Evaluation of the expression of human CAP18 gene during neutrophil maturation in the bone marrow

To understand the gene expression of CAP18 (18-kDa cationic antibacterial p rotein), a member of cathelicidins, we evaluated mRNA and protein expressio n of CAP18 using human bone marrow cells and mature neutrophils, Northern b lot analysis revealed that CAP18 mRNA was expressed more abundantly in bone marrow cells than mature neutrophils, whereas Western blot analysis indica ted that CAP18 protein was more abundant in mature neutrophils than bone ma rrow cells. Consistent with this, in situ hybridization using bone marrow c ells demonstrated that the expression of CAP18 mRNA Tvas neutrophil lineage -specific and was observed primarily in myelocytes (>95%) with limited expr ession in more immature cells (promyelocytes) and mature cells (metamyelocy tes, band cells, and segmented neutrophils), Furthermore, immunohistochemic al study indicated that, coincident with the increase of CAP18 mRNA levels, CAP18-positive cells increased markedly at myelocyte stage, and the increa sed levels remained almost constant (>95%) in metamyelocytes, band cells, a nd segmented neutrophils, although the mRNA levels were remarkably reduced in these cells. Together these observations indicate that CAP18 gene transc ription likely occurs lineage- and stage-specifically at the myelocyte stag e of neutrophil maturation in the bone marrow and results in the synthesis and cytoplasmic accumulation of CAP18, which is present in the subsequent s tages of neutrophil maturation.