Neutrophil predominance in bronchoalveolar lavage fluid is associated with disease severity and progression of HRCT findings in pulmonary Mycobacterium avium infection

Pulmonary Mycobacterium avium complex (MAC) infection is increasing in prevalence worldwide even in immunocompetent individuals. Despite its variable clinical course, the clinical and immunological factors associated with radiographical severity and progression are not largely unknown. We aimed to study the association between the inflammatory cell and cytokine profiles at the local infected site, and the radiological severity and/or progression of pulmonary MAC infection. In this retrospective cohort study, 22 healthy subjects and 37 consecutive patients who were diagnosed as having pulmonary MAC infection by positive cultures of bronchoalveolar lavage (BAL) fluids were enrolled. The 37 patients were divided into 2 groups based on the predominant BAL inflammatory cell type: the lymphocyte-dominant (LD) group and neutrophil-dominant (ND) groups. The high-resolution computed tomography score in both the lavaged segment and whole lung and cytokines profiles were compared between the 2 groups. The clinical course after the BAL procedure was also compared between the 2 groups. Both the segment and whole lung scores in the ND group were significantly higher than the LD group (P < 0.001). Levels of IL-8 in the BAL fluids were significantly higher in the ND group compared to the LD group (P = 0.01). In contrast, levels of IL-22 were significantly lower in the ND group compared to the LD group (P < 0.001). The prevalence of patients who showed deterioration of the disease was significantly higher in the ND group (83.3%) than the LD group (12.5%) (P < 0.01). Neutrophil-predominant inflammatory response at the infected site is associated with the radiographical severity and progression of pulmonary MAC infection.