Considerable effort has been expended to identify genes that account for myeloid 
lineage commitment and development. However, currently available non-invasive 
mouse models utilize myeloid-specific reporters that are significantly expressed 
in hematopoietic stem cells as well as lymphoid compartments. Here, we describe 
a myeloid-specific marker that is not shared by any other lineage. We show that 
lactotransferrin mRNA is expressed by Gr-1(+)/CD11b(+) cells in the bone marrow, 
as opposed to hematopoietic stem cells or any peripheral cell population. To 
follow the progeny of lactotransferrin-expressing bone marrow cells, we 
generated a mouse model in which a reporter gene is irreversibly activated from 
the lactotransferrin-promoter. We found that lactotransferrin-reporter labels a 
majority of neutrophils, monocytes, macrophages and distinct subtypes of 
dendritic cells, while excluding T, B, natural killer cells, 
interferon-producing killer dendritic cells, plasmacytoid dendritic cells, 
erythrocytes and eosinophils. Lactotransferrin-reporter(-) bone marrow cells 
retain lymphoid, erythroid and long-term repopulating potential, while 
lactotransferrin-reporter(+) bone marrow cells confer only myeloid, but not 
lymphoid potential. We conclude that lactotransferrin represents a late stage 
differentiation marker of neutrophils, macrophages and distinct subtypes of 
dendritic cells.