PDCD1 and type 1 diabetes mellitus: However, a Japanese study that compares PD-1 expression in peripheral CD4+ T cells between type 1A diabetes (classical type 1 diabetes), FT1D, and healthy controls found that there is no difference between FT1D and healthy controls in PD-1 expression and that there is lower PD-1 expression in CD4+ T cells in patients with type 1A diabetes [41].