Peripheral immune cells are associated with disease severity and chronic P. aeruginosa infection in Bronchiectasis

<bold>Introduction:</bold> Bronchiectasis (BE) is characterized by alterations in the local pulmonary immune response. We aimed to explore if there are also alterations in the systemic immune cell profile and their relationship with disease severity. <bold>Methods:</bold> Clinically stable patients with BE were recruited in the Clinic Barcelona Hospital (Spain). The presence of BE was determined by computed tomography and its severity by the Bronchiectasis Severity Index (BSI) score. The immune profile in whole blood was assessed using flow cytometry analysis. <bold>Results:</bold> 59 patients with clinically stable bronchiectasis were studied: mean age was 63±9 years, 62.7% were female and 28% had chronic infection with <italic>P. aeruginosa</italic> (PA). According to their BSI score, 51.7% of the cases were mild, 32.8% moderate and 15.5% severe. The latter group presented a lower percentage of CD56brightCD16-NK cells (p=0.027), and a higher percentage of monocytes (p=0.002), T CD8+CD28- (p=0.044) and Tregs (p=0.02) in blood, compared to patients with mild or moderate BE. Patients with chronic PA infection showed a similar profile, with also activated (HLA-DR+) Th17 and effector CD4+(p=0.033 and p=0.028) T cells. <bold>Conclusions:</bold> Patients with severe BE and/or chronic PA infection showed a decrease in NK cells and an increase of monocytes, T lymphocytes with an "exhausted/activated” phenotype and an inverted Th17/Tregs ratio in peripheral blood, indicating an altered systemic immune response in these patients. <bold>Funding:</bold> Instituto de Salud Carlos III (PI21/00419), SEPAR and Serra Hunter Program.