. The study appears online today and will also appear in the January issue of Diabetes.
In type 1 diabetes, the immune system infiltrates pancreatic islets and destroys insulin-producing beta cells. However, previous studies in non-obese diabetic (NOD) mice have suggested that immune cells can also contribute to preserving beta cells. This notion is strengthened by the observation by Joslin researchers who reported that members of the Center's 50-Year Medalist Study, who have lived with type 1 diabetes for 50 years or more, retain some beta cells and produce insulin.
"The traditional view of type 1 diabetes was that immune cells killed all beta cells and people with the disease would have to take insulin for life. But we know that some beta cells do survive and secrete insulin even when the patients have had type 1 diabetes for 50 years," says senior author Rohit N. Kulkarni, M.D., Ph.D., a Senior Investigator in the Section on Islet Cell and Regenerative Biology at Joslin and Associate Professor of Medicine at Harvard Medical School.
In this study, Joslin researchers were interested in learning exactly how immune cells could promote beta cell growth and identifying the type of cell and the mechanisms underlying this effect.
In a series of experiments, the researchers injected NOD mice with immune cells from the pancreatic islets of donor NOD mice and assessed their effects on beta cells. The immune cells tested included subtypes of B or T immune cells.
The researchers found that it is T cells not B cells that are associated with beta cell proliferation. Mice that received B cells showed no difference in beta cell growth. Mice that received the T cell subtypes CD4+ and CD8+ showed an elevation in all markers of beta cell proliferation compared to mice that did not receive them. The researchers also found that beta cell growth happens after islets are infiltrated by immune cells and is independent of the effects of glucose and insulin.