Attenuation of lymphocyte immune responses during Mycobacterium avium complex-induced lung disease due to increasing expression of programmed death-1 on lymphocytes.

Mycobacterium avium complex-induced lung disease (MAC-LD) becomes important due to its increasing prevalence. Attenuated cellular immunity associated with programmed cell death (PD)-1 may play a pathophysiological role in MAC-LD but lacks of investigation. We enrolled 80 participants in this prospective study, including 50 with MAC-LD and 30 healthy controls. Peripheral blood mononuclear cells (PBMCs), lymphocytes and monocyte-derived macrophages were used for MAC antigen stimulation. Patients with MAC-LD had lower tumor necrosis factor-α and interferon-γ responses compared to the healthy controls in PBMC stimulation assays with MAC bacilli. These responses improved after MAC treatment. The PD-1 and PD ligand expressions and apoptosis were higher in the lymphocytes of the patients with MAC-LD compared to the controls. Both PD-1 and apoptosis on T lymphocytes were significantly increased in the patients with MAC-LD, either by direct MAC stimulation or by MAC-primed macrophage activation. Partially blocking PD-1 and the PD ligand with antagonizing antibodies in the stimulation assay significantly increased the cytokine production of IFN-γ and decreased the apoptosis on T lymphocytes. In conclusion, the patients with MAC-LD have attenuated lymphocyte immunity, which might be associated with increasing activation of PD-1 and PD-1 ligand. Regulating such activation might improve the lymphocytic secretion of IFN-γ and reduce apoptosis.