Exploring the role of programmed cell death protein 1 and its ligand 1 in eye diseases.

Programmed death receptor-1 (PD-1) and its ligand, PD-L1, as negative co-stimulatory molecules, are indispensable for regulating both physiological and pathological immune responses. The PD-1/PD-L1-mediated signaling pathway has been studied extensively in cancer research and has become a hotspot for biopharmaceuticals and immunotherapy. Furthermore, monoclonal antibodies to PD-1 have just been approved by the US Food and Drug Administration to treat certain types of malignancies. Recent research has unveiled a close association between the PD-1/PD-L1 system and eye diseases. This review describes the expression and physiological functions of PD-1 and its ligand in ocular tissues and summarizes the pathogenic, regulatory, and therapeutic roles of PD-1/PD-L1 system in eye diseases, including uveal melanoma, autoimmune uveitis, autoimmune dry eye, sympathetic ophthalmia, Graves' ophthalmopathy, diabetic retinopathy, herpes simplex keratitis, and trachoma, with the intent of highlighting the potential of PD-1/PD-L1 as novel therapeutic targets or biomarkers for these ocular diseases.