THE EXPRESSION OF IGG FC-RECEPTORS ON CIRCULATING LEUKOCYTES IN THE FETUS AND NEWBORN

The expression of Fc-gamma-R (FcR) classes on circulating leucocyte lineages (lymphocytes, monocytes, granulocytes) was determined by flow cytometry in 46 fetuses at 18-35 weeks of gestation and in 11 full-term neonates, and compared to that in 20 adults. Classes of FcR present on adult leucocytes could be detected on the corresponding fetal cells as early as 18 weeks of pregnancy. Generally, in the fetus, FcR expression was lower than in the adult while in the neonate it approached values found later in life. However, percentages of Fc-gamma-RIII-positive fetal/new-born monocytes, and those of FcR-positive new-born granulocytes were considerably raised above adult levels. The modified pattern of FcR expression on fetal/new-born leucocytes is likely to influence their IgG-mediated effector activities towards targets such as red cells and platelets.