Disruption of the balance between PD-1 and PD-L1 can lead to the occurrence of various autoimmune diseases, including type 1 diabetes mellitus (T1DM), multiple sclerosis (MS), systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA) [34]. Here, PDCD1 is linked to systemic lupus erythematosus.