MPs population was characterized in sputum supernatant, according to the expression of membrane-specific antigens. Anti-human CD11a labelling was used to numerate leukocyte MPs, while numeration of granulocyte MPs and monocyte/macrophage MPs was performed using anti-human CD66b and anti-human CD11b, respectively. Human IgM was used as isotypematched negative control for CD66b staining, while IgG was used as isotype-matched negative control for CD11a and CD11b.