The interleukin-2 receptor on cord blood and nulliparous mononuclear cells is downregulated by maternal and cord blood serum.

The concentration of interleukin-2 receptor (IL-2R) on maternal, cord blood and unrelated nulliparous mononuclear cells has been studied after a previous phytohaemagglutinin (PHA) stimulation. Furthermore, the inhibitive action of maternal and cord blood serum on the IL-2R expression of stimulated nulliparous and cord blood lymphocytes has been shown. A downregulation of the [3H]-thymidine uptake by these PHA treated cells previously incubated in maternal and cord blood serum has been observed. Retroplacental serum was the most inhibitive experimental medium. The IL-2R modulation property of maternal serum has been studied during the pregnancy. Appearing quite early (in the sixth week), the maternal serum dependent inhibitive factor vanished, 2 to 3 weeks after delivery. After a study of the different serum components, it is suggested that the IL-2R downregulating molecule is included in the maternal immunoglobulin (IgG) fraction. Further experiments suggest that the addition of recombinant IL-2 during the action of low doses of maternal IgG allows a partial re-expression of the IL-2R. However, at physiological concentrations of IgG, the IL-2R downregulation becomes irreversible.