MP phenotype was analyzed by evaluating the presence of antigens representing different cell types: CD11a for leukocytes, CD66b for granulocytes, CD11b for monocyte/macrophages. In CF patients, amount of MPs expressing CD66b (median value of 53.8%) was higher than those expressing CD11a (median value of 16.1%) and CD11b (median value of 0%). Comparison of all CF patients versus PCD patients showed that amounts of MPs expressing CD66b and CD11a were significantly higher in CF than in PCD (CD66b: p = 0.0068; CD11a: p = 0.0226) (data not shown). No differences in the three populations of MPs were found between patients in acute and stable phase of CF. However, both acute and stable patients showed significantly higher levels of MPs expressing CD66b and CD11a in comparison to PCD patients (for CD66b: stable CF vs. PCD: p = 0.0373; acute CF vs. PCD: p = 0.0046. For CD11a: stable CF vs. PCD: p = 0.0464; acute CF vs. PCD: p = 0.0431; Figure 4 ).