Acid alpha-naphthyl acetate esterase activity in nucleated red cells of human fetal liver

Acid alpha-naphthyl acetate esterase (ANAE) activity was investigated in nucleated red cells obtained from nine human fetal livers at 9-24 weeks of gestation. A strong ANAE activity was demonstrated in fetal liver erythroblasts with a staining pattern of a perinuclear ring. Occasionally some polychromatophilic normoblasts expressed a focal ANAE activity usually observed in human T-lymphocytes. Some 50-70% of erythroblasts in human fetal livers showed a ring-like staining pattern. A slight decrease of ANAE positivity was observed in cells of fetal livers after 17 weeks of gestation.