IL-2 receptor expression and function on human cord blood mononuclear cells following PHA and anti-CD3 antibody stimulation

Interleukin-2 receptors (IL-2R) on mononuclear cells from human umbilical cord blood were investigated after stimulation by phytohemagglutinin (PHA) and anti-CD3 antibody. The proportion of cells expressing the Tac antigen (IL-2Rα, p55) did not differ from that for adult mononuclear cells. However, the levels of high affinity IL-2R (H-IL-2R) and low affinity IL-2R (L-IL-2R) present on the PHA blasts of cord blood cells were shown to be twice and three times, respectively, that of adults by interleukin-2 (IL-2) binding assay. The level of low affinity IL-2R in the cord blood cells was approximately double that of adult cells after activation by anti-CD3 antibody, but no difference was observed in the levels of high affinity IL-2R. Functional investigation of IL-2R revealed that the amount of internalized IL-2 in PHA-stimulated cord blood mononuclear cells was twice that in adult mononuclear cells but there were no differences between them in the time course of internalization and degradation. Although there were significant numbers of H-IL-2R in premature (25 and 28 weeks) infants following PHA stimulation, there were markedly fewer following anti-CD3 stimulation. Prematurity of the T-cell activation system through the CD3 pathway at this stage is therefore indicated.