In this context, the investigation of immune checkpoint inhibitors, particularly programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), has gained prominence in recent years, as these molecules have been linked to immunosuppression, disease progression, and a poor prognosis (8, 9), including in bovine infectious diseases (10–12). Here, PDCD1 is linked to infectious disease.