Objective To investigate the expression of programmed cell death receptor-1 (PD-1)/programmed cell death ligand 1 (PD-L1) in patients with primary immune thrombocytopenia (ITP) and the interaction between regulatory T cells (Treg) and regulatory B cells (Breg). Methods 106 ITP patients treated in our hospital from December 2018 to January 2022 were selected as the observation group, including 32 mild patients, 44 moderate patients and 30 severe patients. At the same time, 100 healthy volunteers were selected as the control group, and the Treg cells, Breg cells, the positive rate of PD-1 on the surface of Treg cells, and the positive rate of PD-L1 on the surface of Breg cells and so on were detected in the two groups. At the same time, the differences of various indicators in patients with different disease severity in the observation group were analyzed. Results Breg cells, Treg cells, transforming growth factor-β (TGF-β), interleukin-10 (IL-10) and interleukin-4 (IL-4) in the observation group were (4.51±1.02)%, (5.02±1.00)%, (2156.65±354.43) pg/ml, (4.10±0.99) pg/ml and (301.12±65.56) pg/ml, respectively, which were significantly lower than those in the control group (P<0.05). The positive rates of PD-1 on the surface of Treg cells, PD-L1 on the surface of Breg cells, soluble programmed cell death protein-1 (sPD-1) and interleukin-17 (IL-17) in the observation group were (28.34±9.22)%, (12.19±2.11)%, (102.87±15.56) pg/ml and (11.45±2.32) pg/ml, respectively, which were significantly higher than those in the control group (P<0.05). There was no significant difference in soluble programmed cell death protein ligand 1 (sPD-L1) between the observation group and the control group (P>0.05). The Breg cells and Treg cells of the severe patients in the observation group were (3.52±0.94) % and (3.80±1.02) %, respectively, which were significantly lower than those of the mild and moderate patients (P<0.05). The positive rates of PD-1 on Treg cells and PD-L1 on Breg cells were (32.53±7.04) % and (14.14±2.01) %, respectively, which were significantly higher than those of mild and moderate patients (P<0.05). The positive rate of PD-1 on Treg cells was positively correlated with the positive rate of PD-L1 on Breg cells (r=0.466, P<0.05). After treatment in the observation group, Breg cells, Treg cells, TGF-β, IL-10 and IL-4 were increased (P<0.05), while the positive rate of PD-1 on Treg cells, PD-L1 on Breg cells, sPD-1 and IL-17 were decreased (P<0.05), there was no significant difference in sPD-L1 before and after treatment (P>0.05). Conclusion The positive rates of PD-1 on the surface of Treg cells and PD-L1 on the surface of Breg cells in patients with ITP are significantly increase, which is positively related to the severity of the patient's condition, and there is a correlation between the expressions of PD-1 on the surface of Treg cells and PD-L1 on the surface of Breg cells, which is worthy of further study