Two types of progenitors of the granulocyte series in the human embryonic liver.

Abstract

Neutrophilic granulocyte series in the human liver obtained from 109 embryos between 28 and 49 days after ovulation and 76 fetuses between 8 and 22 wk of gestation was investigated by light microscopy and EM. Hemopoietic cells, considered progenitors of the granulocyte series, and undifferentiated cells first appeared in the intercellular spaces of mesenchymal cells around the ductus venosus of an embryo of 14 mm crown-rump length (estimated age: 40 days after ovulation). The early hepatic myeloid progenitor cells which appeared by 50 days of gestation (early stage of hepatic granulopoiesis) differed in ultrastructure from the late hepatic myeloid progenitor cells which first occurred after 50 days of gestation (late stage of hepatic granulopoiesis). Morphologically, two kinds of hemopoietic stem cells exist in the human embryonic and fetal liver. The hepatic granulocyte series in the early stage differs in it process of maturation from that in the late stage. Endogenous peroxidase activity was demonstrated in small granules of the late hepatic myeloid progenitor cells which appeared lymphoid in ultrastructure.