In addition, Jurado et al. demonstrated a direct association between PD-1 and IFN-γ at the site of infection in TB patients, indicating that T cells from HR patients were systemically activated by the specific Ag, inducing IFN-γ and generating a Th1-like microenvironment that in turn led to heighten PD-1 expression. Here, PDCD1 is linked to tuberculosis.