Changes in immune status of circulating NK cells in patients with latent tuberculosis infection

Introduction The presence of patients with latent tuberculosis infection (LTBI) has fueled the tuberculosis pandemic. We aimed to investigate the immune status of NK cells in LTBI patients. Material and methods Twenty-one LTBI patients, 25 active pulmonary tuberculosis (APTB) patients and 25 healthy controls (HCs) participated in our research. The markers of NK cells were detected by flow cytometry. Results The absolute number of circulating CD56<sup>bright</sup> and CD56<sup>dim</sup> NK cells in LTBI patients was higher than that of APTB patients, but the frequency of HLA-DR<sup>+</sup> CD56<sup>bright</sup> NK cells was significantly lower than that of HCs and APTB patients. Also, LTBI patients with CD56<sup>bright</sup> NK cells had intracellular levels of granzyme B that were as significantly elevated as those with APTB patients, but the levels of granzyme A and perforin were reduced. Meanwhile, the frequencies of CXCR3<sup>+</sup> NK cells, CXCR3<sup>+</sup> CD56<sup>bright</sup> and CXCR3<sup>+</sup> CD56<sup>dim</sup> NK cells were significantly lower in LTBI patients. Conclusions Circulating CD56<sup>bright</sup> NK cells exerted a significant role in maintaining immune balance in LTBI patients. An elevated frequency of granzyme B<sup>+</sup> CD56<sup>bright</sup> NK cells and a reduced frequency of perforin<sup>+</sup> CD56<sup>bright</sup> NK cells were effective in differentiating LTBI patients from HCs.