PDCD1 and systemic lupus erythematosus: After the stimulation with IL-2 for 48 hours, the ability of B-cells in SLE patients to up-regulate PD-L1 expression is significantly reduced (50).In the serum of SLE patients, although the number of B cells is significantly expanding and the transcription level is increasing, the effector molecules connecting B cells and PD-1 are phosphorylated by tyrosine kinase and PD-1 cannot be effectively expressed.