Immunocytochemical observations on macrophage populations in normal fetal and adult human liver

Phenotypic expression of macrophages was studied immunocytochemically in 25 human fetal livers at various stages of development and in 20 normal human adult livers. A panel of commercially available polyclonal and monoclonal antibodies (KP1, Mac387, LN3, CR3/43, and antibodies against muramidase, alpha-1-antitrypsin, and factor XIIIa) was applied to paraffin sections. From the seventh week of gestation macrophages in the fetal liver showed differences in distribution with the various antibodies. Macrophages in adult liver similarly varied in morphology and phenotypic expression. In the light of these results, we conclude that the population of human liver macrophages is heterogeneous from an early stage of fetal development and that this heterogeneity extends into adult life.