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 CD56bright and CD56dim NK cells in LTBI patients was higher than that of APTB patients, but the frequency of HLA-DR+ CD56bright NK cells was significantly lower than that of HCs and APTB patients. Also, LTBI patients with CD56bright 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+ NK cells, CXCR3+ CD56bright and CXCR3+ CD56dim NK cells were significantly lower in LTBI patients.

Conclusions: Circulating CD56bright NK cells exerted a significant role in maintaining immune balance in LTBI patients. An elevated frequency of granzyme B+ CD56bright NK cells and a reduced frequency of perforin+ CD56bright NK cells were effective in differentiating LTBI patients from HCs.