Circulating Myeloid-Derived Suppressor Cells Are Increased and Activated in Pulmonary Hypertension

Background: Myeloid-derived suppressor cells (MDSCs) are increased in inflammatory and autoimmune disorders and orchestrate immune cell responses therein. Pulmonary hypertension (PH) is associated with inflammation, autoimmunity, and lung vascular remodeling. Immature myeloid cells are found in the lungs of humans and animals with PH, and we hypothesized that they would be increased in the blood of patients with PH compared with control subjects. Methods: Twenty-six children with PH and 10 undergoing cardiac catheterization for arrhythmia ablation were studied. Five milliliters of fresh blood were analyzed using flow cytometry. Results were confirmed using magnetic bead sorting and immunofluorescence, while quantitative polymerase chain reaction and intracellular urea concentration assays were used as measures of MDSC arginase-1. activation. Results: Flow cytometry demonstrated enrichment of circulating MDSCs among patients with PH (n = 26; mean, 0.271 x 10(6) cells/mL +/- 0.17; 1.86% of CD45(+) population +/- 1.51) compared with control subjects (n = 10; mean, 0.176 x 10(6) cells/mL +/- 0.05; 0.57% of CD45(+) population +/- 0.29; P < .05). Higher numbers of circulating MDSCs correlated to increasing mean pulmonary artery pressure (r = 0.510, P < .05). Among patients with PH, female patients had a twofold increase in MDSCs compared with male patients. Immunofluorescence analysis confirmed the results of flow cytometry. Quantitative reverse transcription polymerase chain reaction assay results for arginase-1 and measurement of intracellular urea concentration revealed increased activity of MDSCs from patients with PH compared with control subjects. Conclusions: Circulating activated MDSCs are significantly increased in children with PH compared with control subjects. Further investigation of these cells is warranted, and we speculate that they might play significant immunomodulatory roles in the disease pathogenesis of PH. CHEST 2012; 141(4):944-952