Background: Diffuse lung diseases (DLD) are characterized by different immunophenotypes in the bronchoalveolar\nlavage fluid (BALF). We aimed to evaluate the diagnostic value of BALF NK and NKT cell counts of patients with\nDLD and lymphocytic alveolitis.\nMethods: We assessed 202 patients with DLD, who underwent BALF immunophenotyping. Samples were routinely\nprocessed by flow cytometry and lymphocyte subsets were compared between patients with sarcoidosis (n = 106),\nhypersensitivity pneumonitis (HP; n = 53), and other DLDs (n = 43). We compared absolute counts and percentages\nof NK and NKT cells between patients with HP versus the remaining DLD patients. To assess the accuracy of BALF\nlymphocyte subsets in the diagnosis of HP, we calculated the respective areas under the receiver operating\ncharacteristic curves (AUC-ROC).\nResults: Patients with HP had significantly higher numbers of BALF NK cells, and its percentage was significantly\nassociated with a higher odds of HP, even after adjustment for the NKT and CD8+ cells. For the absolute number\nof BALF NK cells, we found an AUC-ROC of 0.76 (95%CI = 0.68â??0.84) when comparing patients with HP versus the\nremaining DLD. The cut-offs of 2000 NK cells/mL and of 2.4% NK cells in the BALF had a specificity and a negative\npredictive value over 80% for the diagnosis of HP. BALF NK cells absolute counts were significantly higher in HP patients\nwith a restrictive pattern. No such differences were observed for NKT cells.\nConclusions: BALF NK immunophenotyping may be a helpful adjunct to the diagnostic work-up of DLD, particularly in\nthe differential diagnosis of HP.
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