Hp and lactoferrin are synthesized at the myelocyte stage and stored in the cytosol of cells throughout granulocyte differentiation. BM populations highly enriched in PMs, MYs, bm-PMNs, and pb-PMNs were isolated from healthy donors. (A) Total RNA was purified from BM and PB populations and subjected to microarray analysis to monitor the expression profiles for Hp and Lf (marker for specific granules) transcripts during granulocyte differentiation (mean ± SD; n = 3).31 (B) Immunocytochemical staining of BM and PB populations using rabbit anti-human Hp and Lf antibodies demonstrates the cytoplasmic localization (red) of Hp and Lf from the myelocyte stage throughout granulocyte differentiation. BM populations highly enriched in PMs stained with rabbit anti-human Hp or Lf antibodies and populations stained with irrelevant rabbit IgG antibodies were all negative. Original magnification, × 400.