Of note, the recovery of CMV- and TB-specific responses was correlated with a decrease in PD-1 expression (r = 0.83, P = .008 and r = 0.81, P = .0007, respectively).
Pulmonary tuberculosis (TB) disease is characterized by high levels of <i>Mycobacterium tuberculosis</i> (Mtb), yet the relationship between bacterial load, PD-1 expression, and Mtb-specific T cell function in human TB has not been well-defined.
PD-1 protein expression on the surface of NK cells, CD8+ and CD4+ T cells was similar in patients with active TB disease compared to controls but declined with successful TB treatment, with the greatest decline occurring on the NK cells followed by CD8+ T cells and then CD4+ T cells.
Notably, M. tuberculosis infection was associated with an elevated expression of the inhibitory programmed death-1 (PD-1) receptor on NKT cells, and blockade of PD-1 signaling enhanced the response to α-GalCer.