Ontogeny of phytohemagglutinin and concanavalin A responses in the human fetus: Effect of thymosin

Abstract

Ontogenic development of phytohemagglutinin (PHA) and concanavalin A (Con A) responses of cells from 22 human fetuses at 6–23 weeks of gestation was studied. The results show that PHA responses appear earlier and stronger than Con A responses during the early fetal period. Similar to the findings reported for the mouse, sheep, and guinea pig, the mitogen responsive cells were first found in the thymus and thereafter in the spleen. The effect of thymosin on human fetal cells was variable, since thymocytes and spleen cells of only 2 out of 13 fetuses studied were susceptible to low concentrations (0.001–0.1 μg/ml) of thymosin. Higher concentrations (1.0–200 μg/ml) increased 5[ 125I]iodo-2′-deoxyuridine ( 125IUdR) uptake of PHA- and Con A-stimulated cells in few fetuses. In the fetal liver and bone marrow, thymosin-induced increase of 125IUdR uptake was observed both in unstimulated and mitogen-stimulated cells, however, without any significant effect on stimulation indices.