Sputa liquefied with Sputasol, a dithiothreitol formulation, were centrifuged at low speed to remove large debris, and studied by flow cytometry analysis. MPs were readily identified in dot plots ( Figure 1A ) and were positive for CD66b antigen ( Figure 1D ). To discriminate whether bacteria or bacterial bodies could give such image, supernatants were plated onto agar plates and no bacterial growth was observed in sputa obtained from CF patients. However, to evaluate if bacteria could be stained by anti-granulocyte antibodies, Pseudomonas aeruginosa PAO1 were grown for 1 hour and then killed by gentamicin treatment. Although detectable in the same region of MPs ( Figure 1B,) , killed bacteria, analyzed by flow cytometry after antibody binding did not show any positivity for the antibody directed against CD66b ( Figure 1E) .