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Natural killer and natural killer T-like cells in bronchoalveolar lavage fluid and peripheral blood in diffuse lung diseases

Introduction: Natural Killer (NK) and NK T-like (NKT) cells have immune regulatory functions that might be involved in the modulation of bronchoalveolar inflammation in diffuse lung diseases (DLD). Aim: Analysis of frequency of NK and NKT cells in bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) of patients with different types of DLD. Methods: Included 202 patients, 106 with sarcoidosis, 53 hypersensitivity pneumonitis (HP) and 43 with other DLD. BALF and PB lymphocyte subpopulations were studied by flow cytometry. NK cells (CD3-CD16/56+) and NKT cells (CD3+CD16/56+) were scored in percentages of lymphocytes. Results: Patients had a mean (SD) age of 46.8(15.8) years, 41.6% male. The relative number (%) of NK cells were significantly lower in BALF than PB ( p p p =0.027). There were no differences regarding BALF NKT/NK ratio. In PB, no differences within groups were found regarding %NK cells, but %NKT cells were higher in sarcoidosis patients ( p =0.01). Also in sarcoidosis, a negative correlation was found between BALF CD4/CD8 ratio and NKT/NK ratio ( r =-0.209, p =0.04). Conclusions: Higher BALF NK and NKT cells were found in HP, consistent with previous studies. In sarcoidosis, higher circulatory NKT cells but not in BALF were identified. This finding, together with BALF negative correlation of CD4/CD8 and NKT/NK, leads us to hypothesise that a relative depletion of NKT cells could promote, through the lack of immunoregulatory effect, the characteristic local TCD4+ cell proliferation of sarcoidosis.