Sarcoidosis is a systemic granulomatous and idiopathic disease mainly affects lungs and thoracic lymph nodes. No specific markers have been identified although a potential role of Natural Killer (NK) cells in its pathogenesis has been described. This study aimed to identify for the first time NK cell distribution in three anatomical compartments.

Bronchoalveolar lavage (BAL), lung lymph node (LLN) and peripheral blood (PB) were collected from patients referred to Perugia and Siena University Hospital. NK cells (CD56^dimCD16^bright) were identified in the three cellular matrices through flow cytometry.

Twenty patients (median age, interquartile range 54 (53-57) years; 70% female) were enrolled before starting pharmacological treatment. They received a diagnosis confirmation according to multidisciplinary discussion. They had radiological Scadding stage II with nodal enlargement and parenchymal disease. NK cell percentages were higher in PB than BAL and LLN (p<0.0001).

Our findings suggested an prolonged exposure to an unknown antigen that activates innate immunity through NK cells activity. In our patients a lack of NK cells in BAL and LLN hypothesized a protective role of NK in sarcoidosis patients. NK could be considered a therapeutic strategy to reduce cytokines released and inflammatory status to avoid the chronic lung damage.