The current view of type T1D is that it is a T cell mediated disease in which both CD4 and CD8 lymphocytes infiltrate the pancreatic islets, destroy insulin-producing beta cells and consequently cause diabetes. In this study we aimed at investigating the presence of immune cells within non-diabetic human islets and characterize their frequency and phenotype.
Human islets were obtained from organ donors of non-diabetic individuals. A sensitive multicolor flow cytometry analysis (IsletsFACS) of single cells suspension from isolated islets was used to define the frequency and phenotype of activated and memory T cells as well as frequency of NK and B cells. Insulin and glucagon expressing cells within the islets was also assessed. Moreover CD8+ T cells were sorted and their Vβ repertoire examined. Remarkably, lymphocytes were present in all 54 human islet samples examined. Generally, the frequency of B and NK cells were low in most of the samples, consisting of less than 5% of the lymphocyte compartment. Interestingly, about 80% of the lymphocytes were CD3+ and amongst these T cells the majority were CD8+. The central memory and effector memory phenotypes dominated both the CD8+ and CD4+ T cells, suggesting a specific recruitment of T cells rather than contaminating lymphocytes.
In conclusion, we have demonstrated the presence of lymphocytes in pancreatic islets of human non-diabetic donors and the remarkable biased towards CD8+ T cell as well as their exquisite memory phenotype. To characterize the physiological interaction between immune cells and the healthy islets will be determinant to understand the disease-related characteristic of T1D.