Lower expression of PD-1 and PD-L1 in peripheral blood from patients with chronic ITP.

Background: T-cell dysregulation is a major event involved in immune thrombocytopenic purpura (ITP). Increasing data have indicated that abnormal expression of T-cell immunosuppressive receptors, such as programmed death (PD) 1 and cytotoxic T lymphocyte antigen-4 (CTLA-4), may be related to autoimmune disease pathogenesis. Methods: We analyzed the expression levels of PD-1, its ligand PD-L1, and CTLA-4 in peripheral blood mononuclear cells from 18 patients with chronic ITP by real-time polymerase chain reaction, and samples from 20 healthy individuals served as control. Results: The results demonstrated significantly lower expression of PD-1 (median: 0.0015) and PD-L1 (median: 0.0572) in chronic ITP patients compared with healthy individuals (PD-1: median: 0.0117, P < 0.0001; PD-L1: median: 0.5428, P < 0.0001), while there was no significant difference in the CTLA-4 expression level between the chronic ITP patients (median: 0.0818) and healthy individuals (median: 0.1667) ( P = 0.219). Moreover, a positive correlation between the expression levels of PD-1 and PD-L1 (r(s) = 0.486, P = 0.041) and CTLA-4 and PD-1 (r(s) = 0.643, P = 0.004) in the chronic ITP patients was found. Conclusion: Consistently lower expression of T-cell immunosuppressive receptors is a common characteristic of chronic ITP, which may be associated with its pathogenesis.