An Immunohistochemical Study on the Distribution and Frequency of T Regulatory Cells in Pancreatic Islets of NOD Mice During Various Stages of Spontaneous and Cyclophosphamide-Accelerated Diabetes

Abstract

To determine if there is an abrupt change in the frequency of intraislet T regulatory (Treg) cells in female nonobese diabetic (NOD) mice preceding and following spontaneous diabetes and during cyclophosphamide-accelerated disease. The frequency of intraislet CD4-positive Treg cells was analyzed between days 21 and 250, at onset, and at 1, 2, and 3 weeks of diabetes by dual-label immunohistochemistry. Tissues were also analyzed between days 0 and 14 after injection of cyclophosphamide or diluent. In the spontaneous group, intraislet Treg cells were first observed on day 30 in CD4 T cells and increased from day 45. There was no statistical difference in the frequency of Treg cells in nondiabetic NOD mice on days 45, 60, and 90. A sustained frequency at and after 1, 2, and 3 weeks of diabetes was also observed. In the cyclophosphamide group, there was a sharp decline in the frequency of Treg cells on day 4, which remained lower on day 7 but increased by days 11 and 14. During spontaneous diabetes and after onset, the frequency of intraislet CD4-positive Treg cells remains unchanged. They may possess diminished immunoregulatory function and thus unable to counteract the increasing tempo of immune-mediated beta-cell destruction.