Flow-cytometry analysis of heme oxygenase-1 (HO-1) expression in bone marrow (BM) from subjects with sickle cell disease and healthy donors. (A) Comparison of staining with anti-HO-1 antibody and control antibody in subjects with sickle cell disease (n=2) and healthy child BM donors (n=2, one HbAS, one HbAA), plotted against CD16 expression as a marker of neutrophil maturation. The gated population is CD16 intermediate, and is proposed to represent developing neutrophils. (B) Expression of surface markers which define the maturational stage of developing neutrophils in BM. For each subject with sickle cell disease, the expression of surface markers on the HO-1+CD16intermediate population (gated in A) is presented in comparison with the expression of the same markers in total BM (upper panels). The HO-1+ cells express high levels of CD49d, low levels of CD24, intermediate-to-high levels of CD11b, and intermediate levels of CD15, suggesting they are around the point of transition from proliferating to non-proliferating neutrophil progenitors.