PDCD1 and type 1 diabetes mellitus: There was a statistically significant increase in PD1 expression in the T1D patient group, compared to the control group, in central memory CD4+ T cells (5.45 ± 3.67 vs. 2.35 ± 1.68 cells/μL), effector memory (159.4 ± 82.63 vs. 101.8 ± 68.54 cells/μL), and effector (2.19 ± 2.89 vs. 0.5141 ± 0.6044 cells/μL).