The role of interleukin 2 in the regulation of proliferation and IgM synthesis of human newborn mononuclear cells.

The effect of interleukin 2 (IL-2) on cord blood mononuclear cells (CBMC) was studied, with special reference to B cell function. The study shows that CBMCs proliferate in response to recombinant interleukin 2 (rIL-2) without in-vitro preactivation. The response was also detected when whole blood cultures were used. CBMCs not preactivated in vitro proliferated in response to rIL-2 even after T cell and monocyte depletion. Thus, rIL-2 affects both non-T cells and T cells of newborns without preactivation in vitro. IL-2 receptors on unstimulated CBMCs appear to be distinct from Tac antigen, as the mean number of Tac antigen-positive cells among CBMCs was only 0.8%. Furthermore, rIL-2 inhibited PWM-induced proliferation and the response was more prominent in newborns than in adults. Thus, rIL-2 seems to cause a higher increase of suppressor cell function in CBMCs than in adult peripheral blood mononuclear cells. Neither rIL-2 nor Staphylococcus aureus Cowan 1 (SAC) stimulated any IgM synthesis, but a dose-dependent IgM synthesis was obtained by combining SAC and rIL-2. Alone, however, rIL-2 appears to be an insufficient factor to induce differentiation of SAC-activated cord blood B cells, as no IgM production in response to rIL-2 occurred in T cell and monocyte-depleted cell populations. The results of this study suggest both increased suppressor cell function and intrinsic B cell deficiency as causes of a weak humoral immune response in newborns.